Physical and chemical changes are associated with energy changes.
For this we have to understand the type of changes.
1. Exothermic :- These are the changes that release energy when they occur .
2. Endothermic :- The changes that occur by absorbing the energy are the endothermic .
In case of chemical change the reaction proceeds by crossing an energy barrier.
for the conversion of reactant into products there is a minimum required energy that is called threshold energy. If the reactant do not have threshold energy , the reaction will not take place.