PHYSICAL AND CHEMICAL CHANGES FOR NDA 2022 | CHEMISTRY FOR NDA | HELP4NDA

There are some changes during which no new substances are formed whereas during some other changes new substances are formed. Therefore on this basis we can classify all the changes into two groups- physical changes and chemical changes 

1. Physical Changes

A physical change is a change in which the composition of a substance is not affected, i.e. no new substance is formed. e.g. Interconversion of states is a physical change because these changes occur without a change in composition and no change in the chemical nature of the substance. When an ordinary piece of iron is magnetised in the presence of a strong magnetic field. Here the colour, density, mass and the composition remains the same. Hence, magnetisation is a physical change. The physical changes are reversible. Magnetisation can be reversed by heating the piece of iron.

Evaporation, distillation, sublimation, condensation and crystallisation are examples of physical changes. The blue colour of copper sulphate crystal disappears when it is heated strongly because on heating water of crystallisation of crystal is lost. It regains its blue colour when moistened with a drop of water.

CuSO4.5H2O → CuSO4+5H2O

   blue                                     white

It is an example of a physical change .

# Some facts about the physical changes are
(i) Physical changes are temporary and reversible.
(ii) Composition of the constituent of matter remains same during physical change i.e. constituent particles of matter does not change.
(iii) Physical changes are due to the change in physical properties like density, volume, state temporarily.

Note

• Amount of space that a substance or object occupies is called volume of that substance.
• Density is the degree of compactness of a substance. It is defined as mass per unit volume.
i.e. Density=Mass/Volume

MORE EXAMPLES OF PHYSICAL CHANGES :

• ice to water 
• vaporization of water and their reverse process 
• candle melting 
• melting of anything 
• Sublimation of camphor (as camphor directly converts to gas and can be converted back to camphor) 
• boiling water 
• dry cut wood 
• chopping vegetables with a knife 
•  transpiration in plants

2. Chemical Changes

These changes result in the formation of new substances. In a chemical change, the composition and molecular structure of the substance undergoing changes are considered.
e.g. When a piece of iron or nail is left in moist air for a long time, it rusts and gives a reddish brown look. During rusting process iron combines with oxygen to give a new product.
Here rusting, is a chemical change which cannot be reversed back by any physical process. As we eat food, the digestion of food starts from the mouth and during this process many chemical changes take place in the stomach.

The complex food material gets converted into simple molecules of glucose which is oxidised in the body cells to release energy
Similarly, burning of any substance is a chemical change. Burning is always accompanied by the production of heat. Explosion of a fire work is also a chemical change (heat, light, sound and unpleasant gases are produced in
explosion).
Blue copper sulphate crystals on heating loses its all water molecules giving white anhydrous salt which decomposes into black cupric oxide and sulphur trioxide on strong heating .

Note

• Burning of a candle is an example of both physical and chemical changes.
• Ozone is decomposed to oxygen in the presence of ultraviolet rays. It is an example of chemical change.
Some facts about the chemical changes are
(i) During chemical changes, the composition of the substance changes due to change in constituent particles of substance.
(ii) Identity of the substance is lost during a chemical change.
(iii) Energy is absorbed or released during a chemical change.
(iv) Chemical change is permanent and irreversible.

MORE EXAMPLES OF CHEMICAL CHANGES : 

•  Ripening of fruits
•  Ripening of food 
•  Respiration 
•  Photosynthesis
•  Rusting of iron 
•  Copper turning green 
•  Corrosion of metals
•  Oxidation reduction and all chemical reactions (except a few reversible  reactions) 
• Leaf cleavage from tree to yellow 
• Drying of leaves

Previous Years' Questions

Directions (Q. Nos. 1-2) Following questions consist of two statements, I and II. Examine these two statements and select the correct choice according to the codes given below.

(a) Both the statements are true and Statement Il is the correct

explanation of Statement I

(b) Both the statements are true but Statement ll is not the correct

explanation of Statement I.

(c) Statement is true, but Statement II is false.

(d) Statement is false, but Statement II is true.

 1. Statement I Conversion of blue copper sulphate to black cupric

oxide on heating is a physical change.

Statement II A change in which chemical composition does not

change is called physical change.

2. Statement I The bule colour of copper sulphate crystal disappears

when it is heated strongly.

Statement II Due to heating water of crystallisation of crystal is lost.

2012 (1)

 

3. Which one among the following is not a chemical change? 2013 (1)

(a) Curdling of milk 

(b) Ripening of fruits

(c) Evaporation of water

(d) Burning of coal

 

4. A sample of carbon dioxide that undergoes a transformation from

solid to liquid and then to gas would undergo

2014 (II)

(a) a change in mass

(b) a change in density

(c) a change in composition

(d) no change in physical properties

 

5. Which one of the following is not a chemical change?

2016 (1)

(a) Ripening of fruits

(b) Curdling of milk

(c) Freezing of water

(d) Digestion of food

NDA MATHEMATICS NOTES :

#COMPLEX NO.

#SET THEORY

#RELATION 

#PERMUTATION AND COMBINATION

#PROBABILITY

#VECTOR

#LOGARITHM

#BINARY NO.

PREVIOUS YEAR QUESTIONS OF CHEMISTRY

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