Concise Selina Solutions for Class 9 Chemistry Chapter 2 Chemical Changes and Reaction

Chemical Changes are also called Chemical Reactions. Chemical reactions involve combining different substances. The chemical reaction produces a new substance with new and different physical and chemical properties. The matter is never destroyed or created in chemical reactions. Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create other substances as products. A chemical reaction is a permanent change in which the process of chemical bond breakage takes place along with the formation of new bonds. A chemical change occurs when particles collide with each other when they are in close contact or else with the help of energy.

A reaction in which heat is given out is called exothermic reactions; in exothermic reactions, energy is released.

A reaction in which heat is absorbed is called an endothermic reaction. In endothermic reactions, energy is utilized.