In this post, we will discuss about physical and chemical changes and their characteristics.
What is a Physical change?
A physical change may be defined as follows:
A change in which only the physical properties of the substance get changed, while its chemical composition remain unchanged, is called a physical change.
During a physical change, physical properties such as colour, volume, size, shape, magnetic properties, etc., of the substances may change.
For example, when sugar is added to water it disappears to form its solution. In solution, both water and sugar retain their properties. Sugar can be recovered from its solution by evaporating water.
Some examples of physical changes are:
- Evaporation or condensation of water or any other liquid
- Dissolution of common salt or sugar in water
- Crystallisation of a substance from its solution.
- Magnetisation of an iron piece and demagnetisation of a magnet.
What are the characteristics of a physical change?
A physical change is characterised by the following properties:
- In a physical change, only the physical properties of the substances undergo change. The chemical properties of the substances remain unchanged.
- In a physical change, no new substance is formed.
- A physical change can be reversed easily, i.e., the original form of the substance can be obtained easily by simple methods.
- Physical changes are temporary and can be reversed, i.e., physical changes are reversible.
What is chemical change?
A chemical change may be defined as follows:
A change in which chemical composition and chemical properties of the reacting substances undergo a change is called a chemical change.
Thus, due to chemical change the nature of the reacting substance is completely changed, and a new substance is formed. The new substance so formed is called the product. The properties of the product are different from those of the original reactants. For example, when carbon is burnt, carbon dioxide is produced. Carbon dioxide has properties entirely different from those of carbon.
Hence, the burning of carbon or coal is a chemical change.
Some common chemical changes are:
- Burning of coal, wood, paper, etc.
- Burning of a candle
- Souring or curdling of milk
- Burning of a matchstick
- Burning of magnesium in air
- Ripening of fruits, and growing of a plant into a tree.
- Digestion of food.
- Rusting of iron.
- Bursting of a cracker
What are the characteristics of a chemical change?
A chemical change is characterised by the following properties:
- In a chemical change, the chemical composition and chemical properties of the reacting substances are completely changed. For example, during the burning of coal, dark coloured solid gets converted into gaseous substance called carbon dioxide. The composition and properties of carbon dioxide are entirely different from those of coal.
- Whenever a chemical change take place, one or more new substances are formed. For example, during the burning of coal, the new product formed is carbon dioxide.
- A chemical change cannot be reversed easily, i.e., a substance undergoing chemical change cannot be regained by simple methods. For example, it is not possible to get back milk after it is converted into curd.
- A chemical change is a permanent change. For example, a grown tree cannot be converted back into a small plant.
- During a chemical change, a certain amount of energy in the form of heat, light or sound energy is either absorbed or evolved. For example, when a cracker burst heat, light and sound energies are evolved.
How does a physical change differ from a chemical change?
Points of difference between a physical change and chemical change are:
| Physical Change | Chemical Change |
|---|---|
| In a physical change, only physical properties such as colour, physical state, volume, etc., change. Chemical properties remain unchanged. | In a chemical change, the chemical composition and chemical properties of the reactants undergo change. |
| No new substance is formed. | One or more new substances found in a chemical change. The new substances formed have different properties from those of the reacting substances. |
| No energy in the form of heat, light or sound energy is absorbed or released. | A chemical change is always accompanied by the absorption or evolution of energy in the form of heat, light or sound energy. |
| The original form of the substance can be obtained easily by simple physical methods. | The original substance cannot be obtained by simple physical methods. |
| Physical change is generally temporary, as it can be easily reversed by reversing the conditions. | Chemical change is a permanent change, as it can’t be reversed by just reversing the conditions. |
Read more: Types of Substances: Elements and Compounds
Follow here: Telegram