Question

How to tell if a reaction is exothermic.

Answer 1

Answer:

If the reaction loses heat it is exothermic.

Answer 2

If the enthalpy change listed for a reaction is negative, then that reaction releases heat as it proceeds — the reaction is exothermic (exo- = out). If the enthalpy change listed for the reaction is positive, then that reaction absorbs heat as it proceeds — the reaction is endothermic (endo- = in).