What does a exothermic mean in scince

An exothermic reaction is one that, through either light or heat, releases energy.

It can be expressed simply as:

reactants --> products + energy

The potential energy at the end of the reaction is always lower than at the beginning of the reaction.

An endothermic reaction is a reaction that absorbs energy from its surroundings.

It is essentially reactants + energy > products.

Hope this helps,

Brian

Exothermic is the one that increases temperature and endothermic decreases temperature