Ch.6 - Thermochemistry WorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Our system is simply our chemical reaction. Anything outside of that is considered our surroundings

Thermodynamics & Thermochemistry

Concept #1: Thermodynamics vs. Thermochemistry

Transcript

Welcome back guys. In this new video we're going to take a look at the energy changes involved in our chemical reactions.
First off, we're going to start off by saying that blank is the branch of physical science concerned with heat and it's transformations to and from other forms of energy. We're going to say that this is called thermodynamics. The part of thermodynamics that we're going to be concerned with is the branch of chemistry that deals with the heat involved in our chemical and physical changes. This branch of chemistry is called thermal chemistry.
Remember when we use the term energy or we use the term heat, they mean the same thing. Heat is just a type of energy. It's thermal energy. Energy of heat. 

Thermodynamics deals with the conversion of energy from one form to another. Thermochemistry is the branch of chemistry dealing with thermal (heat) energy.

Concept #2: System vs. Surroundings

Transcript

When we're talking about thermal energy or heat or energy, we're talking about two basic ideas. We're talking about the specific part of the universe that we're focused on. Since we're in a chemistry course, our system is the part of the universe that we're concerned with. When I say system, I mean our balanced chemical reaction. So any balanced chemical reaction that we're paying attention to when doing word problems, when looking at it on the board when our professor is talking about it, that represents our system, our balanced chemical reaction.
We're going to say everything having to do with that balanced chemical reaction represents our system. Everything outside of it. Everything outside of that, you, me, your professor, the board on which they're talking about, all of that stuff are our surroundings. We have our system and we have our surroundings.
They're not isolated from another. Whatever happens to one, the opposite happens to the other. If our system is gaining energy, the only reason it's gaining energy is because the surroundings are giving that energy to the system, so as a result the surroundings would be losing energy. It also works the opposite way too. Our main concerns are which way is energy traveling. Is it going from our surroundings to our system or our system to our surroundings? 

Endothermic & Exothermic Reactions

Example #1: Whether our system (the chemical reaction)   releases   or   absorbs   heat or energy will determine if it is   exothermic   or   endothermic

Example #2: Classify each of the following process as either exothermic or endothermic:

a)  Fusion of Ice.

b)  Sublimation of CO2.

c)  Vaporization of aqueous water.

d)  Deposition of chlorine gas.

e)  Condensation of water vapor.

Internal Energy of the System

Concept #3: Understanding the internal energy of the system

Transcript

Welcome back guys. In this new video, we're going to look at the energy flow to or from a system.
We say that the first law of thermodynamics states that energy can't be created nor destroyed. All that happens is it changes forms. What this really means is anytime we have a balanced chemical reaction, remember we say that the number of atoms and the types of atoms have to be the same on both sides. If I start out with ten hydrogens as reactants, I have to end with ten hydrogens as products. That's what the first law of thermodynamics really is saying.
We're going to say we've discussed systems versus surroundings. These are the two types of concepts we're dealing with when it comes to energy changes. We're going to say that the system either gains or loses energy based on the surroundings. But now we're going to pay more attention to the surroundings.
We're going to say we're normally concerned with just the surroundings and we're going to use this equation here, delta E equals q plus w. We're going to say that delta E represents the internal energy of our system. We're going to say when it comes to the variable q, q also equals delta H. Delta H is enthalpy. When we talk about enthalpy, enthalpy just means that a reaction either absorbs or release heat or energy in order for the reaction to occur. That's all enthalpy is concerned with. We're also going to say that w equals negative pressure times the change in volume. Pressure here will be in atmospheres. This delta V means change in volume. That means final volume minus initial volume. The volume here is usually in liters. 

The internal energy (ΔE or ΔU)  of the system can be calculated from the heat and work of the system.

Concept #4: Heat vs. Work

Transcript

When we say q, q means heat and w equals work. When it comes to these two terms, they can either be positive or negative based on certain keywords that your professors like to us. We're going to say that q, it can be positive when we say that the system gains, takes in, or absorbs heat or energy from the surroundings. We say that q can be negative when we say the system loses, evolves, gives off or releases heat or energy to the surroundings.
If the system is absorbing energy, why is it doing that? It's because the surroundings are giving it to it. If the system is losing energy, where is it going? It's going to our surroundings.
For work, we're going to say that work can also be positive or negative. We're going to say when work is done on the system by the surroundings, then work will be positive. They keyword we're going to see here is volume compresses. Basically, volume gets smaller. If the volume is getting smaller, that means that the surroundings are doing work on our system.
Work could be negative if we say that when work done by system on the surroundings. Keyword here, volume expands. The volume increases. If you see the volume increasing, that's because our system is doing that. It's doing the work. Therefore, work would be negative.
What you need to remember is what's the equation for the internal energy of the system and will my work and heat be positive or negative based on certain keywords that the professor will ask. 

The signs of heat (q) and work (w) of the system can be either negative or positive depending on the key words stated. 

Example #3: Which of the following signs on q and w represent a system that is doing work on the surroundings, as well as losing heat to the surroundings?

q = - , w = -                   q = +, w = +          

q = -, w = +                   q = +, w =  -

 

Internal Energy Calculations

Work is one key variable to find the internal energy of the system. It’s equals to – PΔV.

Concept #5: Calculating work

Transcript

Welcome back guys. In this new video, we're going to work out calculations on the amount of energy that flows to and from systems.
In this first question, it says an unknown gas expands in a container, increasing the volume from 4.3 liters to 8.2 liters at a constant pressure of 931 millimeters of mercury. For part A, it says calculate the work done in kilojoules by the gas as it expands.
Because of the way that the formula for work is set up, we'll have an answer in liters times atmospheres. What we should realize is there's a conversion factor to go from liters times atmospheres to joules. This is the conversion factor you need to know. We're going to say one liter times atmospheres equals 101.3 joules.
We're looking for work and we said that the formula for work is work equals negative pressure in atmospheres times the change in volume, which is just final volume minus initial volume. The units for volume will be in liters.
I give you 931 millimeters of mercury, so the first thing we need to do is convert that to atmospheres. We have 931 millimeters of mercury. Hopefully, you guys remember that for every one atmosphere, we have 760 milliliters of mercury. This and this cancel out. Just remember that conversion. We're going to say one atmosphere equals 760 milliliters of mercury and also one atmosphere equals 760 torrs. These are all just units of pressure. These are the conversion factors you need to remember.
When we do that we get 1.225 atmospheres. There goes my pressure and atmosphere, so I can plug that into my formula. So negative 1.225 atmospheres times the change in volume, which is final volume minus initial volume, so 8.2 liters, which is our final, minus 4.3 liters.
Now what we do there is it's going give me to negative 4.7775 liters times atmospheres. Those are our units. Remember I want the answer in kilojoules, so first we have to convert liters times atmospheres to joules. We want to get rid of liters times atmospheres, so we put that on the bottom. Remember for every one liter times atmospheres we have 101.3 joules.
We want to change joules to kilojoules. Remember we want to get rid of joules, so it goes on the bottom, kilojoules go on the top. Kilo- is a metric prefix. We said that one is associated with the metric prefix. One kilo is 10 to the 3 joules.
Multiply everything on the top. Divide by everything on the bottom. Remember 10 to the 3 is also equivalent to 1000. You could also plug that in. When we do that we get negative 0.483961 kilojoules. Here we'll just round it to three sig fig's. Here I'm not asking you for the number of sig figs directly, so we can just keep it at three sig figs. So it will be negative 0.484 kilojoules. That's the amount of work that the system is doing on the surroundings.
Remember we know that the system is doing work because we say that any time we use the word expand, the volume is increasing. And what's causing that increase? Our system. 

Once we’ve calculated work we can calculate the internal energy of the system once we also calculate the heat released or absorbed. 

Concept #6: Calculating heat and the   internal energy of the system

Transcript

Using part A calculate the internal energy of the system if the system absorbs 2.3 kilojoules of energy. Remember internal energy of the system is delta E. Delta E equals q plus w. Here we're going to say the system is absorbing. That's one of the keywords we used. It's absorbing that much energy. When we say absorbs that means q, which is energy, which is heat, is positive. We have a positive 2.3 kilojoules plus a negative 0.483961 kilojoules. Work that out and it gives us 1.82 kilojoules at the end. That would be the internal energy of our system. The energy of our system increases by that much. 

Under certain conditions either q (heat) or w (work) can be equal to zero. This makes it easier to calculate the internal energy of the system. 

Concept #7: Calculating the internal energy of the system in a vacuum

Transcript

So guys, for Part C it says, using part being calculate the internal energy of the system and the system does work against a vacuum. So, remember internal energy is Delta e equals q, which is heat, plus W, which is work. Now, remember from the Part B they told that, they told us that our system absorbs 2.3 kilojoules of energy. So, that means that our energy here is positive because we're taking it in, we're absorbing but now they're telling us we're doing work against a vacuum. Remember, work equals negative pressure times the change in volume, just realize this, when we're talking about a vacuum where do you imagine vacuums exist? vacuums exist in space and in space you can just think of there being 0 pressure. So, as a result here, our pressure is 0, anything times 0 is equal to 0. So, work done against the vacuum means that no work is being done. So, W here equals 0, therefore the internal energy of our system has to be 2.3 kilojoules, all the energy is coming from the heat that's absorbed from Part B. Now, that we've seen this continue on to the practice question and you the information you learn so far about heat and work to help you figure out the internal energy of your system.

When work is done against a vacuum the pressure is equal to 0 atm. Since ΔE = q + w, the equation becomes only ΔE = q

Practice: The reaction of nitrogen with hydrogen to make ammonia has an enthalpy, ?H = - 92.2 kJ: N2 (g) + 3 H2 (g) ----> 2 NH3 (g) What is in the internal energy of the system if the reaction is done at a constant pressure of 20.0 atm and the volume compresses from 10 L to 5 L?

Additional Problems
Which statement is not correct? a. Internal energy, E, is a state function. b. Heat and work are state functions. c. Heat is given off to the surroundings in an exothermic reaction. d. The enthalpy change is the heat of reaction at constant pressure. e. Enthalpy is a state function.
1 L.atm =101.325 J When 2.00 kJ of energy is transferred as heat to nitrogen in a cylinder fitted with a piston at an external pressure of 2.00 atm, the nitrogen gas expands from 2.00 to 5.00 L against this constant pressure. What is ∆U for the process? 1. 0 2. −0.608 kJ 3. +1.39 kJ  4. +2.61 kJ 5. −2.61 kJ
DO NOT FORGET TO WRITE A BALANCED CHEMICAL EQUATION!! The combustion of one mole of octane (C8H18(l)) to produce carbon dioxide and liquid water has ∆Hr = −5471 kJ · mol−1 at 298K. What is the change in internal energy for this reaction? 1. −5460 kJ · mol−1 2. −5493 kJ · mol−1 3. −5471 kJ · mol−1 4. −5449 kJ · mol−1 5. −5482 kJ · mol−1
A system releases 415 kJ of heat and does 125 kJ of work on the surroundings. What is the change in internal energy of the system? 
The gas in a piston is warmed and absorbs 655 J of heat. The expansion of the piston performs 344 J of work on the surroundings. Find the change in internal energy of the system. 
The change in enthalpy (∆H) is a measure of the heat of reaction at 1) Constant temperature. 2) Constant pressure. 3) Constant volume. 4) Constant internal energy. 5) Constant entropy. 
What is internal energy?
Is internal energy a state function?
In which direction does energy flow?
What is heat?
Explain the difference between heat and temperature.
How is the change in internal energy of a system related to heat and work?
Explain how the sum of heat and work can be a state function, even though heat and work are themselves not state functions.
What is pressure-volume work?
Identify each of the following energy exchanges as primarily heat or work and determine whether the sign of E is positive or negative for the system. a. Sweat evaporates from skin, cooling the skin. (The evaporating sweat is the system.) b. A balloon expands against an external pressure. (The contents of the balloon is the system.) c. An aqueous chemical reaction mixture is warmed with an external flame. (The reaction mixture is the system.)Identify energy exchanges as primarily heat or work.
Explain the significance of the law of conservation of energy.
Which of the following cannot leave or enter a closed system: heat, work, or matter?
What do we call the part of the universe that is not part of the system?
Which cannot leave or enter an isolated system?
The accompanying photo shows a pipevine swallowtail caterpillar climbing up a twig. Does the caterpillar do work in climbing the twig? Explain.
The accompanying photo shows a pipevine swallowtail caterpillar climbing up a twig. Does the amount of work done in climbing a 12-inch section of the twig depend on the speed of the caterpillars climb?
Imagine a container placed in a tub of water, as depicted in the accompanying diagram. If neither the volume nor the pressure of the system changes during the process, how is the change in internal energy related to the change in enthalpy?
The accompanying photo shows a pipevine swallowtail caterpillar climbing up a twig. Does the change in potential energy depend on the caterpillars speed of climb?
You lose 9 pounds over a 26-day period. Which of the following quantities act like a state function: the amount of calories you consume, your weight, or the number of calories burned through exercise?
What is meant by the internal energy of a system?
By what means can the internal energy of a closed system increase?
Imagine that you are climbing a mountain.Is the distance you travel to the top a state function?
Imagine that you are climbing a mountain.Is the change in elevation between your base camp and the peak a state function?
Consider the two diagrams below. The equations you obtained in parts (a) and (b) are based on what law?
Consider the two diagrams below. Would similar relationships hold for the work involved in each process? Why?
At 20 oC (approximately room temperature) the average velocity of N2 molecules in air is 1050 mph.What is the kinetic energy (in J) of an N2 molecule moving at this speed?
At 20 oC (approximately room temperature) the average velocity of N2 molecules in air is 1050 mph.What is the total kinetic energy of 1 mol of N2 molecules moving at this speed?
Suppose an Olympic diver who weighs 54.0 kg executes a straight dive from a 10-m platform. At the apex of the dive, the diver is 10.8 m above the surface of the water. You may want to reference (Pages 165 - 166)Section 5.1 while completing this problem.What is the potential energy of the diver at the apex of the dive, relative to the surface of the water?
A sample of gas is contained in a cylinder-and-piston arrangement. It undergoes the change in state shown in the drawing. Assume first that the cylinder and piston are perfect thermal insulators that do not allow heat to be transferred. What can be said about E for the state change?
A sample of gas is contained in a cylinder-and-piston arrangement. It undergoes the change in state shown in the drawing. Assume first that the cylinder and piston are perfect thermal insulators that do not allow heat to be transferred. Now assume that the cylinder and piston are made up of a thermal conductor such as a metal. During the state change, the cylinder gets warmer to the touch. What is the sign of q for the state change in this case? Describe the difference in the state of the system at the end of the process in the two cases. What can you say about the relative values of E?
Consider the systems shown in the following figure. In one case the battery becomes completely discharged by running the current through a heater, and in the other by running a fan. Both processes occur at constant pressure. In both cases the change in state of the system is the same: The battery goes from being fully charged to being fully discharged. Yet in one case the heat evolved is large, and in the other it is small. Is the enthalpy change the same in the two cases?
A system goes from state 1 to state 2 and back to state 1.Without further information, can you conclude that the amount of heat transferred to the system as it goes from state 1 to state 2 is the same or different as compared to that upon going from state 2 back to state 1?
Identify the force present, and explain whether work is being performed in the following cases.You lift a pencil off the top of a desk.
A standard air conditioner involves a refrigerant that is typically now a fluorinated hydrocarbon, such as CH2F2. An air-conditioner refrigerant has the property that it readily vaporizes at atmospheric pressure and is easily compressed to its liquid phase under increased pressure. The operation of an air conditioner can be thought of as a closed system made up of the refrigerant going through the two stages shown here (the air circulation is not shown in this diagram). During expansion, the liquid refrigerant is released into an expansion chamber at low pressure, where it vaporizes. The vapor then undergoes compression at high pressure back to its liquid phase in a compression chamber. What is the sign of q for the expansion?
Identify the force present, and explain whether work is being performed in the following cases.A spring is compressed to half its normal length.
A standard air conditioner involves a refrigerant that is typically now a fluorinated hydrocarbon, such as CH2F2. An air-conditioner refrigerant has the property that it readily vaporizes at atmospheric pressure and is easily compressed to its liquid phase under increased pressure. The operation of an air conditioner can be thought of as a closed system made up of the refrigerant going through the two stages shown here (the air circulation is not shown in this diagram). During expansion, the liquid refrigerant is released into an expansion chamber at low pressure, where it vaporizes. The vapor then undergoes compression at high pressure back to its liquid phase in a compression chamber. What is the sign of q for the compression?
Identify the force present, and explain whether work is done in the following cases.A positively charged particle moves in a circle at a fixed distance from a negatively charged particle.
Identify the force present, and explain whether work is done in the following cases.An iron nail is pulled off a magnet.
Is a human being an isolated, closed, or open system?
Electrostatic potential energy. At finite separation distances for two charged particles, Eel is positive for like charges and negative for opposite charges. As the particles move farther apart, their electrostatic potential energy approaches zero.A positively charged particle and a negatively charged particle are initially far apart. What happens to their electrostatic potential energy as they are brought closer together?
Write an equation that expresses the first law of thermodynamics in terms of heat and work.
The internal energy of an ideal gas depends only on its temperature.Explain.
What is meant by the term state function?
Give an example of a quantity that is a state function and one that is not.
Is the volume of the system a state function?
H is a state function, but q is not a state function. Explain.
A system that does work on its surroundings.If the amount of zinc used in the reaction is increased, will more work be done by the system? Is there additional information you need in order to answer this question?
You may want to reference (Pages 177 - 178) Section 5.4 while completing this problem.Under what condition will the enthalpy change of a process equal the amount of heat transferred into or out of the system?
You may want to reference (Pages 177 - 178) Section 5.4 while completing this problem.During a constant-pressure process, the system releases heat to the surroundings. Does the enthalpy of the system increase or decrease during the process?
What is work?
What is a state function?
List some examples of state functions.
Sign conventions for heat and work. Heat, q, gained by a system and work, w, done on a system are both positive quantities, corresponding to "deposits" of internal energy into the system. Conversely, heat transferred from the system to the surroundings and work done by the system on the surroundings are both "withdrawals" of internal energy from the system.Suppose a system receives a “deposit” of 51 J of work from the surroundings and loses a “withdrawal” of 83 J of heat to the surroundings. What is the magnitude and the sign of E for this process?
A gas is confined to a cylinder under constant atmospheric pressure, as illustrated in the following figure. When the gas undergoes a particular chemical reaction, it absorbs 826 J of heat from its surroundings and has 0.66 kJ of P-V work done on it by its surroundings. What is the value of E for this process?
During a normal breath, our lungs expand about 0.50 L against an external pressure of 1.0 atm. How much work is involved in this process (in J)?
A sample of gas is contained in a cylinder-and-piston arrangement. It undergoes the change in state shown in the drawing. Assume first that the cylinder and piston are perfect thermal insulators that do not allow heat to be transferred. What is the value of q for the state change?
Consider the accompanying energy diagram. (a) Does this diagram represent an increase or decrease in the internal energy of the system?
The contents of the closed box in each of the following illustrations represent a system, and the arrows show the changes to the system during some process. The lengths of the arrows represent the relative magnitudes of q and w. (a) Which of these processes is endothermic?
Which statement is true of the internal energy of a system and its surroundings during an energy exchange with a positive E system?The internal energy of the system and the surroundings is 0The internal energy of the system and surroundings increasesThe internal energy of the system decreases and the internal energy of the surroundings increasesThe internal energy of the system and surroundings decreaseThe internal energy of the system increases and the internal energy of the surroundings decreases 
In the accompanying cylinder diagram a chemical process occurs at constant temperature and pressure. (a) Is the sign of w indicated by this change positive or negative?
Imagine a container placed in a tub of water, as depicted in the accompanying diagram. (a) If the contents of the container are the system and heat is able to flow through the container walls, what qualitative changes will occur in the temperatures of the system and in its surroundings? What is the sign of q associated with each change? From the system’s perspective, is the process exothermic or endothermic?
At constant pressure, which of these systems do work on the surroundings?a. 2A(g) + 3B(g) → 4C(g)b. A(s) + B(g) → 2C(g)c. A(g) + B(g) → 3C(g)d. A(s) + 2B(g) → C(g)e. More than one of the above 
Which statement is true of the internal energy of a system and its sorroundings during an energy exchange with a positive ΔEsys?A. The internal energy of the system decreases and the internal of the surroundings increases.B. The internal energy of the system increases and the internal energy of the surroundings decreases.C. The internal energy of both the system and the surroundings decreases.D. The internal energy of both system and the surroundings increases.
Which one of the following statements is FALSE?The first law of thermodynamics says that the energy lost by the system must be gained by the surroundings.A positive ΔH corresponds to an endothermic process.The enthalpy change for a reaction is independent of the state of the reactants and products.The change of internal energy is the sum of heat and workIf work is done by the system, the sign of work is negative
A rolling billiard ball collides with another billiard ball. That billiard ball (defined as the system) stops rolling after the collision. Identify the energy exchange and the sign of ΔE for the system.A. work; - ΔEB. work; + ΔEC. heat; - ΔED. heat; + ΔE
Suppose an Olympic diver who weighs 52.0 kg executes a straight dive from a 10-m platform. At the apex of the dive, the diver is 10.8 m above the surface of the water. (c) Does the diver do work on entering the water? Explain.
All of the following statements are true EXCEPT:a. energy is a state property.b. the magnitude of delta H is proportional to the limiting reagent.c. the magnitude of delta H for a reaction is equivalent to that of the reverse reaction.d. the magnitude of delta H is proportional to the amount of product produced.e. the magnitude of delta H is dependent upon the intermediate steps in the chemical reaction.
(b) An adult person radiates heat to the surroundings at about the same rate as a 100-watt electric incandescent lightbulb. What is the total amount of energy in kcal radiated to the surroundings by an adult in 24 h?
Limestone stalactites and stalagmites are formed in caves by the following reaction:Ca2+ (aq) + 2 HCO3– (aq) → CaCO3 (s) + CO2 (g) + H2O (l)If 1 mol of CaCO3 forms at 298 K under 1 atm pressure, the reaction performs 2.47 kJ of P-V work, pushing back the atmosphere as the gaseous CO2 forms. At the same time, 38.95 kJ of heat is absorbed from the environment. What are the values of ΔH and of ΔE for this reaction? 
A gas is allowed to expand at constant temperature from a volume of 2.0 L to 11.2 L against an external pressure of 0.750 atm. If the gas absorbs 128 J of heat from the surroundings, what are the values of q, w, and ΔE respectively? a. 128 J, 6.9 J, 135 J b. 128 J, -6.9 J, 121 J c. 128 J, 697 J, 825 J d. 128 J, -697 J, -569 J e. -128 J, -6.9 J, -135 J
For the following processes, calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic: (a) A balloon is heated by adding 850 J of heat. It expands, doing 382 J of work on the atmosphere.
For the following processes, calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic: (b) A 50-g sample of water is cooled from 30°C to 15°C, thereby losing approximately 3140 J of heat. 
For the following processes, calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic: (c) A chemical reaction releases 6.47 kJ of heat and does no work on the surroundings.
A balloon is inflated from 0.0100 L to 0.400 L against an external pressure of 10.00 atm. How much work is done in joules? (101.3 J = 1 L. atm)a. -395 Jb. -0.395 Jc. -39.5 Jd. 39.5 Je. 0.395 J
Which set of signs for q and w represent a system that is doing work on the surroundings and losing heat to the surroundings?a) -q, -wb) +q, +wc) -q, +wd) +q, -we) None of these represent the system referenced above. 
A typical breath is around 0.5 L, but to get 2 sig figs, let’s assume you breathe in 0.48 L. How much work is done when you exhale against an atmosphere pressure of 750 mmHg? Be sure to include a + or - sign in your answer.
A system that does no work but which receives heat from the surroundings has: a) q < 0, ΔE > 0 b) q > 0, ΔE < 0 c) q = ΔE d) q = -ΔE e) w = ΔE
Consider an ideal gas enclosed in a 1.00 L container at an internal pressure of 10.0 atm.Calculate the work, w, if the gas expands against a constant external pressure of 1.00 atm to a final volume of 25.0 L. Now calculate the work done if this process is carried out in two steps.1. First, let the gas expand against a constant external pressure of 5.00 atm to a volume of 5.00 L.2. From there, let the gas expand to 25.0 L against a constant external pressure of 1.00 atm.
Consider an ideal gas enclosed in a 1.00 L container at an internal pressure of 10.0 atm. Calculate the work, w, if the gas expands against a constant external pressure of 1.00 atm to a final volume of 10.0 L.
The heat of vaporization of water at 373 K is 40.7 kJ/mol. Find q, w, ΔE, and ΔH for the evaporation of 454 g of water at this temperature.   
Which expression describes the heat evolved in a chemical reaction when the reaction is carried out at constant pressure? Explain.a. ∆E – wb. ∆Ec. ∆E – q
When 1 mol of a gas burns at constant pressure, it produces 2418 J of heat and does 51 of work. Identify ∆E, ∆H, q, and w for the process. 
Which statement is true of a reaction in which ∆V is positive? Explain. a. ∆H = ∆Eb. ∆H > ∆Ec. ∆H < ∆E
Which is true when a gas expands isothermically against a constant pressure of two atmosphere (mark all that apply)?a. The system does not work.b. The gas releases heat.c. Heat is absorbed by the gas.d. The temperature of the gas decreases.e. No heat flows.
What is the change in the internal energy (in J) of a system that releases 1000 J of heat and does 225 J of work on the surroundings?a. -10,155b. -1225c. -775d. 775e. 1225
If the volume of a system increases from 10.0 L to 14.5 L against a constant external pressure of 1.00 atm, and absorbs 655 J of heat, what is the change in internal energy of the system (∆Esys)? (1 L∙atm = 101.3 J)A) 199 JB) 1111 JC) 651 JD) −1111 JE) −199 J
A certain liquid has Δvap Ho = 26.0 kJmol -1. Calculate q, w, ΔU, and ΔH when 0.50 mol is vaporized at 250K and 750 Torr.
Which one of the following thermodynamic quantities is not a state function?a) workb) enthalpyc) entropyd) internal energye) free energy 
A gas at 25.00°C and 360.00 torr (760 torr = 1atm) expands from 25.0 L to 35.0 L. What is the value of the work done on or by the gas? (1 L•atm = 101.325 J) a. 480 Jb. 3600 Jc. -3600 Jd. 1013.25 Je. -480 J
Which set of signs for q and w represent a system that is doing work on the surroundings and losing heat to surroundings?a. – q, -wb. + q, +wc. – q, +wd. + q, -we. None of these represent the system referenced above.
When fuel is burned in a cylinder equipped with a piston, the volume expands from 0.255 L to 1.45 L against an external pressure of 1.02 atm. In addition, 875 J is emitted as heat. What is the ∆E? (101.3 J = 1 L • atm) 
Heat absorbed by a system at constant volume is equal to1. ∆G2. ∆S3. ∆H4. ∆V5. ∆E 
Which of the following statements concerning the first law of thermodynamics is/are true?I) The internal energy of the universe is always increasing.II) Internal energy lost by a system is always gained by surroundings.III) The universe is an isolated system.1. II and III only2. III only3. I and II only4. II only5. I and III only6. I, II and III7. I only
Heat is1) A measure of temperature.2) A measure of the change in temperature.3) A measure of thermal energy.4) A measure of thermal energy transferred between two bodies at different temperatures.5) All of the above.
A gas is allowed to expand, at a constant temperature, from a volume of 1.0 L to 10.1 L against an external pressure of 0.50 atm. If the gas absorbs 250 J of heat from the surroundings, what are the values of q, w, and ∆E?
Which of the following depicts a situation where the least amount of work is done by a sample of gas? [1 atm = 101325 Pa]a) A 20-L sample of gas expands to 500 L against a vacuumb) A 1-L sample of gas expands to 30 L against a pressure of 2.22 atmc) A 1-L sample of gas expands to 30 L against a pressure of 2.22 Pad) A 20-L sample of gas expands to 500 L against a pressure of 30 atme) Two or more are tied
Calculate the amount of work done when 2.5 mole of H 2O vaporizes at 1.0 atm and 25°C. Assume the volume of liquid H2O is negligible compared to that of vapor. (1 L atm = 101.3 J)1) -61.9 J2) -6.19 kJ3) 61.9 J4) 5.66 kJ5) 518 J
Which statement is always true of the internal energy of a system and its surroundings during an energy exchange with an endothermic value of ΔUsystem?a) ΔHsurroundings > 0b) The internal energy of the system and surroundings increase togetherc) The internal energy of the system decreases while the internal energy of the surroundings increasesd) The internal energy of the system and surroundings decrease togethere) The internal energy of the system increases while the internal energy of the surroundings decreases
The internal energy of a system is the sum of all of its ___.A. thermal energy and kinetic energyB. potential energy and chemical energyC. thermal energy and chemical energyD. potential energy and kinetic energy
Calculate the work for the expansion of CO2  from 1.0 to 3.0 liters against a pressure of 1.0 atm at constant temperature.
Oxygen gas at 34.5°C is compressed from 45.7 L to 34.5 L against a constant pressure of 0.987 atm. If the oxygen gas is defined as the system, how much work is done (in J) on the system? (1 L atm = 101.3 J)A. 1.12 × 103 JB. −1.11 × 101 JC. 1.11 × 101 JD. −4.55 × 103 JE. −1.12 × 103 J
Which of the following is not a state function?A. PressureB. ConcentrationC. Internal energyD. Work
If the internal energy of the products of a reaction is higher than the internal energy of the reactants, what is the sign of ΔE for the reaction?
In which of these cases do the surroundings do work on the system?a. q = -47 kJ, w = +88 kJb. q = +82 kJ, w = -47 kJc. q = +47 kJ, w = 0
Which of the following is true of the internal energy of a system and its surroundings during an energy exchange with a negative ΔEsys?a. The internal energy of the system increases and the internal energy of the surroundings decreases.b. The internal energy of both the system and the surroundings increases.c. The internal energy of both the system and the surroundings decreases.d. The internal energy of the system decreases and the internal energy of the surroundings increases.
During an energy exchange, a chemical system absorbs energy from its surroundings. What is the sign of ΔEsys for this process?
Identify each of the following energy exchanges as primarily heat or work and determine whether the sign of E is positive or negative for the system.a. Sweat evaporates from skin, cooling the skin. (The evaporating sweat is the system.)b. A balloon expands against an external pressure. (The contents of the balloon is the system.)c. An aqueous chemical reaction mixture is warmed with an external flame. (The reaction mixture is the system.)Determine whether the sign of E is positive or negative for the system.
A gas is confined to a cylinder fitted with a piston and an electrical heater, as shown here:Suppose that current is supplied to the heater so that 100 J of energy is added. Consider two different situations. In case (1) the piston is allowed to move as the energy is added. In case (2) the piston is fixed so that it cannot move.In which case does the gas have the higher temperature after addition of the electrical energy?  
A gas is confined to a cylinder fitted with a piston and an electrical heater, as shown here:Suppose that current is supplied to the heater so that 100 J of energy is added. Consider two different situations. In case (1) the piston is allowed to move as the energy is added. In case (2) the piston is fixed so that it cannot move.Identify the sign (positive, negative, or zero) of q and w in case (1).        
A gas is confined to a cylinder fitted with a piston and an electrical heater, as shown here:Suppose that current is supplied to the heater so that 100 J of energy is added. Consider two different situations. In case (1) the piston is allowed to move as the energy is added. In case (2) the piston is fixed so that it cannot move.In which case is E for the system (the gas in the cylinder) larger?
A gas is confined to a cylinder fitted with a piston and an electrical heater, as shown here:Suppose that current is supplied to the heater so that 100 J of energy is added. Consider two different situations. In case (1) the piston is allowed to move as the energy is added. In case (2) the piston is fixed so that it cannot move.Identify the sign (positive, negative, or zero) of q and w in case (2).
The accompanying photo shows a pipevine swallowtail caterpillar climbing up a twig. As the caterpillar climbs, its potential energy is increasing. What source of energy has been used to effect this change in potential energy?
Consider the conversion of compound A into compound B : A  →  B. For both compounds A and B, ΔH˚f > 0. Sketch an enthalpy diagram for the reaction.
Assume that the following reaction occurs at constant pressure:2 Al(s) + 3 Cl2(g) → 2 AlCl3(s)(a) If you are given ΔH for the reaction, what additional information do you need to determine ΔE for the process?(b) Which quantity is larger for this reaction? (c) Explain your answer to part (b).
Consider a system consisting of the following apparatus, in which gas is confined in one flask and there is a vacuum in the other flask. The flasks are separated by a valve. Assume that the flasks are perfectly insulated and will not allow the flow of heat into or out of the flasks to the surroundings. When the valve is opened, gas flows from the filled flask to the evacuated one.Is work performed during the expansion of the gas? Why or why not?
In the cylinder diagrammed below , a chemical process occurs at constant temperature and pressure.Is the sign of w indicated by this change positive or negative?        
In the cylinder diagrammed below , a chemical process occurs at constant temperature and pressure.Given that the process is endothermic, does the internal energy of the system within the cylinder increase or decrease during the change, and is E positive or negative?    
A balloonist begins a trip in a helium-filled balloon in early morning when the temperature is 15°C. By mid-afternoon, the temperature is 30.°C. Assuming the pressure remains at 1.00 atm, for each mole of helium, explain the relationship between the heat (q) transferred (in J) and ΔH for the process (in J).
Suppose an Olympic diver who weighs 54.0 kg executes a straight dive from a 10-m platform. At the apex of the dive, the diver is 10.8 m above the surface of the water.You may want to reference (Pages 165 - 166)Section 5.1 while completing this problem.What is the potential energy of the diver at the apex of the dive, relative to the surface of the water?Assuming that all the potential energy of the diver is converted into kinetic energy at the surface of the water, at what speed in m/s will the diver enter the water?
Suppose an Olympic diver who weighs 54.0 kg executes a straight dive from a 10-m platform. At the apex of the dive, the diver is 10.8 m above the surface of the water.You may want to reference (Pages 165 - 166)Section 5.1 while completing this problem.(a) What is the potential energy of the diver at the apex of the dive, relative to the surface of the water? (b) Assuming that all the potential energy of the diver is converted into kinetic energy at the surface of the water, at what speed, in m/s, will the diver enter the water? (c) Does the diver do work on entering the water? Explain.
The air bags that provide protection in autos in the event of an accident expand because of a rapid chemical reaction. The air bags give off heat when they expand.From the viewpoint of the chemical reactants as the system, what do you expect for the signs of q and w in this process?
An aluminum can of a soft drink is placed in a freezer. Later, you find that the can is split open and its contents frozen. Work was done on the can in splitting it open.Where did the energy for this work come from?        
Energy diagram for the reaction 2 H2(g) + O2(g) → 2 H2O(l) is shown below.The internal energy for Mg(s) and Cl2(g) is greater than that of MgCl2(s). Sketch the energy diagram that represents the reaction MgCl2(s) → Mg(s) + Cl2(g).
Consider the systems shown in the following figure. In one case the battery becomes completely discharged by running the current through a heater, and in the other by running a fan. Both processes occur at constant pressure. In both cases the change in state of the system is the same: The battery goes from being fully charged to being fully discharged. Yet in one case the heat evolved is large, and in the other it is small.What can you say about the relationship between enthalpy change and q in this case, as compared with others that we have considered?
The circles represent a phase change at constant temperature:Is the value of the following positive (+), negative (−), or zero: q  sys?
The circles represent a phase change at constant temperature:Is the value of the following positive (+), negative (−), or zero: ΔE  sys?
The circles represent a phase change at constant temperature:Is the value of the following positive (+), negative (−), or zero: ΔE  univ?
The scene below represents a physical change taking place in a piston-cylinder assembly:Is wsys +, −, or 0?
The scene below represents a physical change taking place in a piston-cylinder assembly:Is ΔHsys +, −, or 0?
The scene below represents a physical change taking place in a piston-cylinder assembly:Can you determine whether ΔEsurr is +, −, or 0? Explain.
In which of the following systems is(are) work done by the surroundings on the system? Assume pressure and temperature are constant.a. 2SO2 (g) + O2 (g) → 2SO3 (g)b. CO2 (s) → CO2 (g)c. 4NH3 (g) + 7O2 (g) → 4NO2 (g) + 6H2O (g)d. N2O4 (g) → 2NO2 (g)e. CaCO3 (s) → CaCO (s) + CO2 (g)
Consider the energy diagram shown in the figure .Does this diagram represent an increase or decrease in the internal energy of the system?        
Consider the energy diagram shown in the figure .What sign is given to E for this process?        
You may want to reference (Pages 167 - 172) Section 5.2 while completing this problem.The contents of the closed box in each of the illustrations represent a system, and the arrows show the changes to the system during some process. The lengths of the arrows represent the relative magnitudes of q and w.For which of these processes, if any, is ΔE > 0?
The contents of the closed box in each of the illustrations  represent a system, and the arrows show the changes to the system during some process. The lengths of the arrows represent the relative magnitudes of q and w.For which process, if any, is there a net gain in internal energy?
Consider a system consisting of two oppositely charged spheres hanging by strings and separated by a distance r1, as shown in the accompanying illustration. Suppose they are separated to a larger distance r2, by moving them apart along a track.What change, if any, has occurred in the potential energy of the system?        
Consider a system consisting of two oppositely charged spheres hanging by strings and separated by a distance r1, as shown in the accompanying illustration. Suppose they are separated to a larger distance r2, by moving them apart along a track.What effect, if any, does this process have on the value of E?        
Which of the following is true of the internal energy of the system and its surroundings following a process in which ΔEsys = +65 kJ.a. The system and the surroundings both lose 65 kJ of energy.b. The system and the surroundings both gain 65 kJ of energy.c. The system loses 65 kJ of energy and the surroundings gain 65 kJ of energy.d. The system gains 65 kJ of energy and the surroundings lose 65 kJ of energy.
Consider a system consisting of two oppositely charged spheres hanging by strings and separated by a distance r1, as shown in the accompanying illustration. Suppose they are separated to a larger distance r2, by moving them apart along a track.What can you say about q and w for this process?
The internal energy of an ideal gas depends only on its temperature. Which of the following is true of an isothermal (constant-temperature) expansion of an ideal gas against a constant external pressure?a. ΔE is positiveb. w is positivec. q is positived. ΔE is negative
You may have noticed that when you compress the air in a bicycle pump, the body of the pump gets warmer.Assuming the pump and the air in it comprise the system, what is the sign of w when you compress the air?
The methane molecule, CH4, has the geometry shown in following figure. Imagine a hypothetical process in which the methane molecule is "expanded," by simultaneously extending all four C–H bonds to infinity. We then have the process CH4(g) → C(g) + 4 H(g). Compare this process with the reverse of the reaction that represents the standard enthalpy of formation.
You may have noticed that when you compress the air in a bicycle pump, the body of the pump gets warmer.What is the sign of q for this process?
You may want to reference (Pages 167 - 172) Section 5.2 while completing this problem.You may have noticed that when you compress the air in a bicycle pump, the body of the pump gets warmer. Assuming the pump and the air in it comprise the system, what is the sign of q, w, and ΔE when you compress the air?
Which of the following is true of a reaction in which ΔV is positive?a. ΔH = ΔEb. ΔH > ΔEc. ΔH < ΔE
The diagram shows four states of a system, each with different internal energy, E. In terms of the E values, which are the two expressions for the difference in internal energy between State A and State B?
The diagram shows four states of a system, each with different internal energy, E. Which expression(s) represent the difference in energy between State C and State D?
The diagram shows four states of a system, each with different internal energy, E. Suppose there is another state of the system, State E, and that its energy relative to State A is E = E1 + E4. Where would State E be on the diagram?
Why is the change in enthalpy usually easier to measure than the change in internal energy?
What is the value of ΔEDelta E if Efinal equals Einitial?
Three gas-phase reactions were run in a constant-pressure piston apparatus as shown in the following illustration. For each reaction, give the balanced reaction and predict the sign of w (the work done) for the reaction.If just the balanced reactions were given, how could you predict the sign of w for a reaction?
You may want to reference (Pages 177 - 178) Section 5.4 while completing this problem.In a constant-pressure process, ΔH = 0. What can you conclude about ΔE, q, and w?
Three gas-phase reactions were run in a constant-pressure piston apparatus as shown in the following illustration. For each reaction, give the balanced reaction and predict the sign of w (the work done) for the reaction.If just the balanced reactions were given, how could you predict the sign of w for a reaction?
Three gas-phase reactions were run in a constant-pressure piston apparatus as shown in the following illustration. For each reaction, give the balanced reaction and predict the sign of w (the work done) for the reaction.If just the balanced reactions were given, how could you predict the sign of w for a reaction?
The complete combustion of ethanol, C2H5OH(l), to form H2O(g) and CO2(g) at constant pressure releases 1235 kJ of heat per mole of C2H5OH. Draw the correct enthalpy diagram for the reaction.
Identify each energy exchange as primarily heat or work.a. A rolling billiard ball collides with another billiard ball. The first billiard ball (defined as the system) stops rolling after the collision.b. A book falls to the floor. (The book is the system).c. A father pushes his daughter on a swing. (The daughter and the swing are the system).
Nitrogen gas reacts with hydrogen gas to form ammonia gas . Consider the reaction between nitrogen and hydrogen as depicted below:a. Draw what the container will look like after the reaction has gone to completion. Assume a constant pressure of 1 atm.
Determine whether the sign of E is positive or negative for the system.a. A rolling billiard ball collides with another billiard ball. The first billiard ball (defined as the system) stops rolling after the collision.b. A book falls to the floor. (The book is the system).c. A father pushes his daughter on a swing. (The daughter and the swing are the system).
You may want to reference (Pages 166 - 172)Section 5.2 while completing this problem.A mixture of gases A2 and B2 are introduced to a slender metal cylinder that has one end closed and the other fitted with a piston that makes a gas-tight seal so that the gases are a closed system. The cylinder is submerged in a large beaker of water whose temperature is 25˚C, and a spark is used to trigger a reaction in the cylinder. At the completion of the reaction, the piston has moved downward, and the temperature of the water bath has increased to 28˚C. If we define the system as the gases inside the cylinder, which of the following best describes the signs of q, w, and ΔE for this reaction?(a) q < 0, w < 0, ΔE < 0(b) q < 0, w > 0, ΔE < 0(c) q < 0, w > 0, the sign of ΔE cannot be determined from the information given(d) q > 0, w > 0, ΔE > 0(e) q > 0, w < 0, the sign of ΔE cannot be determined from the information given
Consider the following changes: a. N2 (g) → N2 (l)b. CO (g) + H2O (g) → H2 (g) + CO2 (g)c. Ca3P2 (s) + 6 H2O (l) →  H2 (g) + CO2 (g)d. 2CH3OH (l) + 3O2 (g) → 2CO2 (g) + 4H2O (l)e. I2 (s) → I2 (g)At constant temperature and pressure, in which of these changes is work done by the system on the surroundings? By the surroundings on the system? In which of them is no work done?
Consider these fictitious internal energy gauges for a chemical system and its surroundings:Which diagram best represents the energy gauges for the same system and surroundings following an energy exchange in which ΔEsys is negative?
Identify each energy exchange as heat or work and determine whether the sign of heat or work (relative to the system) is positive or negative.(a) An ice cube melts and cools the surrounding beverage. (The ice cube is the system.)(b) A metal cylinder is rolled up a ramp. (The metal cylinder is the system.)(c) Steam condenses on skin, causing a burn. (The condensing steam is the system.)
Suppose that the gas-phase reaction 2NO(g) + O2(g) → 2NO2(g) were carried out in a constant-volume container at constant temperature.Would the measured heat change represent ΔH or ΔE?
Suppose that the gas-phase reaction 2NO(g) + O2(g) → 2NO2(g) were carried out in a constant-volume container at constant temperature.(a) Would the measured heat change represent ΔH or ΔE?(b) If there is a difference, which quantity is larger for this reaction?
Suppose that the gas-phase reaction 2NO(g) + O2(g) → 2NO2(g) were carri