Chemical reactions that absorb energy are called endothermic. Chemical reactions that absorb free energy are called endothermic reactions. Chemical reactions that release free energy are called exothermic reactions.
Heat energy is necessary for some chemical reactions to occur. Some chemical reactions are endothermic meaning they require or absorb energy for a chemical reaction to occur. Other chemical reaction are exothermic meaning they release energy when the chemical reaction takes place..
The light dependent reactions take in the light energy and convert that to chemical energy, but it is in the Calvin cycle (light independent reactions) where the chemical energy is stored in a complex sugar.