Re: Can there be an exothermic reaction which releases no heat?

The term "exo-thermic" means to give out heat, so to answer your question; no, there is no exothermic reaction which doesn't release heat.

However, light can be emitted by some reactions. The heating of the rock Bleu Jaune [French for "Blue-Yellow", but often referred to in English as "Blue John Stone"] gives out light rather than heat, an example of thermoluminescence. Other kinds of photochemical reactions also release light.

Moderator's Note:
Consider also, particularly in biological systems, that exothermic reactions in a cell may provide energy to drive otherwise unfavorable endothermic reactions, producing a limited or no gain in energy release (i.e. "no heat"). However, these reactions by themselves are still exothermic in nature.