Let us learn in detail about the conditions required for a chemical change or reaction. There are 8 essential conditions. The substances or reactants need to be in close contact with each other, example grinding or dissolving of the reactants. Most of the reactants react well in the gaseous state, hence the state of the substances is also very important. Heat increases the rate of chemical reaction, hence optimum temperature needs to be maintained. The presence or absence of light is also very important. Some reactions take place only in the presence of light. They are called photochemical reactions, example photosynthesis. Some reactions occur only when electricity is passed. The amount of pressure involved is also another important condition. The presence or absence of a catalyst and promoter. The concentration of the reactants. Sometimes more the rate of concentration faster the reaction occurs.