Identify an energy diagram showing the energy of the reaction as a function of the progress of the reaction.

The energy diagram showing the energy of the reaction as a function of the progress of the reaction is a potential energy diagram.

A potential energy diagram of a chemical reaction shows the net change in energy as reactants change into products.

The net change in energy corresponds to the change in Gibb's free energy (delta G) for a reaction. This also relates to the change in enthalpy (delta H) for a reaction. The gain or loss of energy by the reaction from or to the surroundings indicates whether a reaction is endothermic or exothermic.

An endothermic reaction involves a net increase in potential energy as reactants change into products. Energy is gained by the system from the surroundings. So, delta H is positive. This type of reaction will feel cold, or absorb heat.

An exothermic reaction involves a net decrease, so dealt H is negative. This type of reaction will feel warm or give of heat.