Physical Changes
Changes in which no new substance is formed are called physical changes. In physical change, the chemical composition and molecular structure of the substance do not change. Following are the characteristics of physical change:(1) In physical changes, new substances are not formed (basic characteristic).
(2) The characteristic properties of the original substance do not change in physical changes, that is, the chemical nature of the substance does not change (basic properties).
(3) Physical changes are usually temporary. The process lasts only as long as the cause of the process lasts. When the cause of the process is removed, the process reverses (secondary symptom).
Changes in the physical state, condition, shape, size, volume etc. of substances are physical changes. Processes like melting, evaporation, condensation, freezing etc. of substances and processes like distillation, sublimation etc. are physical changes.
Chemical Changes
Changes in which new substances are formed are called chemical changes. In a chemical change, the chemical composition of the original substance and its molecular structure or only the molecular structure changes. The following are the characteristics of a chemical change:
(1) The properties of matter change in chemical changes, that is, the chemical nature of matter changes (basic character).
(2) In a chemical change, new substances are formed, whose properties are different from those of the original substance.(basic symptom).
(3) Chemical changes are usually permanent. Procedure on removal of reason for changeDoes not reverse (secondary symptom).
(4) Energy changes in chemical changes are more than in physical changes. In these changes, heat, light, etc., are often released or absorbed (secondary symptoms).
Burning of substances, rusting, fermentation, combination reactions, decomposition reactions, allotropic changes, isomeric changes and all other chemical reactions are chemical changes.
Nuclear Change.
Such changes in which the composition of the atomic nucleus changes and new types of atoms are formed from one type of atoms are called nuclear changes. For example,
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