17.20Ideal gases A (red spheres) and B (blue spheres) occupy two separate bulbs. The contents of both bulbs constitute the initial state of an isolated system. Consider the process that occurs when the stopcock is opened. (a) Sketch the final (equilibrium) state of the system. (b) What are the signs ( , , or 0) of ∆H, ∆S, and ∆G for this process? Explain. (c) How does this process illustrate the second law of thermodynamics? (d) Is the reverse process spontaneous or nonspontaneous? Explain.

17.21What are the signs ( , , or 0) of ∆H, ∆S, and ∆G for the spontaneous sublimation of a crystalline solid? Explain.

17.22What are the signs ( , , or 0) of ∆H, ∆S, and ∆G for the spontaneous condensation of a vapor to a liquid? Explain.

17.23An ideal gas is compressed at constant temperature. What are the signs ( , , or 0) of ∆H, ∆S, and ∆G for the process? Explain.

Consider the following spontaneous reaction of A 2 molecules (red) and B 2 molecules (blue): (a) Write a balanced equation for the reaction. (b) What are the signs ( , , or 0) of ∆H, ∆S, and ∆G for the reaction? Explain

Consider the dissociation reaction A 2 (g) 2 A(g). The following pictures represent two possible initial states and the equilibrium state of the system: Is the reaction quotient Q p for initial state 1 greater than, less than, or equal to the equilibrium constant K p ? Is Q p for initial state 2 greater than, less than, or equal to K p ? What are the signs ( , , or 0) of ∆H, ∆S, and ∆G when the system goes from initial state 1 to the equilibrium state? Explain. Is this a spontaneous process? What are the signs ( , , or 0) of ∆H, ∆S, and ∆G when the system goes from initial state 2 to the equilibrium state? Explain. Is this a spontaneous process? Relate each of the pictures to the graph in Figure (a) (b) (c) (d) 17.25

17.26Consider again the dissociation reaction A 2 (g) 2 A(g) (Problem 17.25). What are the signs ( , , or 0) of the standard enthalpy change, ∆H°, and the standard entropy change, ∆S°, for the forward reaction? Distinguish between the meaning of ∆S° for the dissociation reaction and ∆S for the process in which the system goes from initial state 1 to the equilibrium state (pictured in Problem 17.25). Can you say anything about the sign of ∆G° for the dissociation reaction? How does ∆G° depend on temperature? Will ∆G° increase, decrease, or remain the same if the temperature increases? Will the equilibrium constant K p increase, decrease, or remain the same if the temperature increases? How will the picture for the equilibrium state (Problem 17.25) change if the temperature increases? What is the value of ∆G for the dissociation reaction when the system is at equilibrium? (a) (b) (c) (d) (e)

17.27Consider the following graph of the total free energy of reactants and products versus reaction progress for a general reaction, Reactants Products: Account for the shape of the curve, and identify the point at which ∆G  0. What is the significance of that point? Why is the minimum in the plot on the left side of the graph? (a) (b)

The following pictures represent equilibrium mixtures for the interconversion of A molecules (red) and X, Y, or Z molecules (blue): What is the sign of ∆G for each of the three reactions? 17.28

17.29The following pictures represent the composition of the equilibrium mixture at 25°C and 45°C for the reaction A B, where A molecules are represented by red spheres, and B molecules, by blue spheres. What are the signs of ∆H° and ∆S° for the forward reaction A B? Explain. (You may assume that ∆H° and ∆S° are independent of temperature.)