For all gases, Cp - Cv = R. This ,R is the

Mechanical work =pΔVFor one mole of a gas at temperature TpV=RTAt constant pressure, when temperature isincreased by 1° volume increases (say by ∆V), then p(V+ΔV)=R(T+1)∴pV+pΔV=RT+R∴pΔV=R