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CNMS ICSE - 7 Std
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Key Terms

Chapter: 02. Physical And Chemical Changes

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Natural changes: Changes that occur naturally and are beyond the control of human beings.
Human-made changes: Changes that occur due to human efforts or activities.
Slow changes: Changes that take a longer time to complete.
Fast changes: Changes that take shorter time to complete.
Desirable changes: Changes that are beneficial to humankind and we want them to take place.
Undesirable changes: Changes that are harmful to humankind and we do not want them to take place.
Periodic changes: Changes that occur at fixed intervals of time.
Non-periodic changes: Changes that do not occur at fixed intervals of time.
Reversible changes: Changes that can be reversed easily by reversing the conditions to obtain a substance in its original form.
Irreversible changes: Changes that cannot be reversed even by reversing the conditions to obtain a substance in its original form.
Physical properties: The shape, size, colour and state of a substance.
Physical change: A change in which only the physical properties of a substance change and no new substance is formed.
Melting: The process during which a solid changes into its liquid state at a fixed temperature on heating.
Freezing: The process during which a liquid changes into its solid state at a fixed temperature on cooling.
Boiling: The process during which a liquid changes into its gaseous state at a fixed temperature on heating.
Condensation: The process during which a gas changes into its liquid state at a fixed temperature on cooling.
Evaporation: The process during which a liquid changes into its vapour at a temperature below its boiling point.
Sublimation: The process of change of a solid directly into a gas on heating.
Deposition: The process of change of a gas directly into a solid on cooling.
Chemical change: A change in which the chemical composition and properties of a substance change and one or more new substances are formed.
Endothermic change: A change in which heat energy is absorbed.
Exothermic change: A change in which heat energy is evolved (released).
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