For example we had a closed system with water at 298K, so it's pressure is 0.031atm. To it we add a gas, A such that we get 1atm of total pressure. That gas undergoes a phase transition at 1.5atm and 298K. So initially, the partial pressure of water is a little smaller than 0.031atm due to the dissolution of some of that gas, and the rest of the pressure is from that gas. As we compress this mixture of gases with 2atm of pressure what would happen? How would the A and water's partial pressure change? Since A is able to increase its partial pressure further before liquefying, I feel that it should increase to 1.5atm. But that results in a decrease in the water's partial pressure because it's mole fraction in the liquid continues to drop further. So the total pressure will be 1.5atm from A, and less than 0.031atm from water. But then since we're applying 2atm of pressure, how does that equal out? Something like the uploaded image but instead of air we replace it with a different gas.