Heat Capacity of gases
Specific and molar heat capacity of gases
Specific heat (or heat capacity) of a substance may be defined as the quantity of heat required to raise the temperature of 1 g of that substance by . it is expressed in calories or joules. Molar heat capacity may be defined as :
Molar heat capacity = Sp. Heat × Mol. Mass
Since the gases expand on heating, hence molar heat capacity of gases is termed as follows:
(i) Molar heat capacity at constant pressure (Cp): it is the amount of heat in calories required to raise the temperature of one mole of a gas through at constant pressure, while the volume is allowed to increase.
(ii) Molar heat capacity at constant volume (Cv): it is the amount of heat in calories required to raise the temperature of one mole of a gas through at constant volume, while the pressure is allowed to increase.
With the help of kinetic gas euation it is calculated that,
(for mono atomic gas)
And Cp – Cv = R
= = 1.66
It means that ratio of Cp and Cv is equal to 1.66 for mono atomic gases.
This ratio changes with the atomicity of the gas. Its general equation is given below:
For any gas;
where X = 0, R and 3/2 R for mono-, di- and poly-atomic gases. By putting the value of X in the above equation, the ratio comes to 1.66, 1.40 and 1.33 for mono-, di- and poly-atomic gases, respectively.
The value indicates the atomicity of the gases; hereby atomic weight of the gas can be calculated as:
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