Question

which type of reaction is always spontaneous?
an endothermic
reaction that has
a decrease in
disorder
an endothermic
reaction that has
an increase in
disorder
an exothermic
reaction that has
a decrease in
disorder
an exothermic
reaction that has
an increase in
disorder

Explanation:

Spontaneity of a reaction is determined by the Gibbs free energy change, $\Delta G = \Delta H - T\Delta S$, where $\Delta H$ is enthalpy change, $T$ is temperature, and $\Delta S$ is entropy (disorder) change. A reaction is always spontaneous when $\Delta G < 0$. For an exothermic reaction, $\Delta H < 0$; an increase in disorder means $\Delta S > 0$. Substituting these into the formula gives $\Delta G = \text{negative} - T(\text{positive})$, which will always be negative at any positive temperature, making the reaction spontaneous.

Answer:

an exothermic reaction that has an increase in disorder