CHARLES LAW

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CHARLES LAW

INTRODUCTION:

This law was presented by Charles in 1746-1823 in which he explained the relation between volume of a gas and temperature.

STATEMENT:

According to Charles Law “For a given mass of a gas its volume is directly proportional to the absolute temperature keeping the pressure constant”.

MATHEMATICAL REPRESENTATION:

Consider a gas confined in a container with volume “V” and Temperature “T” while the external pressure “P”.

Now according to Charles law:

 V ∞ T V = Constant x T V = KT V = K ——- (i) T

ANOTHER STATEMENT

According to eqn (i) we can also state Charles Law:

“At constant pressure the ratio between volume and absolute Temperature of any gas is always constant”.

GENERAL FORM OF CHARLES LAW:

Consider gas present in a container with temperature T1 and volume V1. When the temperature changes to T2, its volume also changes to V2.

Initially:

 V ∞ T V1 ∞ T1 V1 = Constant x T1 V1 = KT1 V1 = K ——- (A) T1

Finally

 V ∞ T V2 ∞ T2 V1 = Constant x T2 V1 = KT2 V2 = K ——- (B) T2

By comparing eq A and B

 V1 = V2 T1 T2

LIMITATION:

Charles law can’t be applicable at very low temperature between under such condition gas is converted into liquid state.

EXPLANATION WRT KMT:

According to KMT,

The KE of molecules of gas is directly proportional to the absolute temp. by increasing the temperature the KE of molecules increases so that molecules exert greater pressure on piston. Since external pressure is constant therefore piston moves in upward direction to increase the volume of gas.

GRAPH OF CHARLE’S LAW:

The graph between V and T is obtained as a straight line.

The temperature at which the volume of any gas becomes zero is -273oC or ZERO Kelvin, as shown in the graph.

ABSOLUTE ZERO:

It is the temperature above the point; all the gases condense to liquid so that gas behavior can no longer be observed. Its numerical value is -273oC or 0 Kelvin.

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