Final answer:
Energy required to initiate a chemical reaction is called activation energy, which typically comes from heat in the surroundings and helps reactants reach the transition state for the reaction to proceed.
Step-by-step explanation:
Any energy released in the reaction or absorbed in order to initiate the reaction comes from an external environment called the surroundings. The energy required by reactants to initiate a chemical reaction is known as activation energy.
This energy is typically sourced from heat energy in the surroundings, which accelerates the motion of molecules, thus increasing the frequency and force of their collisions and assisting them in reaching the transition state.
As a reaction proceeds, it may release energy (exothermic reaction) or require the absorption of energy (endothermic reaction).