ΓΌ  Charle’s Law (Volume – Temperature Relationship): the volume of fixed mass of a gas is directly proportional to absolute temperature. Mathematically, it is written as

V Ξ± T

Or,      V = k2 x T

Or,      V/T = k2, a constant

Consider a fixed amount of gas at constant pressure P. Let V1 be its volume at a temperature T1 and V2 be its volume at a temperature T2.

Then according to Charle’s law:

V1/T1 = V2/T2

 If volume is plotted against temperature at constant pressure, the graph obtained is as follows.



Since the graph is obtained at constant pressure, it is called Isobar.

If we extend the graph to temperature axis (X-axis), the graph will meet at -273.150C. At this temperature, the volume of the gas becomes zero. This lowest hypothetical or imaginary temperature at which gases are supposed to occupy zero volume is called Absolute zero of temperature and the scale of temperature based on absolute zero is called Absolute scale of temperature. All gases become solid or liquid before reaching this temperature.

 

Note: 1. All gases obey Charle’s law at very low pressures and high temperatures. 

2. Boyle's and Charles’ law are examples of a limiting law, a law i.e. strictly true only in certain limit in this case p→0.






ΓΌ  Gay Lussac’s law: It states that at constant volume, pressure of a fixed amount of a gas is directly proportional to the temperature.

Mathematically,

p Ξ± T (V, n constant)

P/T  =  a constant

If we plot a graph between pressure and temperature of a fixed mass of gas at constant volume, the graph obtained is as follows: