The energy level decreases in an exothermic reaction, as energy is given out to the surroundings.
The energy level increases in an endothermic reaction, as energy is taken from the surroundings.
A reaction profile is similar to an energy level diagram, but it includes the activation energy – the minimum energy that particles need when they collide for a reaction to occur. The activation energy is a hump in the line, which:
The overall change in energy is the difference between the energy of the reactants and products.