Question

If volume changes (for example, piston is pushed down or moved up), how would the total pressure change (T=constant)? How would mole fraction of the components change: in vapor? in liquid?

Answer 1

1. First we consider a piton cylinder assembly.
2. When we push the piston down, the pressure in the cylinder increases while when we move the piston up the pressure in the tank decreases.Because according to ideal gas Law and other equation of states the volume and pressure are inversly propotional when Temperature T is constant.
3. Now the composition and mole fraction in liquid and vapor phase depends on the the other factors also such as volatility of the components
4. In general from Raults Law When we increase the Pressure the mole fraction of any volatile component A in Liquid Phase increases while in Vapor Phase decreases
5. And also When we decrease  mole fraction of any volatile component A in Liquid Phase decreaseswhile in Vapor Phase increases.
6. The above things is happening because the temperature is constant. The Vaopor pressure of the components at this Temperature will be constant. But when we increase the Pressure the stauration temperature also get increases but our temperature is constant So the component whose volatility is less than the other got condensed and therefore its mole fraction in Liquid phase increases while in vapor phase decreases.So Ultimnately when Volume decreases the Pressure increase and when pressure increases mole fraction in liquid phase increases while in vapor phase decrease. And when Volume increases the Pressure decreases and the molefreaction in liquid phase decreases while in vapor phase increases.