Exothermic reactions are reactions that release energy. An example of exothermic reactions is combustion or burning. Endothermic reactions on the other hand absorb energy. An example of an endothermic reaction is melting of ice.
For exothermic reactions, since the heat is released, we see heat on the product side of the equation. Also, change in enthalpy will have a negative sign.
For endothermic reactions, since the heat is absorbed, we see heat on the reactant side of the equation. Also, change in enthalpy will have a positive sign.
An exothermic reaction is not necessarily spontaneous, there is another factor that needs to be taken into account, entropy.
We will discuss entropy in the next article.