Burdge/Overby, Chemistry: Atoms First, 2e Ch14 | Page 29

598

CHAPTE R 14? Entropy and Free Energy

2F(g) at
V
C 14.2 Now consider the reaction F2(g)
constant temperature and pressure. What factors
contribute to the entropy increase associated with the
reaction?

Molar
Increased
Increase in
Volume
mass
number of
Phase
molecular
increase increase molecules change complexity
(i)
(ii)
(iii) (iv)
(v)
(a) i and iii
(b) i, ii, and iii
(c) i, iv, and v
V
C 14.3 Which of the following best describes why entropy
always increases with temperature?
(a) As temperature increases, the number of molecules
increases.
(b) As temperature increases, energy levels become
more closely spaced.
(c) As temperature increases, the molecules become
more energetic and can access more energy levels.
V
C 14.4 Which of the following best explains why entropy
typically increases with molar mass?
(a) As molar mass increases, the number of molecules
increases.
(b) As molar mass increases, energy levels become
more closely spaced.
(c) As molar mass increases, the molecules become
more energetic and can access more energy levels.
Review Questions
14.8 How does the entropy of a system change for each of
the following processes?
(a) A solid melts.
(b) A liquid freezes.
(c) A liquid boils.
(d) A vapor is converted to a solid.
(e) A vapor condenses to a liquid.
(f) A solid sublimes.
(g) A solid dissolves in water.
14.9 How does the entropy of a system change for each of
the following processes?
(a) Bromine liquid vaporizes.
(b) Water freezes to form ice.
(c) Naphthalene, the key component of mothballs,
sublimes.
(d) Sugar crystals form from a supersaturated solution.
(e) A block of lead melts.
(f) Iodine vapor condenses to form solid iodine.
(g) Carbon tetrachloride dissolves in liquid benzene.
14.10 Predict whether the entropy change is positive or
negative for each of the following reactions. Give
reasons for your predictions.
2KClO3(s) + O2(g)
(a) 2KClO4(s)
(b) H2O(g)
H2O(l)
(c) 2Na(s) + 2H2O(l)
2NaOH(aq) + H2(g)
(d) N2(g)
2N(g)

bur11184_ch14_570-603.indd 598

14.11 State whether the sign of the entropy change expected
for each of the following processes will be positive or
negative, and explain your predictions.
(a) PCl3(g) + Cl2(g)
PCl5(g)
(b) 2HgO(s)
2Hg(l) + O2(g)
(c) H2(g)
2H(g)
(d) U(s) + 3F2(g)
UF6(s)
Computational Problems
14.12 Calculate ?Ssys for (a) the isothermal expansion of
2.0 moles of an ideal gas from 10.0 L to 15.0 L, (b) the
isothermal expansion of 1.5 moles of an ideal gas from
20.0 L to 22.5 L, and (c) the isothermal compression of
5.0 moles of an id eal gas from 100.0 L to 75.0 L.
14.13 Calculate ?Ssys for (a) the isothermal compression of
0.0050 mole of an ideal gas from 112 mL to 52.5 mL,
(b) the isothermal compression of 0.015 mole of
an ideal gas from 225 mL to 22.5 mL, and (c) the
isothermal expansion of 22.1 moles of an ideal gas
from 122 L to 275 L.
14.14 Using the data in Appendix 2, calculate the standard
entropy changes for the following reactions at 25°C:
(a) S(rhombic) + O2(g)
SO2(g)
(b) MgCO3(s)
MgO(s) + CO2(g)
4CO2(g) + 6H2O(l)
(c) 2C2H6(g) + 7O2(g)
14.15 Using the data in Appendix 2, calculate the standard
entropy changes for the following reactions at 25°C:
(a) H2(g) + CuO(s)
Cu(s) + H2O(g)
(b) 2Al(s) + 3ZnO(s)
Al2O3(s) + 3Zn(s)
(c) CH4(g) + 2O2(g)
CO2(g) + 2H2O(l)
Conceptual Problems
14.16 For each pair of substances listed here, choose the
one having the larger standard entropy value at 25°C.
The same molar amount is used in the comparison.
Explain the basis for your choice. (a) Li(s) or Li(l),
(b) C2H5OH(l) or CH3OCH3(l) (Hint: Which molecule
can hydrogen bond?), (c) Ar(g) or Xe(g), (d) CO(g) or
CO2(g), (e) O2(g) or O3(g), (f) NO2(g) or N2O4(g).
14.17 Arrange the following substances (1 mole each)
in order of increasing entropy at 25°C: (a) Ne(g),
(b) SO2(g), (c) Na(s), (d)?NaCl(s), (e) H2(g). Give the
reasons for your arrangement.

Section 14.4:?Entropy Changes in the
Universe
Review Questions
14.18 State the second law of thermodynamics in words, and
express it mathematically.
14.19 State the third law of thermodynamics in words, and
explain its usefulness in calculating entropy values.
Computational Problems
14.20 Calculate ?Ssurr for each of the reactions in Problem
14.16 and determine if each reaction is spontaneous at
25°C.
14.21 Calculate ?Ssurr for each of the reactions in Problem
14.17 and determine if each reaction is spontaneous at
25°C.

9/10/13 12:01 PM