difference between physical and chemical change
Physical and Chemical Changes. There are several differences between a physical and chemical change in matter or substances. A physical change in a substance doesn't change what the substance is. In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed. For example, if a piece of paper is cut up into small pieces it still is paper. This would be a physical change in the shape and size of the paper.
There are two possible definitions for Physical and Chemical changes which I use in school: 1. A physical change is reversible, a chemical change is not. For example, the freezing of water would be a physical change because it can be reversed, whereas the burning of wood is a chemical change - you can't 'unburn' it. 2. A physical change is a change in which no new substance is formed; a chemical change results in the formation of one or more new substances. Again, consider the previous examples: Freezing water into ice just results in water molecules which are 'stuck' together - it's still H2O.
A Chemical change may also cause a physical change; a physical change alone cannot lead to a chemical change. 3. A Physical change is superficial and can possibly be reversed; a chemical change is complete and permanent.
Physical changes can be reversed, chemical changes cannot be reversed with the substance changed back without extraordinary means, if at all. For example, a cup of water can be frozen when cooled and then can be returned to a liquid form when heated.