Changes in energy are always accompanied by some kind of change (chemically or physically). During the reaction, the old bonds in the reactants break and the new bonds in the products are formed.
During this breaking and making of bonds, there is a difference in energy. If the energy required to break the bonds is greater than the energy required to make the bonds, then the energy is given out to the surroundings.
Such reactions or changes are exothermic. But if the energy required to break the bonds is less than the energy required to make the bonds, then the energy is absorbed from the surroundings. Such reactions are said to be endothermic reactions.
A change during which the molecular composition gets totally altered, that is change in which a new product is always formed is called a chemical change.
Is burning wood a chemical change?
A burning of wood is a chemical change results in the formation of a new product. An entirely new product is formed with a complete difference in molecular composition. The change is permanent and irreversible. It means that the chemical change cannot be reversed by altering or changing the experimental conditions.
The mass of the substance gets altered during a chemical change. During a chemical change either the mass is added or removed. It results in either an increase in weight or a decrease in the weight of the substance.
Characteristics of Chemical Change
Energy changes take place during a chemical change. There is a difference in energy in the breaking of old bonds in reactants and the formation of new bonds in products. Energy is either absorbed or released during the chemical change.
If the energy is released then the reaction is known as an exothermic reaction and if the energy is absorbed then the reaction is known as an endothermic reaction.
Another example – when a paper is burnt, it forms carbon dioxide and water vapor along with energy in the form of heat and light.
More Example Chemical Change has given Below:-
- Burning of candle
- Souring of milk
- Burning of camphor
- Burning of wood or paper
- Rancidification of butter
- Digestion of food
- Rusting of iron
- Combustion of fuel
- Electrolysis of water
On the other hand, many changes occur in our natural environment like the evaporation of water, condensation of water vapors, rainfall etc. In these changes, only the change in state is involved.
Such changes are referred to as physical changes.The physical change may be defined as the change which occurs in size, shape, color, texture, state, magnetic or electrical condition but the molecular composition remains totally unaltered, ie., no new product is formed as a result of physical change.
Characteristic of the Physical Change
- No new product is formed. The molecular composition remains totally unaltered. During the physical change only the arrangement of molecules gets altered leading to the change in state. For example, the molecular compositions of ice and water remain same.
- The change is temporary and reversible. If the cause producing the change is removed, then the reaction gets reversed. For example, ice on melting forms water and water on freezing produces ice.
- No energy changes take place as a result of physical change. The energy required to bring about a physical change is generally equal to the amount of energy required to reverse the change. Therefore there is no change in energy.
- The mass of the substance remains same during a physical change. There is no involvement of mass during physical change but only energy is added or removed. No matter is added or removed during a physical change and hence the mass of the substance remains the same.
More Below are the Examples of Physical Change:-
- Melting of wax
- Boiling of water
- Freezing of water
- Melting of ice
- Dissolution of sugar in water
- Cutting of wood
- Heating of zinc oxide
- Heating of camphor
- Heating of ammonium chloride
- Dissolution of sulfur in carbon disulphide
Physical Change Vs Chemical Change:-
|S.No||Physical change||Chemical change|
|1||A change which alters only the physical properties but the molecular composition remains totally unaltered.||A change which alters all the physical properties and the molecular composition is called chemical change.|
|2||No new results are formed as a result of physical change.||A new substance is always formed as a result of chemical change.|
|3||The change is temporary.||The change is permanent.|
|4||The change is reversible.||The change is irreversible.|
|5||No energy change takes place as a result of physical change.||Energy changes takes place as a result of chemical change.|
|6||Mass of a substance undergoing physical change remains totally unaltered.||Mass of a substance gets totally altered during a chemical change.|
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