THE DIFFERENCE BETWEEN EXOTHERMIC AND ENDOTHERMIC CHEMICAL REACTIONS

All chemical reactions start with the reactants having some sort of energy activation that results in the bonding of the two material's molecules and forms a new product.
The most common form of energy is heat; either the chemical reaction will cause the product to give off heat, or absorb it.
The easiest way to start to understand the differences between endothermic and exothermic reactions can be derived from their names. "Endo" means "to draw into," and "Exo" means "to give off."

* Endothermic reactions draw heat in from their surroundings.
* Exothermic reactions give heat off to their surroundings.
* In a chemical equation, "energy" appears on the left side in an endothermic reaction and on the right side in an exothermic reaction

ENDOTHERMIC PROPERTIES EXPLAINED

* Energy is drawn in from the external environment, causing its surroundings to loose heat, or "cool down."
* The endothermic chemical reaction creates a product that has a higher energy level than the original materials, causing the reactant's stored energy to decrease. (In scientific terms, the reactants have "less total enthalpy" than the product.)
* The resulting product of the reaction is less stable because, the higher the energy bond, the less strength its molecules possess.
* Most endothermic reactions are not spontaneous.

EXOTHERMIC PROPERTIES EXPLAINED

* Exothermic chemical reactions cause their surroundings to warm up by giving off heat.
* The reactants contain more stored energy than the product because energy from external sources is not required, but given off. This gives the product more stability due to the lower amount of energy needed. (In this case, the reactants have a "greater total enthalpy" than the product.)
* Exothermic reactions are usually spontaneous.

SIMPLE EXAMPLES OF ENDOTHERMIC AND EXOTHERMIC CHEMICAL REACTIONS

Chemical reactions are all about energy and randomness. Some reactions occur as the result of entropy, which is a facet of random, spontaneous bonding, but even if a spontaneous reaction between chemicals would not normally occur, one can be created, if enough energy is applied.