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Physical And Chemical Changes

Physical And Chemical Changes
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There are different types of changes occurring in our surroundings. Examples are – rising of the sun, trees growing, burning of coal, different size and shape of the moon, etc.

Physical Properties- Size, shape and state of a particle are said to be physical properties. For example – In the case of a sheet, when it is folded its shape change.

 Chemical Properties – Chemical properties are the internal properties of a substance. For example – The internal properties of milk and curd are different though curd is formed from milk.                                                                                                                                         

  Reversible and Irreversible – When the processes or things can be reversed when they are known as reversible. When the reverse is not possible then it is called as irreversible.

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Physical Change

When there is only a change in the physical properties of a substance and thus no new particle if formed then it is called a physical change. Physical changes are generally reversible in nature.

Examples-

Folding a paper – When a paper is folded then it changes its shape and size. It can also be unfolded, hence it is reversible.

Melting of wax – When max is melted, only its state gets changed but no new substance is formed. Solid turns into a liquid which again can get into the form of solid and thus it is also reversible.

Ice melting into water – When ice is melted only the state changes from solid to liquid. Again water can be converted into ice. Hence it is also reversible.

class 7 motion

 

Chemical Changes

When the chemical properties of the substance changes also a new substance is formed then in that case the changes are called as chemical changes. Some chemical changes are irreversible.

Examples

Burning wood, paper, etc. - In case of burning something many new substances gets created especially carbon dioxide. If a substance is burnt then it cannot be turned back to its original state. Thus burning any substance is a chemical and irreversible change.

Reaction between iron and copper sulphate solution – The solution of a copper solution is of blue colour. If you leave any shaving blade or iron nail in copper sulphate solution the colour changes from blue to pale green for some time. This occurs due to the formation of iron sulphate.

Painting – Substances like grills, iron gates are painted

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Characteristics of physical changes

  • Physical change brings changes in physical properties of substances only.
  • Mostly physical changes are reversible.
  • No new substance is formed

 

 

Characteristics of chemical changes

  • It changes the internal chemical properties of substances
  • It forms a new substance
  • It cannot be easily reversed.

 

Signs of Chemical Change

  • Difference in smell
  • Gas evolution
  • Color changes
  • Heat evolves
  • Sound is produced

 

Recap

  • In our surroundings there are changes happening everywhere.

 

  • Basically, there are two types of changes –
  1. Physical changes
  2. Chemical changes

 

  • Physical change brings change in physical properties and is reversible.

 

  • Chemical changes are irreversible and change chemical properties.

 

  • Examples of physical change are melting of ice, melting of wax, folding of sheet, etc.

 

  • Examples of chemical changes are burning of wood, burning of paper, rusting of iron, etc.

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