Chapter 19 - Spontaenous Change: Entropy and Gibbs Energy - Example 19-4 - Using Enthalpy and Entopy Changes to Predict the Direction of Spontaneous Change - Page 835: Practice Example A

(a) spontaneous at low temperatures and non-spontaneous at high temperatures. (b) non-spontaneous at all temperatures.

(a) Since the number of moles of gas decreases, the change in entropy $\Delta S$ is negative. With $\Delta H\lt0$ and $\Delta S\lt0$, this reaction should be spontaneous at low temperatures and non-spontaneous at high temperatures. (b) Since the number of moles of gas decreases, the change in entropy $\Delta S$ is negative. With $\Delta H\gt0$ and $\Delta S\lt0$, this reaction should be non-spontaneous at all temperatures.