For n moles of a gas the equation of state is given by, PV = n RT. If m and M be the mass and molecular weight of the gas, then n = m/M and the equation of statereduces to PV =m/MRT M or, P =mRT/MV At a fixed temperature (T = constant) if more amount of gas is added to a closed vessel (V = constant), then mass (m) of the gas increases. From the equation, it is evident that pressure of the gas increases.