- One or more new substances are formed as a result of a chemical change. When we burn a piece of paper with a lit match stick, we produce entirely new substances such as carbon dioxide, water vapour, smoke, and ash.
- A chemical change is usually irreversible: For example, burning paper is a permanent and irreversible change. This is due to the fact that we cannot recombine the byproducts of paper burning to produce the original paper.
- During a chemical change, a large amount of energy (in the form of heat, light, and sound) is either absorbed or released: A chemical change occurs when a cracker is burned. When a cracker explodes, it emits heat, light, and sound energy.
- A chemical change may result in a smell change or the release of a new smell: When food spoils, it emits an unpleasant odour. This indicates that new substances have formed in spoiled food, which has a foul odour.
- A chemical change could cause a permanent colour change: Fruit ripening is a chemical transformation. As raw fruit ripens, its colour changes.
- A chemical reaction can result in the formation of a gas. For example, when a metal, like zinc, reacts with diluted hydrochloric acid, zinc chloride salt and hydrogen gas are produced.
- Some of the examples of chemical changes are:
- Plants combine carbon dioxide and water in the presence of chlorophyll and sunlight to form two new substances, glucose and oxygen gas, during photosynthesis. Thus, photosynthesis is a chemical change.
- During digestion, various food materials break down to form new substances that can be absorbed by the body. Thus, digestion is a chemical change.
