# How do you tell the difference between an endothermic reaction and an exothermic reaction?

Feb 20, 2017

Are you referring to the equations of these reactions? If so, read on...

#### Explanation:

When we write the equation of an exothermic reaction, we either include the energy released on the product side of the equation, or better still, we write $\Delta H$ for the reaction and state the value of the heat of reaction. This will be a negative number for an exothermic reaction.

Example:

${C}_{6} {H}_{12} {O}_{6} + 6 {O}_{2} \rightarrow 6 C {O}_{2} + 6 {H}_{2} O$ $\Delta H = - 2802 \frac{k J}{\text{mol}}$

In an endothermic reaction, the energy term can be written as part of the reactants, or using the same $\Delta H$ notation, the value will be positive.

In a practical sense, telling these apart is easy, as the exothermic reaction will generate heat (although sometimes in small amounts, or too slowly to be easily noticeable). An endothermic reaction will generally be accompanied by a cooling of the reaction vessel.