Ch.6 - Thermochemistry WorksheetSee all chapters
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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
Jules Bruno

Endothermic and exothermic reactions

When covering thermochemistry, it’s also important to discuss the topics of endothermic solutions versus exothermic solutions. If we take a look at exothermic solutions, connected to these ideas are two variables - q and delta H. 

  • q is referred to as heat and delta 

  • H represents enthalpy. 

We need to remember that under constant pressure, we can say that q equals delta H. 

Exothermic reactions

If we’re saying exothermic here, that means that q would be negative in terms of its sign and delta H would also be negative. If we’re looking at any basic type of chemical reaction, we have AB + CD reactant that break down to form AD and BC as products. 

For an exothermic process or solution, we’re going to say that the bonds between the reactants are weak. That way they can break apart very easily and reform products that contain stronger bonds. For an exothermic process, reactants have weak bonds but products have stronger bonds. If we think about this in terms of this container here and let’s pretend it’s in solution. Let’s say we have energetic molecules that are bouncing all over the place. In an exothermic process, they’re going to release their heat. If they’re releasing their heat, they’re releasing energy. Eventually, they start to slow down because they’ve released a lot of energy. If they keep doing this, they release so much that they’ll slow down even more and connect together and form bonds. 

In an exothermic process, we release heat or energy to help form bonds. If these molecules are releasing heat, the water will pick up that heat. If I were to touch this container - this exothermic solution, the water has become warmer so when I touch it, it feels warm to the touch. So an exothermic process releases heat and my hand absorbs it. With exothermic processes, we have phase changes. We have gas, liquid and solid. A gas to a liquid is just condensation. A liquid to a solid is freezing. And then we can skip the liquid phase altogether and go straight from gas to solid which is deposition. 

Endothermic reactions

On the opposite side, we have endothermic processes. Here, the signs would be positive for q and delta H. We have our reactants and we have our products. Right now, the reactant bonds will be strong which means that energy needs to be used in order to break them down so that they can reform our products here. But here’s the thing. When we form those products, their bonds will be weak. 

Endothermic reactions in everyday life

Let’s think about this in terms of everyday life. We have ice. We have an ice cube. The water molecules are tightly packed. What happens if I start to heat up that ice cube? It’s going to melt. How does that happen? The water molecules inside the ice will absorb that thermal energy and use it to increase their kinetic energy enough so that they can push themselves apart and melt. We’re going to say an endothermic reaction absorbs heat in order to break its bonds. If I were to touch this endothermic process, it’s absorbing heat. It’s going to absorb warmth from my hand. An endothermic process feels cold to the touch.

Here with their phase changes we have solid to liquid which is melting or fancy term, fusion. Liquid to gas is vaporization. Then solid all the way to gas, that is just simply sublimation. 

Summary

Before we end, we need to realize the word fusion is tricky. With thermal chemistry, fusion just means melting. But when we start talking later on about nuclear chemistry, nuclear chemistry defines fusion as two basic radioactive particles combining together. It takes on an entirely different meaning. For thermochemistry, which we’re doing right now, fusion means melting. Later on with nuclear chemistry, it means the combining of different nuclei together. Just remember, it has two definitions. I know chemistry can be cruel but just remember that distinction.

Again, with thermal chemistry we have the idea of exothermic processes versus endothermic processes which are basically opposite processes. 


Jules Bruno

Jules felt a void in his life after his English degree from Duke, so he started tutoring in 2007 and got a B.S. in Chemistry from FIU. He’s exceptionally skilled at making concepts dead simple and helping students in covalent bonds of knowledge.


Additional Problems
Consider the combustion of fuel and the analogous reaction the food undergoes as part of the metabolic processes: fuel/food + O2(g) → CO2(g) + H2O(l) The reverse of this reaction that occurs during photosynthesis is also pretty important: CO2(g) + H2O(l) → fuel/food + O2(g)  Is this reaction endothermic or exothermic? Explain your reasoning. 
In an exothermic chemical reaction: A + 2 B → C When the amount of A and B reacting is doubled, what is expected to the amount of heat released?   A. No change in the amount of heat released B. The amount of heat released is two times the original C. The amount of heat released is four times the original D. The amount of heat released is eight times the original
How many of the following processes would be exothermic (ΔH < 0)? HCl(g) → H(g) + Cl(g) Br(g) + Br(g) → Br2(g) KI (s) → K + (g) + l  - (g) CO2(g) → CO(g) + O(g)   a) 0 b) 1 c) 2 d) 3 e) 4
Consider the process of 2 H(g) → H2(g) where ΔH = −436 kJ/mol Determine if the sentence below is true or false. Reacting two moles of H(g) would release 436 kJ.
Which of the following processes is endothermic? a) The freezing of water b) The combustion of gasoline c) The chemical reaction in a hot pack often used to treat sore muscles d) The vaporization of rubbing alcohol
When Na2S2O3• 3 H2O dissolves in water, the solution gets cold. Which diagram best represents the change in enthalpy for the contents of the flask?    
When a material in a liquid state is vaporized and then condensed to a liquid, the steps in the process are, respectively, a) exothermic and exothermic b) exothermic and endothermic  c) endothermic and exothermic d) endothermic and endothermic
Which of the following is an endothermic process?  (1) Chlorine gas expands while keeping a constant temperature. (∆E = 0) (2) Freezing gaseous carbon dioxide into dry ice at 194.7 K (3) Hydrogen peroxide decomposes to more stable products (4) An electric current breaks water down into H2 and O2
A reaction under certain conditions has an enthalpy change of ∆H = −118 kJ. This means that 118 kJ of heat would be liberated 1. if the reaction were carried out at constant pressure. 2. if the reaction were carried out at constant concentrations. 3. no matter how the reaction were carried out. 4. if the reaction were carried out in any type of calorimeter. 5. if the reaction were carried out at constant volume.
When solid ice, H2O(s), undergoes fusion a) The process is endothermic and heat is absorbed from the surroundings. b) The process is endothermic and heat is released to the surroundings. c) The process is exothermic and heat is released to the surroundings. d) The process is exothermic and heat is absorbed from the surroundings.
We have seen many times in lecture that heat is given off in the combustion of hydrogen gas. Which of the following is responsible for the heat? a. Breaking H-H and O-O bonds. b. Breaking O-H bonds. c. Forming H-H bonds and O-O bonds. d. Forming O-H bonds. e. Condensation of the water formed.
When diluting concentrated H2SO4, the acid should be added to water because (A) concentrated sulfuric acid is a strong acid and can only be added to water. (B) concentrated sulfuric acid is such a good oxidizing agent that it is able to oxidize water. (C) concentrated sulfuric acid must be protected from air by layer of water. (D) concentrated sulfuric acid and water generates considerable heat when in contact.
How many of the following processes require energy (absorbs heat)? Phase transition from solid to gas Freezing Increasing the temperature of water from 20 °C to 30 °C at 1 atm Melting ice A) 0                   B) 1                C) 2                  D) 3                 E) 4
How many of the following processes would be exothermic (ΔH < 0)? HCl (g)  →  H (g) + Cl (g) Br (g) + Br (g) → Br 2 (g) KI (s) → K + (g) + l  - (g) CO2 (g) → CO (g) + O (g)   a. 0 b. 1 c. 2 d. 3 e. 4
When dry ice, CO2 (s), sublimes to the gas phase to form CO 2 (g).   a. The process is endothermic and heat is absorbed from the surroundings b. The process is endothermic and heat is released to the surroundings c. The process is exothermic and heat is absorbed from the surroundings d. The process is exothermic and heat is released to the surroundings
Is the condensation of a gas an endothermic or exothermic process? ______________________
From a molecular viewpoint, where does the energy absorbed in an endothermic chemical reaction go?
Why does the reaction mixture undergo a decrease in temperature even though energy is absorbed?
If an endothermic reaction absorbs heat, then why does it feel cold to the touch?
Imagine a container placed in a tub of water, as depicted in the accompanying diagram. 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? From the systems perspective, is the process exothermic or endothermic?
Specific heat of water.Is the process shown in the figure endothermic or exothermic?
For a given process at constant pressure, H is positive. Is the process endothermic or exothermic?
Which of the following processes is exothermic?A) The formation of dew in the morning.B) The melting of ice.C) The chemical reaction in a "cold pack" often used treat injuries.D) The vaporization of water.E) None of the above are exothermic.
Classify each process as endothermic or exothermic. What is the sign of ΔH for each process? a. Gasoline burning in an engineb. Steam condensing on a mirrorc. Water boiling in a pot
Consider the process of 2 H(g) → H2(g) where ΔH = −436 kJ/molDetermine if the sentence below is true or false.The temperature of the surroundings would increase as this reaction proceeds.
Which one of the following processes is exothermic.a. H2(g) → 2H(g)b. 16CO2(g) +18H2O(l) → 2C8H18(l) + 25O2(g)c. H2(g) → H2O(l)d. CO2(s) → CO2(g)
Which of the reactions below is an exothermic reaction? A) H2O (I) → H2O (s) B) H2O (I) → H2O (g) C) HCl (aq) + NaOH (aq) → NaCl (aq) + HO (I) (Given that the solution warms upon reaction occuring) D) Both A and C E) Both B and C
Which of the following statements are true?a. ΔH for an endothermic reaction is positive.b. ΔH for an exothermic reaction is positive.c. When energy is transferred as heat from the system to surroundings, ΔH is negative.d. When energy is transferred as heat from the surroundings to the system, ΔH is negative.e. The evaporation of water is an exothermic process.f. Combustion reaction is exothermic.
Water vapor condensing to liquid water is what type of process? A) endothermic B) isotopic C) enthalpic D) exothermic 
Predict whether the following reactions will be exothermic or endothermic. 
 When heat is absorbed by the surroundings from the system, the process is said to be ______________ , and the sign of Δq is____________? (circle one)a.) exothermic, positiveb.) exothermic, negativec.) endothermic, positived.) endothermic, negative
A reaction under certain conditions has an enthalpy change of ΔH= -118kJ. This means that 118kJ of heat would be liberated:1. if the reaction were carried out at constant pressure.2. if the reaction were carried out at constant concentrations.3. no matter how the reaction were carried out.4. if the reaction were carried out in any type of container.5. if the reaction were carried out at constant volume.
Without referring to tables, predict which of the following has the higher enthalpy in each case: (a) 1 mol CO2 (s) or 1 mol CO2 (g) at the same temperature
Without referring to tables, predict which of the following has the higher enthalpy in each case: (b) 2 mol of hydrogen atoms or 1 mol of H2
Without referring to tables, predict which of the following has the higher enthalpy in each case: (c) 1 mol H2 (g) and 0.5 mol O2 (g) at 25°C or 1 mol H2O (g) at 25°C
Without referring to tables, predict which of the following has the higher enthalpy in each case: (d) 1 mol N2 (g) at 100°C or 1 mol N2 (g) at 300°C.
Consider the following reaction: CH3OH (g) → CO (g) + 2 H 2 (g)       ΔH = +90.7 kJ(a) Is heat absorbed or released in the course of this reaction?
Which of the following reactions are exothermic?
At one time, a common means of forming small quantities of oxygen gas in the laboratory was to heat KClO3:2 KClO3 (s) → 2 KCl (s) + 3 O2 (g)   ΔH = -89.4 kJThe decomposition of KClO3 proceeds spontaneously when it is heated. Do you think that the reverse reaction, the formation of KClO3 from KCl and O2, is likely to be feasible under ordinary conditions? Explain your answer. 
Consider the combustion of liquid methanol, CH 3OH (l):CH3OH (l) + 3/2 O2 (g) → CO2 (g) + 2 H2O (l)     ΔH = -726.5 kJ(a) What is the enthalpy change for the reverse reaction? Explain. 
Consider the combustion of liquid methanol, CH 3OH (l):CH3OH (l) + 3/2 O2 (g) → CO2 (g) + 2 H2O (l)     ΔH = -726.5 kJ(c) Which is more likely to be thermodynamically favored, the forward reaction or the reverse reaction? Explain.
Consider the combustion of liquid methanol, CH 3OH (l):CH3OH (l) + 3/2 O2 (g) → CO2 (g) + 2 H2O (l)     ΔH = -726.5 kJ(d) If the reaction were written to produce H2O (g) instead of H2O (l), would you expect the magnitude of ΔH to increase, decrease, or stay the same? Explain. 
What can you say about the reaction if the ratio of the C=C double bond strength to the C-C single bond strength is less that two?
Consider the decomposition of liquid benzene, C6H6 (l), to gaseous acetylene, C2H2 (g):C6H6 (l) → 3 C2H2 (g)         ΔH = +630 kJ(a) What is the enthalpy change for the reverse reaction? 
Consider the decomposition of liquid benzene, C6H6 (l), to gaseous acetylene, C2H2 (g):C6H6 (l) → 3 C2H2 (g)         ΔH = +630 kJ (c) Which is more likely to be thermodynamically favored, the forward reaction or the reverse reaction?
Consider the decomposition of liquid benzene, C6H6 (l), to gaseous acetylene, C2H2 (g):C6H6 (l) → 3 C2H2 (g)         ΔH = +630 kJ (d) If C6H6 (g) were consumed instead of C6H6 (l), would you expect the magnitude of ΔH to increase, decrease, or stay the same? Explain.
The reaction between hydrogen and oxygen to form water is highly exothermic. Which statement is true of the energies of the bonds that break and form during the reaction?a. The energy needed to break the required bonds is about the same as the energy released when the new bonds form.b. The energy needed to break the required bonds is less than the energy released when the new bonds form.c. The energy needed to break the required bonds is greater than the energy released when the new bonds form.
Which phase change, boiling or freezing of water, is exothermic? Explain.
Which of the following processes is exothermic?a. a candle flameb. the vaporization of waterc. melting of iced. the chemical reaction in a "cold pack" often used to treat injuriese. None of the above are exothermic
Which of the following processes is expected to be endothermic? a) combustion of a hydrocarbon b) freezing of liquid N2 at its normal melting point ( 53 K ) c) vaporization of zinc at its normal boiling point ( 1179 K) d) All of these are endothermic  e) None of these are endothermic
Which statement is FALSE?a. ΔErxn is a measure of heat.b. Endothermic has a positive ΔH.c. An exothermic reaction gives heat off to the surroundings.d. ΔHrxn is the heat of reaction.e. Enthalpy is the sum of a system's internal energy and the product of pressure and volume.
The formation of CsCl from Cs(s) and Cl 2(g) involves the following steps. Which of these steps absorb energy and which release energy?a. Cs(s) → Cs(g)b. 1/2Cl2(g) → Cl(g)c. Cs(g) → Cs+(g )+ e-d. Cl(g) + e- → Cl-(g)e. Cs+(g) + Cl-(g) → CsCl(s)
Which of the following is true of an endothermic reaction?a. Strong bonds break and weak bonds form: this means that more energy is released than absorbed. b. Weak bonds break and strong bonds form: this means that more energy is released than absorbed.c. The bonds that break and those that form are of approximately the same strength.d. Strong bonds break and weak bonds form: this means that more energy is absorbed than released.e. Weak bonds break and strong bonds form: this means that more energy is absorbed than released.
What is the sign of ΔH for the process depicted in the figure above?
For each of the following reactions, predict the sign of ΔH˚.(i) 2 Mg(s) + O2 (g) ⇌ 2 MgO(s)(ii) 2 KI(s) ⇌ 2 K(g) + I2(g)(iii) Na2(g) ⇌ 2 Na(g)(iv) 2 V2O5(s) ⇌ 4 V(s) + 5O2(g)
Draw an enthalpy diagram for a general endothermic reaction; label the axis, reactants, products, and ΔH with its sign.
You may want to reference (Pages 816 - 821) Section 19.3 while completing this problem.Predict the sign of ΔH accompanying this reaction on the figure.
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.Which of these processes is endothermic?
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 of CH4(g). Which is the more endothermic process?
Predict whether the following reactions will be exothermic or endothermic.a. N2(g)+3H2(g) → 2NH3b. S(g)+O2(g) → SO2(g)c. 2H2O(g) → 2H2(g) + O2(g)d. 2F(g) → F2(g)
Which process is endothermic?a) the evaporation of water from the skinb) the burning of candle waxc) the oxidation of iron in a chemical hand warmerd) the combustion of natural gas in a stove
Sort the following reactions as either endothermic or exothermic.a. making popcorn in a microwave oven b. a burning match c. the reaction inside a chemical heat pack d. boiling water e. burning rocket fuel 
When ammonium chloride (NH4Cl) is dissolved in water, the solution becomes colder. Is the dissolution of ammonium chloride endothermic or exothermic?
5.82Without doing any calculations, predict the sign of ΔH for each of the following reactions:(d) HBr(g) → H(g) + Br(g)
5.81Without doing any calculations, predict the sign of ΔH for each of the following reactions:(b) 2H(g) → H2(g)
5.81Without doing any calculations, predict the sign of ΔH for each of the following reactions:(c) Na(g) → Na+(g) + e-
Identify each process as endothermic or exothermic and indicate the sign of ΔH.(a) an ice cube melting(b) nail polish remover quickly evaporating after it is accidentally spilled on the skin(c) gasoline burning within the cylinder of an automobile engine
Name the phase transition in each of the following situations, and indicate whether it is exothermic or endothermic:Wet clothes dry on a warm summer day.
You may want to reference (Pages 450 - 453) Section 11.4 while completing this problem.Name the phase transition in each of the following situations, and indicate whether it is exothermic or endothermic(a) Bromine vapor turns to bromine liquid as it is cooled.(b) Crystals of iodine disappear from an evaporating dish as they stand in a fume hood.(c) Rubbing alcohol in an open container slowly disappears.(d) Molten lava from a volcano turns into solid rock.
You may want to reference (Pages 450 - 453) Section 11.4 while completing this problem.Ethyl chloride (C2H5Cl) boils at 12˚C. When liquid C2H5Cl under pressure is sprayed on a room-temperature (25˚C) surface in air, the surface is cooled considerably. What does this observation tell us about the enthalpy of C2H5Cl(g) as compared with the enthalpy of C2H5Cl(l)?
Ethyl chloride (C2H5Cl) boils at 12 oC. When liquid C2H5Cl under pressure is sprayed on a room-temperature (25 oC) surface in air, the surface is cooled considerably.Assume that the heat lost by the surface is gained by ethyl chloride. What enthalpies must you consider if you were to calculate the final temperature of the surface?
Both graphite and diamond burn.C(s, diamond) + O2(g) ⟶ CO2(g)For the conversion of graphite to diamond:C(s, graphite) → C(s, diamond)                 ΔH° 298 = 1.90 kJWhich produces more heat, the combustion of graphite or the combustion of diamond?
Classify each process as endothermic or exothermic.a. gasoline burning in an engineb. steam condensing on a mirrorc. water boiling in a pot
What is the sign of ΔH for each process.a. gasoline burning in an engineb. steam condensing on a mirrorc. water boiling in a pot
A reaction takes place in a steel vessel within a chamber filled with argon gas. Shown below are atomic-scale views of the argon adjacent to the surface of the container wall of the reaction vessel before and after the reaction. Was the reaction exothermic or endothermic? Explain.
Determine whether each of the following is exothermic or endothermic.a. natural gas burning on a stoveb. isopropyl alcohol evaporating from skinc. water condensing from steam
Determine whether each of the following is exothermic or endothermic.dry ice evaporating,a sparkler burning, andthe reaction that occurs in a chemical cold pack often used to ice athletic injuries.
Indicate the sign of ΔH for the following processes.dry ice evaporating,a sparkler burning, andthe reaction that occurs in a chemical cold pack often used to ice athletic injuries.
Without doing any calculations, predict the sign of ΔH for each of the following reactions:(a) NaCl(s) → Na+(g) + Cl-(g)
Without doing any calculations, predict the sign of ΔH for each of the following reactions:(a) 2NO2(g) → N2O4(g)
Consider the combustion of liquid methanol, CH3 OH(l): CH3OH(l) + 3/2 O2(g) → CO2(g) + 2 H2O(l), ΔH = –726.5kJIf the reaction were written to produce H2O(g) instead of H2O(l), would you expect the magnitude of ΔH to increase, decrease, or stay the same?
Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels. Which fuel contains the most energy in the least mass?
Are the following processes exothermic or endothermic?d. Water is boiled in a teakettle.
Are the following processes exothermic or endothermic?b. Natural gas (CH4) is burned in a furnace.
Are the following processes exothermic or endothermic?b. water condensing on a cold pipe
Are the following processes exothermic or endothermic?a. the combustion of gasoline in a car engine
Calculate ΔE and determine whether the process is endothermic or exothermic for the following cases: (a) q = 0.763 kJ and w = -840 J. 
Consider the following balanced thermochemical equation for a reaction sometimes used for H2S production:1/8S8 (s) + H2 (g) ⟶ H2S (g)                 ΔH = −20.2 kJIs this an exothermic or endothermic reaction?
Consider the following balanced thermochemical equation for the decomposition of the mineral magnesite:MgCO3 (s) ⟶ MgO (s) + CO2 (g)                         ΔH = 117.3 kJIs heat absorbed or released in the reaction?
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 of CH4(g). Calculate the enthalpy change in each case. What accounts for the difference in ΔH values?
When H2(g) and O2(g) react to form H2O(l), heat is released to the surroundings. Consider the reverse reaction, namely, the formation of H2(g) and O2(g) from H2O(l): 2 H2O(l) → 2 H2(g) + O2(g). Is this reaction exothermic or endothermic?
Consider the following reaction:2Mg(s) + O2 (g) → 2MgO(s)  ΔH = - 1204 kJIs this reaction exothermic or endothermic?
You may want to reference (Pages 172 - 176)Section 5.3 while completing this problem.Consider the following reaction: 2 CH3OH(g)  →  2CH4(g) + O2 (g), ΔH = +252.8 kJIs this reaction exothermic or endothermic?
When a 4.25-g sample of solid ammonium nitrate dissolves in 60.0 g of water in a coffee-cup calorimeter, the temperature drops from 22.0 oC to 16.9 oC.You may want to reference (Pages 179 - 183) Section 5.5 while completing this problem.Calculate ΔH (in kJ/mol NH4NO3) for the solution process:NH4NO3(s) → NH4+(aq) + NO3-(aq)Assume that the specific heat of the solution is the same as that of pure water.Is this process endothermic or exothermic?
Classify the following phase changes as endothermic or exothermic.
5.82Without doing any calculations, predict the sign of ΔH for each of the following reactions:(b) 2F(g) → F2(g)
Classify each process as an endothermic or exothermic process.1. forming solute-solvent attractions2. breaking solute-solute attractions3. breaking solvent-solvent attractions
In which of the following processes will energy be evolved as heat?a. sublimationb. crystallizationc. vaporizationd. meltinge. none of these
Explain the following observations:(b) Perspiring is a mechanism for cooling the body.
A chemical reaction that gives off heat to its surroundings is said to be ____________ and has a ____________ value of H.
When a reaction occurs in a flask, you notice that the flask gets colder. What is the sign of ΔHDelta {H}?
Draw an enthalpy diagram for a general exothermic reaction; label the axis, reactants, products, and ΔH with its sign.
Which of the following processes are exothermic?a. N2 (g) → 2N (g)b. H2O (l) → H2O (s)c. Cl2 (g) → 2Cl (g)d. 2H2 (g) + O2 (g) → 2H2O (g)e. O2 (g) → 2O (g)
In an exothermic reaction, the reactants lose energy and the reaction feels hot to the touch. Explain why the reaction feels hot even though the reactants are losing energy. Where does the energy come from?
Indicate the sign of ΔH for the following processes.a. natural gas burning on a stoveb. isopropyl alcohol evaporating from skinc. water condensing from steam
Why is melting ice an endothermic reaction?
Explain the difference between endothermic reactions and exothermic reactions with respect to the bond energies of the bonds broken and formed.
A chemical reaction absorbs heat from the surroundings. Therefore it is _________ and has a ________ value of ΔH.A. endothermic, negative B. endothermic, positive C. isothermic (i.e. no change in temperature), zero D. exothermic, positive E. exothermic, negative
Given w = 0, an endothermic reaction has which of the following:a. +ΔH and +ΔEb. -ΔH and -ΔEc. +ΔH and -ΔEd. -ΔH and +ΔE
Which one of the following processes is endothermic?a. 2 H2 (g) + O2 (g) → 2 H2O (g)b. H2O (g) → H 2O (l)c. CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (g)d. H2O (s) → H2O (l)e. 2 Al (s) + Fe2O3 (s) → Al2O3 (s) + 2 Fe (s)
Which process is endothermic?a. The burning of candle wax.b. The combustion of natural gas in a stove.c. The formation of a chemical bond.d. The melting of ice.
Based on their descriptions, classify these chemical changes as endothermic or exothermic.
Is deposition endothermic or exothermic?
Predict whether the following reactions will be exothermic or endothermic.a. N2(g) + 3H2(g) → 2NH3(g)b. S(g) + O2(g) → SO2(g)c. 2H2O(g) → 2H2(g) + O2(g)d. 2F(g) → F2(g)
Sort the following reactions as either endothermic or exothermic. Explain your answer briefly.
Identify each of the following processes as endothermic or exothermic and indicate the sign of ∆H.a) ice cube meltingb) water freezing in a freezerc) wood burning in a fire
Consider the vaporization of liquid water to steam at a pressure of 1 atm.Is this process endothermic or exothermic?
Which of these physical changes would require the liberation of energy, exothermic?a. melting pointb. boiling pointc. condensation of steam to form liquidd. sublimation from a solid to a gas
Which one of the following is an endothermic process?A) ice meltingB) water freezingC) boiling soupD) Hydrochloric acid and barium hydroxide are mixed at 25 °C: the temperature increases.E) Both A and C
Which produces more heat, Os(s) + 2O2(g) ⟶ OsO4(s) or Os(s) + 2O2(g) ⟶ OsO4(g)? For the phase change OsO4(s) ⟶ OsO4(g),    ΔH = 56.4 kJ
Are the following processes exothermic or endothermic?a. When solid KBr is dissolved in water, the solution gets colder.
Which of the following is true if an exothermic reaction occurs out in a coffee-cup calorimeter?A. ΔH of the reactants is lower than ΔH of the products B. ΔH of the products is lower than ΔH of the reactants C. ΔH of the reactants is higher than ΔH of the products D. ΔH of the products is higher than ΔH of the reactants E. Two of the above
When 2 moles of C2H6 (g) react with O2 (g) to form CO2 (g) and H2O (g) according to the following equation, 2.86 x 103 kJ of energy are evolved. 2C2H6 (g) + 7O2 (g) → 4CO2 (g) + 6H2O(g) Is this reaction endothermic or exothermic? What is the value of q?
Ethyl chloride (boiling point, 13 °C) is used as a local anesthetic. When the liquid is sprayed on the skin, it cools the skin enough to freeze and numb it. Explain the cooling effect of liquid ethyl chloride.
Are the following processes exothermic or endothermic?d. F2 (g) → 2F (g)