Physical and Chemical Changes

Physical and Chemical Changes

We see ice melting into water, water boiling to vapours and vapours precipitating into the water droplets on cooling. These are some of the examples of Physical Changes since the transition is in the Physical Properties of Water. Substances in Nature undergo various types of changes. The changes that they can undergo are widely classified into two categories viz. Physical and Chemical Changes.

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Physical Changes

Chemical Changes

Changes in the Physical Properties of a Substance are known as Physical Changes. Physical Properties of a Substance include colour, size, shape, state, temperature, odour, appearance, texture and many more. In addition, Physical Changes do not lead to the formation of new substances. Physical Changes may or may not be reversible.

Examples of Physical Change

  • Breaking/Crushing of any Object
  • Expansion of Metal on Heating
  • Dissolving Sugar or Salt (Solute) in Water (Solvent) (as a result, a solution is formed)
  • Solidification of Molten Metal on Cooling
  • Shredding Paper

Chemical Changes

One or more substances, at times, react with one another or substances which are readily available in the environment. This consequently leads to the formation of a new substance(s). The formation of the new substance can also be accompanied by one or more of the following:

  • Emission of Heat (Exothermic Reaction) as a result of a Chemical Changes
  • Absorption of Heat (Endothermic Reaction) as a result of a Chemical Changes
  • Emission Light as a result of a Chemical Changes
  • Production of Sound as a result of a Chemical Changes
  • Change or emission of Odour as a result of a Chemical Changes
  • Emission of Gas as a result of a Chemical Changes
  • and so on.

Examples of Chemical Change

Learn more about the Chemistry of Rusting of Iron here.

Solved Examples for You

Question: Which among the following is not a physical change?

  1. Melting of solids to liquids
  2. Vaporisation of liquids to gasses
  3. Liquification of gasses to liquids
  4. Decay of matter

Solution: D. The decay of matter is nuclear phenomenon so this is not a physical change, apart from this all other changes are physical changes.

Question: Which of the following represents effect/(s) of a chemical change?

  1. Heat, light or any other radiation (ultraviolet, for example) may be given off or absorbed.
  2. A sound may be produced.
  3. A change in smell may take place or a new smell may be given off.
  4. All of the above.

Solution: D. The following represents effect/(s) of a chemical change. Heat, light or any other radiation (ultraviolet, for example) may be given off or absorbed. A sound may be produced. A change in smell may take place or a new smell may be given off. A colour change may take place. A gas may be formed.

Question: Which of the following are physical changes?
(i) Melting of iron metal
(ii) Rusting of iron
(iii) Bending of an iron rod
(iv) Drawing a wire of iron metal

  1. (i), (ii) and (iii)
  2. (ii), (iii) and (iv)
  3. (i), (iii) and (iv)
  4. (i), (ii) and (iv)

Solution: C

Chemical Change

Rusting of iron is a redox reaction and its a chemical change, apart from this all others are physical changes.The rusting of Iron (Iron in contact with water forms the anode and in contact with air forms the cathode. At the anode, iron is oxidised to Fe2+ and at the cathode, oxygen is reduced to water.
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