Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
160 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 15
⌬G system ϭ Ϫ81,000 J Ϫ (Ϫ69,400 J)
⌬G system ϭ Ϫ12,000 J, or Ϫ12 kJ
Because ⌬G system is negative, the reaction is spontaneous.
Practice Problems
14. Calculate ⌬G system for each process, and state if the process is
spontaneous or nonspontaneous.
a. ⌬H system ϭ 147 kJ, T ϭ 422 K, ⌬S system ϭ Ϫ67 J/K
b. ⌬H system ϭ Ϫ43 kJ, T ϭ 21°C, ⌬S system ϭ Ϫ118 J/K
c. ⌬H system ϭ 227 kJ, T ϭ 574 K, ⌬S system ϭ 349 J/K
15. If ⌬G system ϭ 0, a reaction is in a state of chemical equilibrium,
in which the forward reaction and the reverse reaction occur
at equal rates. At what temperature is a reaction at chemical
equilibrium if ⌬H system ϭ Ϫ75 kJ and ⌬S system ϭ Ϫ192 J/K?
Chapter 15 Review
16. A sample of ethanol and a sample of aluminum have the same
mass. Which sample absorbs more energy as it is heated from
25°C to 56°C? Explain your answer.
17. What do the terms system, surroundings, and universe mean in
thermochemistry?
18. Describe two changes of state for which ⌬H is positive and two
changes of state for which ⌬H is negative.
19. Explain what is meant by the standard heat of formation of
ethane gas, (C 2 H 6 ). Include in your explanation the equation for
the formation of ethane.
20. For each of the following processes, the signs of ⌬H system and
⌬S system are known. Explain whether you have sufficient
information to determine whether each process is spontaneous.
a. ⌬H system Ͼ 0, ⌬S system Ͻ 0
b. ⌬H system Ͻ 0, ⌬S system Ͻ 0
c. ⌬H system Ͻ 0, ⌬S system Ͼ 0
160 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 15
⌬G system ϭ Ϫ81,000 J Ϫ (Ϫ69,400 J)
⌬G system ϭ Ϫ12,000 J, or Ϫ12 kJ
Because ⌬G system is negative, the reaction is spontaneous.
Practice Problems
14. Calculate ⌬G system for each process, and state if the process is
spontaneous or nonspontaneous.
a. ⌬H system ϭ 147 kJ, T ϭ 422 K, ⌬S system ϭ Ϫ67 J/K
b. ⌬H system ϭ Ϫ43 kJ, T ϭ 21°C, ⌬S system ϭ Ϫ118 J/K
c. ⌬H system ϭ 227 kJ, T ϭ 574 K, ⌬S system ϭ 349 J/K
15. If ⌬G system ϭ 0, a reaction is in a state of chemical equilibrium,
in which the forward reaction and the reverse reaction occur
at equal rates. At what temperature is a reaction at chemical
equilibrium if ⌬H system ϭ Ϫ75 kJ and ⌬S system ϭ Ϫ192 J/K?
Chapter 15 Review
16. A sample of ethanol and a sample of aluminum have the same
mass. Which sample absorbs more energy as it is heated from
25°C to 56°C? Explain your answer.
17. What do the terms system, surroundings, and universe mean in
thermochemistry?
18. Describe two changes of state for which ⌬H is positive and two
changes of state for which ⌬H is negative.
19. Explain what is meant by the standard heat of formation of
ethane gas, (C 2 H 6 ). Include in your explanation the equation for
the formation of ethane.
20. For each of the following processes, the signs of ⌬H system and
⌬S system are known. Explain whether you have sufficient
information to determine whether each process is spontaneous.
a. ⌬H system Ͼ 0, ⌬S system Ͻ 0
b. ⌬H system Ͻ 0, ⌬S system Ͻ 0
c. ⌬H system Ͻ 0, ⌬S system Ͼ 0