Physical and Chemical Changes
Physical change is one which is easily reversible and in which no new substance is formed, for example when a solid (ice) is heated, it melts to form a liquid (water), and on cooling, the Liquid solidifies to ice again.
Other examples of Physical change;
1. Dissolution of common salt in water.
2. Melting of ice, candle wax, etc.
3. Freezing of liquid to solid.
4. Vaporisation of liquid e.g. water.
5. Liquefaction of gasses.
6. Sublimation of camphor, and iodine.
7. Magnetisation of iron.
Chemical change is one which is not easily reversible and in which new substances are formed. For example, the burning of firewood. It changes to charcoal and ash. This is a chemical change as we cannot get back the firewood anymore.
Other examples of chemical change:
1. Rusting of iron
2. Burning of any substance in air. e.g. coal, paper, magnesium ribbon, wood, etc.
3. Dissolution of metal or limestone in acid
4. Electrolysis of a compound e.g. dilute H2SO4
5. Fermentation and decay of substances e.g Alcohol, Yoghurts
6. Slaking of lime i.e adding water to quicklime
7. Changes in an electrochemical cell.
Differences between Physical and Chemical Changes:
|Physical Change:||Chemical Change:|
|1.||Easily reversible||Not easily reversible|
|2.||No new substances are formed||New substances are formed|
|3.||No change in mass||There is a noticeable change in mass|
|4.||Not accompanied by a great heat change||Usually accompanied by great heat change|