Consider a molecule `A` in the bulk of a vessel as shown in fig. This molecule is surrounded by other molecules in symmetrical manner, with the result that this molecule on the whole experiences no net force of attraction. Now, consider a molecule `B` near the side of the vessel, which is about to strike one of its sides, thus contributing towards the total pressure of the gas. There are gas molecules only on one side of the vessel, i.e. towards its centre, with the result that this molecule experiences a net force of attraction towards the centre of the vessel. This results in decreasing the velocity of the molecule, and hence its momentum. Thus, the molecule does not contribute as much force as it would have, had there been no force of attraction. Thus, the pressure of a real gas would be smaller than the corresponding pressure or an ideal gas, i.e. `p_i = P_r + text(correction term)`
This correction term depends upon two factors :
When these expressions are substituted in the ideal gas equation `p_i V_i = nRT`, we get
`(p+ (n^2 a)/V^2)(V - nb) = nRT`
This equation is applicable to real gases and is known as the Van der Waals equation.
Consider a molecule `A` in the bulk of a vessel as shown in fig. This molecule is surrounded by other molecules in symmetrical manner, with the result that this molecule on the whole experiences no net force of attraction. Now, consider a molecule `B` near the side of the vessel, which is about to strike one of its sides, thus contributing towards the total pressure of the gas. There are gas molecules only on one side of the vessel, i.e. towards its centre, with the result that this molecule experiences a net force of attraction towards the centre of the vessel. This results in decreasing the velocity of the molecule, and hence its momentum. Thus, the molecule does not contribute as much force as it would have, had there been no force of attraction. Thus, the pressure of a real gas would be smaller than the corresponding pressure or an ideal gas, i.e. `p_i = P_r + text(correction term)`
This correction term depends upon two factors :
When these expressions are substituted in the ideal gas equation `p_i V_i = nRT`, we get
`(p+ (n^2 a)/V^2)(V - nb) = nRT`
This equation is applicable to real gases and is known as the Van der Waals equation.