Chapter 19

Consider a reaction ${\mathrm{A}}_2(g)+{\mathrm{B}}_2(g)\rightleftharpoons 2\mathrm{AB}(g)$, with atoms of A shown in red and atoms of B shown in blue. (a) If $K_c=1$, which system is at equilibrium? (b) What is the sign of $\mathrm{\Delta }G$ for any process in which the contents of a reaction vessel move to equilibrium? (c) Rank the boxes in order of increasing magnitude of $\mathrm{\Delta }G$ for the reaction. [Sections $19.5$ and $19.7]$

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 ${\mathrm{N}}_2$ molecules at ${25}^{\circ }\mathrm{C}$ and $1\mathrm{atm}$, (d) lightning, (e) formation of ${\mathrm{CH}}_4$ and ${\mathrm{O}}_2$ molecules from ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$ at room temperature and 1 atm of pressure?

Which of the following processes are spontaneous: (a) the melting of ice cubes at ${10}^{\circ }\mathrm{C}$ and 1 atm pressure; (b) separating a mixture of ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ into two separate samples, one that is pure ${\mathrm{N}}_2$ and one that is pure ${\mathrm{O}}_2$; (c) alignment of iron filings in a magnetic field; (d) the reaction of sodium metal with chlorine gas to form sodium chloride; (e) the dissolution of $\mathrm{HCl}(g)$ in water to form concentrated hydrochloric acid?

(a) Give two examples of endothermic processes that are spontaneous. (b) Give an example of a process that is spontaneous at one temperature but nonspontaneous at a different temperature.

The crystalline hydrate $\mathrm{Cd}{\left({\mathrm{NO}}_3\right)}_2\cdot 4{\mathrm{H}}_2\mathrm{O}(s)$ loses water when placed in a large, closed, dry vessel: $\mathrm{Cd}{\left({\mathrm{NO}}_3\right)}_2\cdot 4{\mathrm{H}}_2\mathrm{O}(s)⟶\mathrm{Cd}{\left({\mathrm{NO}}_3\right)}_2(s)+4{\mathrm{H}}_2\mathrm{O}(g)$ This process occurs even though it is endothermic; that is, $\mathrm{\Delta }H$ is positive. Is this process an exception to Bertholet's generalization? Explain.

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?

The normal freezing point of 1 -propanol $\left({\mathrm{C}}_3{\mathrm{H}}_3\mathrm{O}\right)$ is $-127{}^{\circ }\mathrm{C}$. (a) Is the freezing of 1 -propanol an endothermic or exothermic process? (b) In what temperature range is the freezing of 1 -propanol a spontaneous process? (c) In what temperature range is it a nonspontaneous process? (d) Is there any temperature at which liquid and solid 1-propanol are in equilibrium? Explain.

(a) What is special about a reversible process? (b) Suppose a reversible process is reversed, restoring the system to its original state. What can be said about the surroundings after the process is reversed? (c) Under what circumstances will the vaporization of water to steam be a reversible process? (d) Are any of the processes that occur in the world around us reversible in nature? Explain.

(a) What is meant by calling a process irreversible? (b) After an 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.