Explain the change of heat energy in a physical change.

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Solution

Physical change: The change in which no new substance is formed, and the chemical composition of the original substance is not altered.
Energy changes in a physical change:
In a physical change, A change of state and the dissolving of a substance in a liquid involves a change in energy.
A change of state from solid to liquid, or from liquid to gas, the inter-molecular force of attraction between the molecules has to be decreased so that the inter-molecular space increases.
This is possible only when the solid or the liquid absorbs some heat energy.
Changes observed during inter-conversion of states of matter:
Conversion of a solid substance into a liquid substance - Heat energy absorbed(Endothermic change)
Conversion of a liquid substance into a gaseous substance - Heat energy absorbed. (Endothermic change)
Conversion of a liquid substance into a solid substance - Heat energy released(Exothermic change)
Example: Melting of ice absorbs heat energy, and water while boiling absorbs heat energy.

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