Most of the energy produced in modern society comes from chemical reactions. Our study of nature has resulted in Three Laws of Thermodynamics . We studied the first law last semester. The total quantity of energy in the universe is assumed to be a constant.
Energy is converted from one form to another while the total remains the same.
We studied Hess's Law and H in conjunction with the first law. A spontaneous process is a physical or chemical change that occurs by itself . It can start by itself, or once started it continues by itself without further exertion. Remember rate or speed of reaction is the concern of kinetics. It could be a fraction of a second or 100 years before a measurable amount of products is formed.