Changes take place around us all the time. A change refers to an alteration in physical properties or an alteration in the composition of matter. When ice melts or water evaporates, only the physical state changes. When iron is exposed to moist conditions, a reddish-brown new substance called rust forms – here the composition changes. Changes are studied as physical or chemical, endothermic or exothermic, and periodic or non-periodic.
1. Physical Change and Chemical Change – A First Look
- When a cup of water is heated, it becomes hotter and at some point becomes water vapour. It remains water at all times; only its volume changes – a physical change.
- When paper is burnt, it changes to carbon dioxide and other substances, and we cannot get the paper back. As there is a change in the chemical nature, it is a chemical change.