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Physical change is a temporary or reversible change in which no new substances are formed. Examples:
Characteristics of physical changes
A chemical change is a permanent and usually irreversible change in which new substances with different properties are formed.
Characteristics of chemical change
|Physical change||Chemical change|
|No new substances are formed.||New substances are formed.|
|It is a temporary change in which chemical composition of the substance remains the same.||It is a permanent change in which chemical composition of the substance changed.|
|Change in energy is not usually seen in it.||Change in energy is visible.|
|Change in mass is not seen. E.g., dissolving the salt in water||Change in mass is seen in it, e.g., rusting of iron.|
|Only the physical properties like colour, taste or state are changed.||Chemical, as well as physical properties, are changed.|
|It is usually reversible.||It is usually irreversible.|
The process by which a chemical change takes place is called as a chemical reaction. Those substances that take part in a chemical reaction are called reactants. Those substances which are formed by a chemical reaction are called products.
The chemical reaction which is expressed in terms of full names of reactant and product molecules is called word equation. For example, Hydrogen reacts with oxygen to produce water.
Hydrogen + oxygen→Water
The chemical reaction which is expressed by using themolecular formula of reactants and products is called chemical equation. The chemical equation is also called formula equation.
2 H2 + O2→2 H2O
A physical change is a temporary change in which only the physical state or appearance of the substance changes and no new substances are formed.
For example: Melting of ice, evaporation of water etc.
A chemical change is a permanent change in which new substances with different properties are formed.
For example: Electrolysis of water, burning of kerosene etc.
The differences between physical and chemical change are as follows:
|Physical Change||Chemical Change|
|In a physical change only physical properties are changed.||In a chemical change, the chemical composition and chemical properties are changed.|
|No new substances are formed||New substances are formed.|
|It is generally a temporary change.||It is a permanent change.|
The main factors that bring out a chemical change are:
Heat supplied gives energy to the molecules of the reactants and makes them collide to each other to bring about chemical reaction. Examples are:
CaCO3 Heat → CaO + CO2
2KClO3 Heat → 2KCl +3O2
Electricity brings both synthesis and decomposition reaction. For example:
2H2O Electrolysis→ 2H2 + O2
2H2 + O2 Electrolysis→ 2H2O
Some of the chemical reaction takes place in the present of light. For example:
2AgBr Sunlight→ 2Ag + Br2
CH4 + Cl2 Uv-rays → CH3Cl + HCl