Ch. 17 - Chemical ThermodynamicsSee 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

Thermodynamics is the branch of physical science concerned with heat and its transformations to and from other forms of energy. 

Spontaneous & Nonspontaneous Reactions

Concept #1: Understanding Spontaneity

A reaction that requires no outside energy source is classified as a natural process and is spontaneous. 

A reaction that requires a continuous energy source to happen is classified as an unnatural process and is nonspontaneous. 

Practice: Which of the following statements is/are true?

a) The rusting of iron by oxygen is a non-spontaneous reaction.

b) The addition of a catalyst to a reaction increases spontaneity.

c) The movement of heat from a cold object to a hot object is a non-spontaneous reaction.

d) The diffusion of perfume molecules from one side of a room to the other is a non-spontaneous reaction.

e) None of the above. 

Additional Problems
What is true for the following reaction under standard condition? C2H6 (g) → C2H4 (g) + H2 (g) ΔH° is 137 kJ and ΔS° is 120 J/K a) spontaneous at all temperatures b) spontaneous only at high temperature c) spontaneous only at low temperature d) not spontaneous at all temperatures e) cannot be determined
Which is a state function (mark all that apply)? a) flame heating b) enthalpy c) entropy d) electrical work e) none of these
Which of the following is always positive when a spontaneous process occurs? a. ΔSsystem b. ΔSsurroundings c. ΔSuniverse d. ΔHuniverse e. ΔHsurroundings    
The sublimation of solid carbon dioxide is a spontaneous process. Predict the sign (+, -, or 0) of ∆Gº r , ∆Hº r , and ∆Sº r , respectively. 1. -, -, - 2. 0, +, + 3. -, 0, + 4. -, +, - 5. -, +, + 
Consider the equation carefully, and think about the sign of ∆S for the reaction it describes. NH4Br (s) → NH3 (g) + HBr (g) ∆H = +188.3 kJ. Which response describes the thermodynamic spontaneity of the reaction? 1. The reaction is spontaneous only at relatively high temperatures. 2. All responses are correct 3. The reaction is spontaneous at all temperatures. 4. The reaction is not spontaneous at any temperatures. 5. The reaction is spontaneous only at relatively low temperatures.
Which statement best describes spontaneous reactions? a) Spontaneous reactions occur very quickly b) Spontaneous reactions can proceed without any external input c) The reverse of a spontaneous reaction is also spontaneous reaction d) All spontaneous reactions are reversible reactions e) Most spontaneous reactions become less spontaneous at high temperatures
A mixture of hydrogen and chlorine remains unreacted until it is exposed to ultraviolet light from a burning magnesium strip. Then the following reaction occurs very rapidly: H2 + Cl2      →       2 HCl       ΔG = - 45.54 kJ                                               ΔH = - 44.12 kJ                                               ΔS = - 4.76 J/k Select the statement below which BEST explains this behavior. A. The reactants are thermodynamically more stable than the products. B. The reaction has a small equilibrium constant. C. The ultraviolet light raises the temperature of the system and makes the reaction more favorable. D. The negative value for ΔS slows down the reaction. E. The reaction is spontaneous by thermodynamics, but the reactants are kinetically stable.
Given the following reaction: A(g) ⇌ B(g), the forward reaction is spontaneous under standard conditions. Which of the following statements must be TRUE? I.                The reverse reaction is nonspontaneous under standard conditions. II.              A(g) will be completely converted to B(g) if sufficient time is allowed. III.             A(g) will be completely converted to B(g) rapidly.   A) none of these B) I and I C) I, II, and III D) I E) II and III
For the reaction A + B ⇌ C + D, ΔH°= +40 kJ and ΔS°= +50 J/K. Therefore, the reaction at standard conditions is A. spontaneous at temperatures less than 10 K. B. spontaneous at temperatures greater than 800 K. C. spontaneous only at temperatures between 10 K and 800 K. D. spontaneous at all temperatures. E. Nonspontaneous at all temperatures.
As O2 (l) is cooled at 1 atm, it freezes at 54.5 K to form Solid I. At a lower temperature, Solid I rearranges to Solid II, which has a different crystal structure. Thermal measurements show that ΔH for the I→II phase transition = -743.1 J/mol, and ΔS for the same transition = -17.0 J/K mol. At what temperature are Solids I and II in equilibrium? A. 2.06 K B. 43.7 K C. 31.5 K D. 53.4 K E. They can never be in equilibrium because they are both solids.
A reaction has a standard entropy change of +32.83 J/K and a standard enthalpy of +8.10 kJ. At what temperature is the reaction spontaneous? Assume the enthalpy and entropy of reaction are independent of temperature. a) Spontaneous when T > 246.7 K b) Spontaneous when T < 246.7 K c) Spontaneous when T > 25 K d) The reaction is non-spontaneous at all temperatures e) The reaction spontaneous at all times
Physical processes, including chemical reactions, tend to go towards ________ entropy and _________ energy.  The answers in order are (a) lower, higher       (b) higher, lower       (c) lower, lower       (d) higher, higher
Which reaction below is most likely spontaneous at any temperature? a. CH3CH2OH (g) → CH3CH2OH (I) b. 2 H2 (g) + O2 (g) → 2 H2O (g) c. C6H6O6 (s) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (I) d. CO2 (s) → CO2 (g) e. None of the above
What factor ultimately determines whether any physical process, including a chemical reaction, is spontaneous or not? a) the change in entropy of the components involved in the process b) the change in enthalpy of the components involved in the process c) the change in enthalpy of the universe d) the change in entropy of the universe e) the change in entropy of the world outside the process f) the change in enthalpy of the world outside the process
Consider the following facts: water freezes spontaneously at -5 °C and 1 atm, and ice has a more ordered structure than liquid water. Explain how a spontaneous process can lead to a decrease in entropy.
For the process O2 (g) → 2 O (g), ΔH ° = + 498 kJ. What would be predicted for the sign of ΔSrxn   and the conditions under which this reaction would be spontaneous? ΔSrxn                             Spontaneous             a)     positive            at low temperatures only             b)     positive            at high temperatures only             c)     negative           at high temperatures only             d)     negative           at low temperatures only
For which reaction, carried out at standard conditions, would both the enthalpy and entropy changes drive the reaction in the same direction? a) 2 H2 (g) + O2 (g) → 2 H2O (l)         ΔH = - 571.1 kJ b) 2 Na (s) + Cl2 (g) → 2 NaCl (s)      ΔH = - 822.0 kJ c) N2 (g) + 2 O2 (g) → 2 NO2 (g)        ΔH = + 67.7 kJ d) 2 NH3 (g) → N2 (g) + 3 H2 (g)        ΔH = + 92.4 kJ
Which of the following processes WILL NOT be spontaneous at 1000 K? A)        ΔH = +40.2kJ/mole      ΔS =  -41.8 J/mole K B)        ΔH = +40.2kJ/mole      ΔS =  +41.8 J/mole K C)        ΔH = -41.8 kJ/mole      ΔS =  +40.2 J/mole K D)        ΔH = +41.8 kJ/mole      ΔS =  -40.2 J/mole K E)         both A and D
When a liquid evaporates, which is true about the signs of the enthalpy and entropy changes? a) ΔH is positive, ΔS is postive b) ΔH is positive, ΔS is negative c) ΔH is negative, ΔS is positive d) ΔH is negative, ΔS is negative  
Which of the following is an example of a nonspontaneous process? A) ice melting at room temperature B) sodium metal reacting violently with water C) rusting of iron at room temperature D) a ball rolling downhill E) water freezing at room temperature
A spontaneous endothermic reaction always A) causes the surrroundings to get colder. B) bursts into flame. C) requires a spark to initiate it. D) releases heat to the surrroundings. E) results in an increase in ΔSsurr
The reaction rates of many spontaneous reactions are actually very slow. Which of these statements is the best explanation for this observation? A) Kp for the reaction is less than one. B) The activation energy of the reaction is large. C) ΔG° for the reaction is positive. D) Such reactions are endothermic. E) The entropy change is negative. 
Given that the normal freezing point of ammonia is -78°C. Predict the signs of ΔH, ΔS and ΔG for ammonia when it freezes at -80°C and 1 atm. NH3(l) → NH3(s)           ΔH        ΔS       ΔG A.         +         -         + B.         -         -         - C.         -         -         0 D.         -         +         - E.        +         +         0    
The combustion reactions of hydrocarbons are reactions where ΔH°< 0 and ΔS° > 0. Based on this information, which one of the following statements is true regarding these reactions? (a) At all T, K is < 1. (b) At all T, K is > 1. (c) At low T, K is < 1, but at high T, K is > 1. (d) At low T, K is > 1, but at high T, K is < 1. (e) Can’t determine from the information given.
The thermodynamic condition for a spontaneous process at constant T and P is A) ΔS > 0. B) ΔS < 0. C) ΔG < 0. D) ΔG > 0. E) ΔG° = 0.
Sodium carbonate can be made by heating sodium bicarbonate: 2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g). Given that ΔH° = 128.9 kJ/mol and ΔG° = 33.1 kJ/mol at 25°C, above what minimum temperature will the reaction become spontaneous under standard-state conditions? A) 0.4 K B) 3.9 K C) 321 K D) 401 K E) 525 K
If a process has a ΔH = +48 kJ/mol and a ΔS = -130 J/mol K at what T will it become spontaneous? A) 298 K B) 273 K C) 369 K D) 642 K E) Never  
Which of the following statements is TRUE? (a) An exothermic process will always be spontaneous. (b) A process in which the entropy of the system increases will always be spontaneous. (c) An endothermic process can never be spontaneous. (d) A process in which the entropy of the surroundings increases will always be spontaneous. (e) An exothermic process that is accompanied by an increase in the entropy of the system will always be spontaneous.
When barium hydroxide is dissolved in water, the temperature of the solution increases. Which of the following statements regarding this dissolution process is TRUE? (a) The reaction is spontaneous at all temperatures. (b) The reaction is driven only by entropy. (c) The reaction is driven only by enthalpy. (d) The reaction is spontaneous only at low temperatures. (e) The reaction is spontaneous only at high temperatures.
For the reaction A2(g) + B(s) → A2B(g) ΔH° > 0 and ΔS° > 0 Which of the following statements is true? A. The reaction is spontaneous at low temperatures. B. The reaction is spontaneous at all temperatures. C. ΔH° becomes more positive as temperature increases. D. The reaction is spontaneous at high temperatures. E. The reaction is non-spontaneous at all temperatures.
You observe that carbon dioxide sublimes. Which of the following statements about the signs of this process is/are true? I) Work (w) is positive. II) Heat (q) is negative. III) Change in Gibbs free energy (∆G) is positive. IV) Change in entropy (∆S) is positive. 1. I and II 2. II and III 3. I, II and III 4. I only 5. IV only  6. III and IV
For the reaction given below, ΔH° = -1516kJ and ΔS° = -432.8J/K at 25°C SiH4(g) + 2O2(g) →  SiO2(g) + 2H2O(l)  The reaction is spontaneous: a. only below a certain temperature b. only above a certain temperature c. at all temperatures d. at no temperatures e. cannot tell from the information available.    
Kw for the auto-ionization of water, H2O(l) → H+(aq) + OH− (aq), is 1.0 × 10−14. What are the signs (+/−) of ΔS° and ΔH° for the reaction at 25°C? a) ΔS° = (+) and ΔH° = (+) b) ΔS° = (+) and ΔH° = (−) c) ΔS° = (–) and ΔH° = (+) d) ΔS° = (–) and ΔH° = (–)
Consider the following sets. Which one indicates a  NON-spontaneous reaction. A. ΔH° = -35 kJ; ΔS° = 40 J/K; and the temperature is 80°C. B. ΔH° = -19 kJ; ΔS° = -60 J/K; and the temperature is 10°C. C. ΔH° = -15 kJ; ΔS° = -40 J/K; and the temperature is 150°C. D. ΔH° = 25kJ; ΔS° = 70 J/K; and the temperature is 125°C. E. ΔH° = 20 kJ; ΔS° = 75 J/K; and the temperature is 80°C.
Which of the following statements is TRUE? A) Entropy is not a state function. B) Endothermic processes are never spontaneous. C) Endothermic processes decrease the entropy of the surroundings, at constant T and P. D) Exothermic processes are always spontaneous. E) None of the above are true.
For the reaction 2 SO3(g) → 2 SO2(g) + O2(g) ∆H◦r = +198 kJ · mol−1 and ∆S◦r = 190 J · K−1 · mol−1 at 298 K. The forward reaction will be spontaneous at 1. temperatures above 1042 K.  2. temperatures below 1042 K. 3. all temperatures. 4. no temperature. 5. temperatures above 1315 K.
Consider a reaction that has a positive ΔH and a positive ΔS. Which of the following statements is TRUE? A) This reaction will be non-spontaneous only at high temperatures. B) This reaction will be non-spontaneous at all temperatures. C) This reaction will be spontaneous at all temperatures. D) This reaction will be spontaneous only at high temperatures. E) It is not possible to determine without more information.  
Solid ammonium nitrate is very soluble in water. When it dissolves, the solution becomes very cold. Based on this information alone, what are the most likely signs of ΔH ̊, ΔS ̊ and ΔG ̊? a) +, +, ‐ b) +, +, + c) +, ‐, ‐ d) ‐, ‐, ‐ e) ‐, +, ‐
Consider a 1.00 L solution of 0.150 M HCN (Ka = 4.9 * 10−10); Assume carbon is the central atom.  Indicate whether each statement is true or false.     A. There are more HCN molecules in the solution than CN− ions  B. The acid reaction (corresponding to Ka) would have a ΔG° < 0  C. Adding 0.150 moles of a strong base to this solution would make a buffer  D. HCN is polar and has a linear shape  E. The best Lewis structure would have a single bond and triple bond on C F. HCN would exhibit hydrogen bonds with water 
The following reaction is endothermic: 2 H2O (l) → 2 H2(g) + O2(g) Which of the following answers correctly describes the spontaneity: A. This reaction is always spontaneous B. This reaction is only spontaneous at low temperatures C. This reaction is only spontaneous at high temperatures D. This reaction is never spontaneous  
Ethane is C2H6. Consider the reaction below:  C2H6(g) ⇋ 2 Cgraphite(s) + 3 H2(g)  ∆G◦rxn = 7.86 kJ · mol−1 The decomposition of ethane is (spontaneous/non-spontaneous) and therefore ethane is (stable/unstable). 1. spontaneous, unstable 2. spontaneous, stable 3. non-spontaneous, unstable 4. non-spontaneous, stable  
Assuming the following ΔH°rxn and ΔS°rxn values are independent of temperature, which of reactions I, II, and III is/are spontaneous at 400°C? a) I b) II c) III d) I and II e) II and III
Which of the following is true of a general thermodynamic state function? 1. The change of the value of a state function is independent of the path of a process. 2. The value of a state function does NOT change with a change in temperature of a process. 3. The change in the value of a state function is always negative for a spontaneous reaction. 4. The value of the state function remains constant. 5. The change in the value of the state function is always positive for endothermic processes.
The plot of change in free energy versus temperature (T) shown below corresponds to a process that is enthalpically ________ (favored, disfavored) and entropically _______ (favored, disfavored). Explain.
Consider the reaction: 2O(g) → O2(g) a) Predict the signs of ΔH and ΔS. (There is no need to consult thermodynamic data tables).  b) Is the spontaneity of this reaction dependent on temperature? Explain.
Which of the following statements is TRUE?   a. State functions are not dependent on the path taken to reach a particular state. b. The change in the internal energy of a system can be determined by using constant volume calorimetry. c. Energy is neither created nor destroyed. d. The enthalpy of a reaction can be determined by using constant pressure calorimetry. e. All of the above statements are true. 
Above what temperature does the following reaction become spontaneous? FeO (s) + CO (g) CO2 (g) + Fe (g)                             ∆H = – 11.0 kJ ∆S = – 17.4 J/K   A. 191K B. 632K C. 298K D. Not enough information to determine E. Always spontaneous
When solid NH4NO3 is dissolved in water at 25°C, the temperature of the solution decreases. What is true about the signs of ΔH and ΔS for this process?  (A) ΔH is negative, ΔS is positive (B) ΔH is negative, ΔS is negative (C) ΔH is positive, ΔS is positive (D) ΔH is positive, ΔS is negative
For the reaction 2 SO3(g) → 2 SO2(g) + O2(g) ∆H◦r = +198 kJ·mol−1 at 298 K. Which statement is true for this reaction? 1. The reaction will not be spontaneous at any temperature. 2. The reaction will not be spontaneous at high temperatures. 3. ∆G◦r will be negative at high temperatures.  4. ∆G◦r will be positive at high temperatures. 5. The reaction is driven by the enthalpy.
The equilibrium constant for the reaction NH4Cl(s) → NH3(g) + HCl(g) is 1.1 × 10−16 at 25°C. If the equilibrium constant is 6.5 × 10 −2 at 300°C, which statement is correct? a) This is an enthalpy-driven reaction. b) The reaction is spontaneous at high temperatures. c) The reaction is spontaneous at all temperatures. d) The reaction is exothermic. e) The reaction is not spontaneous at any temperature.
The normal freezing point of ammonia is -78°C. Predict the signs of ∆H, ∆S, and ∆G for ammonia when it freezes at -80°C and 1 atm: NH3(l) → NH 3(s) 
For a reaction in which ΔH = 125 kJ/mol and ΔS = 325 J/K•mol, determine the temperature in Celsius above which the reaction is spontaneous. A.  385 °C             B.  273 °C       C.  112 °C       D.  405 °C       E.  25 °C  
For the reaction 2 C(s) + 2 H2(g) → C2H4(g)  ∆H°r = +52.3 kJ · mol−1 and ∆S°r =−53.07 J · K−1· mol−1 at 298 K. This reaction will be spontaneous at 1. no temperature.  2. temperatures below 985 K. 3. temperatures above 985 K. 4. temperatures below 1015 K. 5. all temperatures.  
Which of the following statements are true? I. In a spontaneous process, the path between reactants and products is reversible. II. The reaction of nitrogen atoms to form N2 molecules at 25° C and 1 atm is spontaneous. III. The melting of a solid is spontaneous above its melting point but nonspontaneous below its melting point. IV. The condensation of a liquid will be reversible if it occurs at any temperature other than the boiling point at a specified temperature. V. When a piece of metal is heated to 150° C and added to water, the fact that the water gets hotter is an example of a spontaneous process.    a) I, II, III b) II, III, IV c) II, III, V d) III, IV, V e) I, III, V  
Consider the conversion of a substance from solid to liquid. Solid ⇌ Liquid  At one atmosphere pressure and at the melting point of the substance, ________ . 
The following reaction is exothermic.                              N2 (g) + 3 H2 (g) → 2 NH3 (g) This means the reaction will be spontaneous in the forward direction at low temperature. is not spontaneous in the forward direction at any temperature. will be spontaneous in the forward direction at high temperature. is spontaneous in the forward direction at all temperatures.
The following reaction is endothermic:             2 H2O (l) → 2 H2 (g) + O2 (g) Which of the following answers correctly describes the spontaneity:             A.  This reaction is always spontaneous             B.  This reaction is only spontaneous at low temperatures             C.  This reaction is only spontaneous at high temperatures             D.  This reaction is never spontaneous
If a reaction is exothermic but experiences a decrease in its entropy, under what conditions is the reaction most likely to be spontaneous?   A. Low Temperature B. High Temperature C. Low Pressure D. High Pressure
For a certain chemical reaction,ΔH = 128 kJ/mol and ΔS = 64 J/ (mol × K) . What is the minimum temperature at which this reaction will be spontaneous?   A. 2 K                    B. 2000 K                     C. 2000 °C                     D. 2 °C
The reaction between elemental nitrogen and elemental hydrogen, shown below, is most kinetically and thermodynamically favorable.         N2 (g) + 3 H2 (g)   →    2 NH3 (g)  Based on this information, which of the following energy diagrams best describes this reaction? 
When ammonium ion and nitrate ion combine they form ammonium nitrate, NH4NO3. During this combination reaction the container feels cold to the touch. What are the signs for ∆H, ∆S, ∆G (at high T), and ∆G (low T)?     
Which of the following relationships must be true of any reaction at equilibrium? a) ∆Suniv = 0 b) ∆G ̊ = 0 c) ∆S ̊ = 0 d) Both a and b e) All of the above
Which of the following is required for a spontaneous reaction:   A. The entropy of the universe increases. B. The enthalpy of the universe increases. C. The Free Energy of the universe increases. D. The temperature of the universe increases. 
Which of the following is true regarding a non-spontaneous process:             I.    The process will occur with an outside influence             II.   The process will occur given sufficient time             III.  The process will never occur A.  only I         B.  only II       C.  both I and II          D.  only III      E.  None of the statements
Which reaction below is most likely spontaneous at any temperature?  a) CH3CH2OH (g) → CH3CH2OH (l) b) 2 H2 (g) + O2 (g) → 2 H2O (g) c) C6H6O6 (s) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (l) d) CO2 (s) → CO2 (g) e) None of the above
The process by which plants convert CO2 and H2O into C6H12O6 and O2 is called photosynthesis. This process is nonspontaneous, so energy must be provided to make the reaction occur, and that energy is provided by sunlight. “Chemosynthesis” refers to the biological conversion of simple carbon-containing molecules (e.g. CO2 or methane, CH4) into more complex energy-rich molecules using non-biological (inorganic) molecules as the energy source, rather than sunlight, as in photosynthesis. For example, giant tube worms found near deep-ocean sulfur vents contain bacteria that convert carbon dioxide to simple sugars using hydrogen sulfide as the energy source according to the chemical equation 12H2S + 6CO2 → C6H12O6 + 6H2O + 12S  A. Using the data provided below, calculate the following thermodynamic parameters for the above reaction.  1. ΔH°    2. ΔS°    3. ΔG°   B. Note the value you calculated for ΔG°. The normal expectation is that the reaction is spontaneous, but the calculations indicate that the reaction is nonspontaneous at 25°C.  At what temperature will the reaction become spontaneous?  When the reaction becomes spontaneous, will it be driven by enthalpy or entropy? 
A particular chemical reaction has a negative ΔH and a negative ΔS. Which statement is correct? (A) The reaction is spontaneous at all temperatures. (B) The reaction is non spontaneous at all temperatures. (C) The reaction becomes spontaneous as temperature increases. (D) The reaction becomes spontaneous as temperature decreases.
What can be said about an exothermic reaction with a negative entropy change? The reaction is a) spontaneous at all temperatures. b) spontaneous at high temperatures. c) spontaneous at low temperatures. d) spontaneous in the reverse direction at all temperatures. e) non-spontaneous in either direction at all temperatures.
The equilibrium constant of a certain reaction is experimentally determined at 200 K and 250 K and is found to be equal to 1010 and 1016, respectively. What can you say for certain about the reaction?1. nothing can be said for certain2. It is endothermic 3. It is exothermic4. It will become non-spontaneous at higher temperatures
For a chemical reaction to be spontaneous for standard conditions which of the following must be true? a) ΔH°rxn > 0 b) ΔS°rxn > 0 c) ΔG°rxn > 0 d) Both b and c e) None of the above
The compound benzoic acid, C6H5COOH, melts and 122.4°C. If the enthalpy of fusion of this compound is 17.3 kJ/mol, what is the entropy of the fusion.a) 31.3 J/(mol•K)b) 34.1 J/(mol•K)c) 38.0 J/(mol•K)d) 40.2 J/(mol•K)e) 43.8 J/(mol•K)
Which of the following are always true for a spontaneous process?I. ΔSsys > 0 II. ΔSsurr > 0 III. ΔSuniv > 0 IV. ΔGsys > 0a. Ib. IIc. IIId. I and IIIe. III and IV
For a particular reaction, ΔH°sys = 40 kJ and ΔS°sys = 50 J/K. Under what temperature parameters is the reaction spontaneous?a. When T < 10 K.b. When T > 800 K.c. At temperatures between 10 K and 800 K.d. The reaction is spontaneous at all temperatures.e. The reaction is not spontaneous at any temperature.
At constant pressure, the following reaction is exothermic. The reaction (as written) is2NO2(g) → N2O4(g)a. spontaneous at all temperatures.b. spontaneous at low temperatures but not a high temperature.c. spontaneous at high temperatures but not a low temperature.d. not spontaneous at any temperature.e. More information is required to answer the question.
Which is the best estimate for the boiling point of benzene (°C) given that ΔH° of vaporization is 31 kJ/mol and ΔS° of vaporization is 90 J/mol K?a.  25b.  45c.  65d.  15e.  5
Consider the following reaction at 120°C. Which statement must be true?H2O(l) → H2O(g)a. The reaction is not spontaneous.b. The reaction is spontaneous.c. ΔG = 0d. ΔG < 0e. Two of these statements are true.
The chemical reaction that causes chromium to corrode in air is given by:4Cr + 3O2 → 2Cr2O3In whichΔH°rxn = -2256 kJΔS°rxn = -549.1 J/KAt what temperature (Teq) do the forward and reverse corrosion reactions occur in equilibrium?Express your answer as an integer and include the appropriate units.
A particular chemical reaction has a negative ΔH and a positive ΔS. Which statement is correct? a) The reaction is spontaneous at all temperatures. b) The reaction is nonspontaneous at all temperatures. c) The reaction becomes spontaneous as temperature increases. d) The reaction becomes spontaneous as temperature decreases.
For bromine, ΔH ovap = 30.91 kJ/mol and ΔS ovap = 93.23 J K -1 mol-1 at 25 oC. What is the normal boiling point for bromine? a) 332 oCb) 25 oCc) 124 oCd) 58 oC
Which of the following reactions are spontaneous (favorable)? a) Reaction F b) Reaction E c) Reaction D d) Reaction C e) Reaction B f) Reaction A
Above what temperature does the following reaction become nonspontaneous?2 H2S(g) + 3 O2(g) → 2 SO2(g) + 2 H2O(g)H= -1036 kJ; S= -153.2 J/K 
For the chemical reaction, A → B, choose the combination that is correct.A) ΔG < 0; Q > KB) ΔG < 0; Q < KC) ΔG < 0; Q = KD) ΔG° < 0; Q = KE) ΔG° < 0; Q < K 
The temperature at which the following process reaches equilibrium at 1.0 atm is the normal boiling point of hydrogen peroxide. (R = 8.314 J•K-1•mol-1)H2O2(l) ⇌ H2O2(g)Use the following thermodynamic information at 298 K to determine this temperature.Substance:                H 2O2(l)              H2O2(g)ΔH°f (kJ/mol):             -187.7             -136.3ΔG°f (kJ/mol):             -120.4             -105.6S°   (J/K•mol):              109.6               232.7A) 120°CB) 144°CC) 196°CD) 418°CE) 585°C
Under standard conditions (298 K and 1 atm), which statement is true? i) diamond converts to graphite spontaneously ii) graphite converts to diamond spontaneously iii) none of the above
Which of the following reactions are spontaneous (favorable)? 
Sodium carbonate can be made by heating sodium bicarbonate:2 NaHCO3 (s) → Na2CO3(s) + CO2(g) + H2O(g)Given that standard enthalpy of reaction is 128.9 kJ and the standard Gibbs energy of reaction is 33.1 kJ at 25oC, above what temperature is the reaction become spontaneous? Assume that the enthalpy and entropy of reaction do not depend on temperature.a) 0.4 Kb) 3.9 Kc) 321 Kd) 401 Ke) 525 K
Above what temperature does the following reaction become nonspontaneous?FeO(s) + CO(g) → CO2 (g) + Fe(s)ΔH = -11.0 kJ; ΔS = -17.4 J/K  
Which of these processes is spontaneous?a) the combustion of natural gasb) a hot cup of tea cooling to room temperaturec) the extraction of iron metal from iron oreIdentify the system and the surroundings, and for each spontaneous process, the constraint that has been removed to allow the process to occur.
Which of the following is true regarding a non-spontaneous process: I. The process will occur with an outside influence II. The process will occur given sufficient time III. The process will never occur A. only I B. only II C. both I and II D. only III E. None of the statements
A reaction that is spontaneous as written _________. a. is very rapid b. will proceed without outside intervention c. is also spontaneous in the reverse direction d. has an equilibrium position that lies far to the left e. is very slow  
Which of the following processes are spontaneous? Select all that apply. a. a satellite falling to Earthb. water decomposing to H2 and O2 at 298 K and 1 atmc. average car prices increasingd. a soft-boiled egg becoming raw
Which of the following is always positive when a spontaneous process occurs? a. ΔSsystem b. ΔSsurroundings c. ΔSuniverse d. ΔHuniverse e. ΔHsurroundings
Which statement best describes the following endothermic reaction? C2H6(g) → C2H4(g) + H2(g) This reaction is ________. a. spontaneous at all temperatures b. spontaneous only at a high temperature c. spontaneous only at a low temperature d. nonspontaneous at all temperatures e. more information is needed to accurately describe the spontaneity of the reaction  
 Consider a reaction that has a positive ΔH and positive ΔS. Which of the following statements is TRUE?a. the reaction will be spontaneous at high tempsb. reaction will be spontaneous at all temps.c. reaction will be nonspontaneous at all temps.d. reaction will be nonspontaneous at high temps.e. not possible to determine without more information 
Above what temperature does the following reaction become non-spontaneous?H2S + 3O2 → 2SO2 + 2H2OΔH= -1036 kJΔS= -153.2 J/K
For the decomposition of ammonia to nitrogen and hydrogen, the equilibrium constant is 1.47 x 10-6 at 298 K. Calculate the temperature at which K = 0.01. For reaction, ΔH° = 92.38 kJ • mol-1.1. 390 K2. 59 K3. 117 K4. 241 K5. 468 K    • 
Based on the following graph below, determine the signs for enthalpy and entropy, respectively.  
A spontaneous chemical reaction is FAVORED by which of the following? a) increasing energy and increasing entropy b) lowering energy and increasing entropy c) increasing energy and decreasing entropy d) lowering energy and decreasing entropy
Which statement is true regarding the sublimation of dry ice (solid CO 2)?a. ΔH is positive, ΔS is negative, and ΔG is positive at all temperatures.b. ΔH is positive, ΔS is positive, and ΔG is positive at low temperature and negative at high temperature.c. ΔH is negative,ΔS is positive, and ΔG is negative at all temperatures.d. ΔH is negative, ΔS is negative, and ΔG is negative at low temperature and positive at high temperature.
What can be said about an Endothermic reaction with a negative entropy change? The reaction is a. spontaneous at all temperatures. b. spontaneous at high temperatures. c. spontaneous at low temperatures. d. spontaneous in the reverse direction at all temperatures. e. nonspontaneous in either direction at all temperatures.
Below what temperature does the following reaction become spontaneous?FeO(s) + CO(g)  → CO2(g) + Fe(g)    ∆H = -11.0kJ      ∆S = –17.4J/K191K632K298KNot enough information to determineAlways spontaneous
Fill in the blanks.
Select the statements below that are false and why.a) If a chemical reaction is spontaneous then the ΔS sys must always be positive.b) If a chemical reaction with a negative ΔS sys is spontaneous then ΔSsurr must be positive.c) If a chemical reaction is spontaneous then the ΔEuniv must be increasing.d) We don't need to worry about spontaneous reactions because they are rare.
Which of the reactions are spontaneous as written. Check all that apply.a. PbO2(s) + 4H+(aq) + Sn(s) → Pb2+(aq) + H2O(l) + Sn2+(aq)b. O2(g) + 2H2O(l) + Ag(s) → 4OH−(aq) + 4Ag+(aq)c. Br2(l) + 2I−(aq) → 2Br−(aq) + I2(s)
For the decomposition of calcium carbonate, consider the following thermodynamic data.ΔH∘rxn =178.5kJ/mol, ΔS∘rxn = 161.0J/(mol⋅K)Calculate the temperature in kelvins above which this reaction is spontaneous. Express your answer to four significant figures and include the appropriate units.
Which of these statements are true? 
If ΔH = -80.0 kJ and ΔS = -0.400 kJ/K, the reaction is spontaneous below a certain temperature. Calculate that temperature. Express your answer numerically in kelvins.
Making Methanol The element hydrogen is not abundant in nature, but it is a useful reagent in, for example, the potential synthesis of the liquid fuel methanol from gaseous carbon monoxide: 2 H2(g) + CO(g) --> CH3OH (g) This reaction is spontaneous at temperatures lower than:
Which of the following processes are spontaneous?a. Earth moving around the Sunb. A boulder rolling up a hillc. Sodium metal and chlorine gas reacting to form solid sodium chloride.
For a particular reaction, delta Hº is 55.4 kJ/mol and delta Sº is 94.1 J/(molK). Assuming these values change very little with temperature, over what temperature range is the reaction spontaneous in the forward direction? The reaction is spontaneous for temperatures less than greater than T = K.
What can be said about an endothermic reaction with a negative entropy change?The reaction is
The following generic reaction will always be spontaneous if the change in enthalpy is________ and the change in entropy is _________. negative, negativepositive, negative negative, positive positive, positive