Exothermic and Endothermic Reaction

Chemical reactions that absorb energy - endothermic
   - which is a reaction takes more energy to break down bonds
eg) ice packers
Chemical reactions that release energy - exothermic
  - which is a reaction takes less energy to break down bonds
eg) chemical bonds give off energy to join together.

This graph shows an endothermic reaction where the molecules absorb more energy than they release.
The products have a higher level than the reactants. Energy of Activated complex shows the peak where they absorb energy. Activated energy tells us how much energy are used in the reaction.

The above picture shows an exothermic reaction. Note that the level of reactants and products reverse. To calculate the amount of energy, simply minus reactants from products. You always get a negative number.

This video below shows how to get the change in H and how to tell by looking at it from the graph.