lecture 1 Chemical equilibrium; introduction, reaction and it's types

Chemical reactions are the processes by which chemicals interact to form new chemicals with different compositions. Simply stated, a chemical reaction is the process where reactants are transformed into products.
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 different substances as products.
process that can be reversed is called reversible process. A process that cannot be changed is called an irreversible process. A reversible process is temporary. An irreversible process is permanent.
In an irreversible reaction, the energy released or absorbed is typically larger than in a reversible reaction since all the reactants are consumed to form products. In a reversible reaction, the energy released or absorbed is smaller since the reaction can proceed in both directions.