When a gas expands at constant temperature, why does the pressure decrease? Explanin it on the basis of kinetic theory of gases.

Answer

When the gas expands at constant temperature, the average kinetic energy of the gas molecules remains the same. However, due to increase in volume of the gas, separation between the molecules increases. As a result the number of molecules colliding per second aganist the walls decreases. consequently less momentum is transferred to the walls of the container per seond. Hence the pressure exerted by the gas decreases.