1. Raymond Chang 10th edition Chapter 18
Chemistry
Raymond Chang
10th edition
Chapter 18
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2. Question 1 The entropy change for the surroundings is positive when heat is given off by the system at constant pressure.
A) True
B) False

3. Question 2 If a reaction can be written as a series of steps, then the sum of the enthalpy changes of the steps equals the enthalpy change of the overall reaction.
A) This statement is true because enthalpy is a state function.
B) This is a statement of Hess's Law.
C) This statement would be true if enthalpy was replaced by entropy or Gibb's free energy.
D) All of the above.

4. Question 3 Which of the following is false?
A) The free energy of formation of elements in their standard states is zero.
B) The enthalpy of formation of elements in their standard states is zero.
C) The standard entropy of elements in their standard states is zero.
D) Different allotropes of an element have different values of enthalpies of formation.

5. Question 4 If a reaction has a negative DH° and a positive DS°, then which of the following is true at equilibrium
A) K>1.
B) K<1.
C) K=1.
D) Cannot tell because DG° was not supplied.

6. Question 5 A spontaneous reaction
A) has an equilibrium constant greater than 1.
B) has a Gibb's free energy value less than zero.
C) causes an overall increase in the entropy of the universe.
D) all of the above

7. Question 6 A reaction has a positive enthalpy change and a positive entropy change. Which of the following will make it more spontaneous?
A) Adding a catalyst.
B) Increasing the temperature.
C) Decreasing the temperature.
D) None of the above.

8. Question 7 If the molar heat of fusion of a certain substance is 5000 J/mol and the entropy of fusion is 50 J/molK, then the melting temperature is
A) impossible to determine from the data.
B) 100 degrees Celsius.
C) -173 degrees Celsius.
D) -273 degrees Celsius.

9. Question 8 If a reaction has a standard Gibb's free energy change of kJ at 25 degrees Celsius, then the equilibrium constant for the reaction is
A) 2.96X10-18.
B) 0.96.
C) 1.04.
D) 3.38X1017.

10. Question 9 For any process at equilibrium the standard Gibb's free energy change is zero.
A) True
B) False

11. Question 10 The standard Gibb's free energy change for a reaction is -50. kJ. If the concentrations present are such that Q = 10, then the actual Gibb's free energy change at 298 K is
A) kJ.
B) kJ.
C) 5654 kJ.
D) 5754 kJ.

12. Question 11 Which of the following is not a spontaneous reaction?
A) 2Al(s) + 3H2SO4(aq) ® Al2(SO4)3(aq) + 3H2(g)
B) 2KBr(aq) + Pb(NO3)2(aq) ® 2KNO3(aq) + PbBr2(s)
C) CaBr2(aq) + H2SO4(aq) ® CaSO4(s) + 2HBr(g)
D) H+(aq) + OH-(aq) ® H2O(l)
E) CO32-(aq) + HSO4-(aq) ® HCO3-(aq) + SO42-(aq)

13. Question 12 Which should have a larger entropy?
A) ice
B) steam
C) distilled water
D) tap water
E) all are the same

14. Question 13 For which of the following processes will DS° be positive?
A) formation of water vapor from hydrogen and oxygen
B) formation of carbon dioxide from carbon monoxide and oxygen
C) synthesis of ammonia from hydrogen and nitrogen
D) decomposition of hydrogen iodide into hydrogen and iodine gas
E) none of the above

15. Question 14 Calculate the standard free energy change for the synthesis of 1 mol hydrogen bromide from hydrogen gas and bromine liquid at 25°C.
A) kJ/mol
B) kJ/mol
C) kJ/mol
D) kJ/mol
E) none of the above

16. Question 15 Choose the false statement:
A) If DH is positive and DS is negative, DG will always be positive.
B) If DH is negative and DS is positive, DG will always be negative.
C) If DH is negative and DS is negative, DG may be negative or positive.
D) If DH is positive and DS is positive, DG will always be positive.

17. Question 16 A reaction is spontaneous if
A) DH is negative.
B) DS is negative.
C) DG is negative.
D) all of the above.
E) none of the above.

18. Question 17 It is possible to make a chemical reaction non spontaneous by adding either reactant or product.
A) True
B) False

19. Question 18 The entropy of the Universe is conserved.
A) True
B) False

20. Question 19 Which is an example of a spontaneous process?
A) ice melts.
B) a liquid boils.
C) a solid sublimes.
D) sugar dissolves in water.
E) they are all spontaneous under specific conditions.

21. Question 20 Because formation of water from hydrogen and oxygen has a negative DG, a mixture of hydrogen gas and oxygen gas will spontaneously combust.
A) True
B) False

22. Answer Key – Chapter 18 A D C B E B C D A