Section 19.1-19.3
1. Define internal energy
2. What does q > 0 and w > 0 mean?
3. Define spontaneous process?
4. Can a reaction be spontaneous in one direction but not the other?
5. Predict whether each process is spontaneous as described, spontaneous in the reverse direction, or at
equilibrium: (a) Water at 40 °C gets hotter when a piece of metal heated to 150 °C is added. (b) Water at
room temperature decomposes into H2(g) and O2(g). (c) Benzene vapor, C6H6(g), at a pressure of 1 atm
condenses to liquid benzene at the normal boiling point of benzene, 80.1 °C.
6. Define reversible process
7. Define irreversible process
8. Define isothermal
9. Define entropy
10. What is the relationship between entropy and heat
11. Give equations 19.1 and 19.2
12. Define ΔSfusion
13. Elemental mercury is a silver liquid at room temperature. Its normal freezing point is -38.9 °C, and its molar
enthalpy of fusion is ΔHfusion = 2.29 kJ/mol. What is the entropy change of the system when 50.0 g of Hg(l)
freezes at the normal freezing point?
14. Define equation 19.3
15. Second law of thermodynamics
16. What does a reversible and irreversible process look like (19.4)
17. Define microstates
18. Define equation 19.5 and 19.6
19. Define translational motion
20. Define vibrational motion
21. Define rotational motion
22. In general, the number of microstates possible for a system increases with an increase in volume, an
increase in temperature, or an increase in the number of molecules because any of these changes increases
the possible positions and kinetic energies of the molecules making up the system.
23. We expect entropy to increase under what three conditions
24. Predict whether _S is positive or negative for each process, assuming each occurs at constant temperature:
a) H2O(l) H2O(g)
b) Ag+(aq) + Cl-(aq) AgCl(s)
c) 4 Fe(s) + 3 O2(g)  2 Fe2O3(s)
d) N2(g) + O2(g) 2 NO(g)
25. In each pair, choose the system that has greater entropy and explain your choice: (a) 1 mol of NaCl(s) or 1
mol of HCl(g) at 25 °C, (b) 2 mol of HCl(g) or 1 mol of HCl(g) at 25 °C, (c) 1 mol of HCl(g) or 1 mol of
Ar(g) at 298 K.
26. Define the 3rd law of thermodynamics
27. Which of the following processes are spontaneous and which are nonspontaneous: (a) the ripening of a
banana, (b) dissolution of sugar in a cup of hot coffee, (c) the reaction of nitrogen atoms to form N2
molecules at 25 °C and 1 atm, (d) lightning, (e) formation of CH4 and O2 molecules from CO2 and H2O at
room temperature and 1 atm of pressure?
28. (a) Can endothermic chemical reactions be spontaneous? (b) Can a process that is spontaneous at one
temperature be nonspontaneous at a different temperature?
29. Consider the vaporization of liquid water to steam at a pressure of 1 atm. (a) Is this process endothermic or
exothermic? (b) In what temperature range is it a spontaneous process? (c) In what temperature range is it a
nonspontaneous process? (d) At what temperature are the two phases in equilibrium?
30. Indicate whether each statement is true or false. (a) If a system undergoes a reversible process, the entropy
of the universe increases. (b) If a system undergoes a reversible process, the change in entropy of the system
is exactly matched by an equal and opposite change in the entropy of the surroundings. (c) If a system
undergoes a reversible process, the entropy change of the system must be zero. (d) Most spontaneous
processes in nature are reversible.
31. Consider a process in which an ideal gas changes from state 1 to state 2 in such a way that its temperature
changes from 300 K to 200 K. (a) Does the temperature change depend on whether the process is reversible
or irreversible? (b) Is this process isothermal? (c) Does the change in the internal energy, ΔE, depend on the
particular pathway taken to carry out this change of state?
32. Consider a system consisting of an ice cube. (a) Under what conditions can the ice cube melt reversibly? (b)
If the ice cube melts reversibly, is ΔE zero for the process?
33. Indicate whether each statement is true or false. (a) ΔS for an isothermal process depends on both the
temperature and the amount of heat reversibly transferred. (b) ΔS is a state function. (c) The second law of
thermodynamics says that the entropy of the system increases for all spontaneous processes.
34. The normal boiling point of Br2(l) is 58.8 °C, and its molar enthalpy of vaporization is ΔHvap = 29.6
kJ/mol. (a) When Br2(l) boils at its normal boiling point, does its entropy increase or decrease? (b)
Calculate the value of ΔS when 1.00 mol of Br2(l) is vaporized at 58.8 °C.
35. Indicate whether each statement is true or false. (a) The second law of thermodynamics says that entropy is
conserved. (b) If the entropy of the system increases during a reversible process, the entropy change of the
surroundings must decrease by the same amount. (c) In a certain spontaneous process the system undergoes
an entropy change of 4.2 J/K; therefore, the entropy change of the surroundings must be -4.2 J/K.
36. (a) What sign for ΔS do you expect when the volume of 0.200 mol of an ideal gas at 27 °C is increased
isothermally from an initial volume of 10.0 L? (b) If the final volume is 18.5 L, calculate the entropy change
for the process. (c) Do you need to specify the temperature to calculate the entropy change? Explain.
37. For the isothermal expansion of a gas into a vacuum, ΔE = 0, q = 0, and w = 0. (a) Is this a spontaneous
process? (b) Explain why no work is done by the system during this process. (c) What is the “driving force”
for the expansion of the gas: enthalpy or entropy?
38. Would each of the following changes increase, decrease, or have no effect on the number of microstates
available to a system: (a) increase in temperature, (b) decrease in volume, (c) change of state from liquid to
gas?
39. (a) What do you expect for the sign of ΔS in a chemical reaction in which two moles of gaseous reactants
are converted to three moles of gaseous products? (b) For which of the processes in Exercise 19.11 does the
entropy of the system increase?
40. Does the entropy of the system increase, decrease, or stay the same when (a) a solid melts, (b) a gas
liquefies, (c) a solid sublimes? and water are mixed to form a solution?
41. Indicate whether each statement is true or false. (a) The third law of thermodynamics says that the entropy
of a perfect, pure crystal at absolute zero increases with the mass of the crystal. (b) “Translational motion”
of molecules refers to their change in spatial location as a function of time. (c) “Rotational” and
“vibrational” motions contribute to the entropy in atomic gases like He and Xe. (d) The larger the number of
atoms in a molecule, the more degrees of freedom of rotational and vibrational motion it likely has.
42. For each of the following pairs, choose the substance with the higher entropy per mole at a given
temperature: (a) Ar(l) or Ar(g), (b) He(g) at 3 atm pressure or He(g) at 1.5 atm pressure, (c) 1 mol of Ne(g)
in 15.0 L or 1 mol of Ne(g) in 1.50 L, (d) CO2(g) or CO2(s).
43. Predict the sign of the entropy change of the system for each of the following reactions:
(a) N2(g) + 3 H2(g)  2 NH3(g)
(b) CaCO3(s)  CaO(s) + CO2(g)
(c) 3 C2H2(g)  C6H6(g)
(d) Al2O3(s) + 3 H2(g)  2 Al(s) + 3 H2O(g)