Chemical substances that speed up the rate of a chemical reaction are called catalysts. Catalysts are substances that increase the rate of a chemical reaction by providing an alternative pathway with a lower activation energy for the reaction to occur. They do not get consumed or permanently changed in the reaction and can be reused.

Catalysts work by providing an alternative reaction mechanism that has a lower activation energy. Activation energy is the energy required for a chemical reaction to occur. By lowering the activation energy, catalysts facilitate the formation of the transition state, which is the high-energy intermediate state between the reactants and the products.

There are two types of catalysts: homogeneous catalysts and heterogeneous catalysts.

Homogeneous catalysts are in the same phase as the reactants and products. They are usually soluble in the reaction mixture. Homogeneous catalysts often form complexes with reactants, which then undergo a reaction to form products. Examples of homogeneous catalysts include acids, bases, and enzymes.

Heterogeneous catalysts are in a different phase than the reactants and products. They are usually solids while the reactants and products are gases or liquids. Heterogeneous catalysts work by adsorption, where reactant molecules are adsorbed onto the catalyst surface and react to form products. Examples of heterogeneous catalysts include metal catalysts like platinum, palladium, and nickel.

Catalysts are widely used in various industries and chemical processes to increase the rate of reactions and improve efficiency. They play a crucial role in the production of fuels, chemicals, and pharmaceuticals. They can also be used to selectively promote certain reactions and inhibit others.

In conclusion, a chemical substance that speeds up the rate of a chemical reaction is called a catalyst. Catalysts work by providing an alternative pathway with a lower activation energy for the reaction to occur. They are not consumed in the reaction and can be reused. Catalysts are essential in many industries and chemical processes to increase reaction rates and improve efficiency.