Chapter 19

(a) What is meant by calling a process irreversible? (b) After a particular irreversible process, the system is restored to its original state. What can be said about the condition of the surroundings after the system is restored to its original state? (c) Under what conditions will the condensation of a liquid be an irreversible process?

Consider a process in which an ideal gas changes from state 1 to state 2 in such a way that its temperature changes from $300\mathrm{K}$ to $200\mathrm{K}$. (a) Describe how this change might be carried out while keeping the volume of the gas constant. (b) Describe how it might be carried out while keeping the pressure of the gas constant. (c) Does the change in $\mathrm{\Delta }E$ depend on the particular pathway taken to carry out this change of state? Explain.

A system goes from state 1 to state 2 and back to state 1 . (a) What is the relationship between the value of $\mathrm{\Delta }E$ for going from state 1 to state 2 to that for going from state 2 back to state $1?$ (b) Without further information, can you conclude anything about the amount of heat transferred to the system as it goes from state 1 to state 2 as compared to that upon going from state 2 back to state $1?(\mathrm{c})$ Suppose the changes in state are reversible processes. Can you conclude anything about the work done by the system upon going from state 1 to state 2 as compared to that upon going from state 2 back to state $1?$

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 $\mathrm{\Delta }E$ zero for the process? Explain.

Consider what happens when a sample of the explosive TNT (Section 8.8: "Chemistry Put to Work: Explosives and Alfred Nobel") is detonated under atmospheric pressure. (a) Is the detonation a spontaneous process? (b) What is the sign of $q$ for this process? (c) Can you determine whether $w$ is positive, negative, or zero for the process? Explain. (d) Can you determine the sign of $\mathrm{\Delta }E$ for the process? Explain.

(a) How can we calculate $\mathrm{\Delta }S$ for an isothermal process? (b) Does $\mathrm{\Delta }S$ for a process depend on the path taken from the initial state to the final state of the system? Explain.

Suppose we vaporize a mole of liquid water at ${25}^{\circ }\mathrm{C}$ and another mole of water at $100{}^{\circ }\mathrm{C}$. (a) Assuming that the enthalpy of vaporization of water does not change much between ${25}^{\circ }\mathrm{C}$ and ${100}^{\circ }\mathrm{C},$ which process involves the larger change in entropy? (b) Does the entropy change in either process depend on whether we carry out the process reversibly or not? Explain.

The normal boiling point of ${\mathrm{Br}}_2(l)$ is $58.8{}^{\circ }\mathrm{C},$ and its molar enthalpy of vaporization is $\mathrm{\Delta }{H}_{\text{vap }}=29.6\mathrm{kJ}/$ mol. (a) When ${\mathrm{Br}}_2(l)$ boils at its normal boiling point, does its entropy increase or decrease? (b) Calculate the value of $\mathrm{\Delta }S$ when $1.00\mathrm{mol}$ of ${\mathrm{Br}}_2(l)$ is vaporized at $58.8{}^{\circ }\mathrm{C}$.

The element gallium (Ga) freezes at ${29.8}^{\circ }\mathrm{C},$ and its molar enthalpy of fusion is $\mathrm{\Delta }{H}_{\text{fus }}=5.59\mathrm{kJ}/\mathrm{mol}$. (a) When molten gallium solidifies to $\mathrm{Ga}(s)$ at its normal melting point, is $\mathrm{\Delta }S$ positive or negative? (b) Calculate the value of $\mathrm{\Delta }S$ when $60.0\mathrm{g}$ of $\mathrm{Ga}(l)$ solidifies at ${29.8}^{\circ }\mathrm{C}$

(a) Express the second law of thermodynamics in words. (b) If the entropy of the system increases during a reversible process, what can you say about the entropy change of the surroundings? (c) In a certain spontaneous process the system undergoes an entropy change, $\mathrm{\Delta }S=42\mathrm{J}/\mathrm{K}.$ What can you conclude about ?