Question

The entropy of combustion of benzoic acid is zero. This means that...

a)combustion is not spontaneous here.
b)combustion is spontaneous, however, since the reaction is exothermic.
c)combustion is spontaneous, however, since the reaction is endothermic.
d)combustion is nonspontaneous even though the reaction is exothermic.

I think a) combustion is not spontaneous here.
... but I'm really not sure at all

Answer 1

When we burn benzoic acid (for example in a calorimeter to calibrate the calorimeter), the calorimeter temperature rises; therefore, heat must be given off. That means the reaction is exothermic if I'm not on the wrong track here. And that means a isn't right. If delta S = 0, then Tdelta S = 0 and delta G = delta H. If delta H is exothermic, that makes delta H negative and that makes delta G negative. I would go with answer B. One may ask why benzoic is stable at room temperature instead of spontaneously combusting; I would answer that the activation energy had to be overcome to get the reaction started.