A system of propane and n-butane exists in two phase vapor / liquid equilibrium at 10 bar and 323 K. The mole fraction of propane in the vapor phase is 0.67 and 0.40 in the liquid phase. Additional pure propane is added to the system and the system is brought again to equilibrium at 10 bar and 323 K. What is the effect of the propane addition on the mole fractions of propane in the vapor and liquid phases? Explain your answer.