Here we go again, which shows that my foundation in physical chemistry is really poor! But I still came to figure it out.
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At a certain temperature, pure liquid A and pure liquid B form an ideal liquid mixture, with P*B > P*A. When the gas and liquid phases are in equilibrium, the composition of B in the gas phase, yB(), is A) greater than its composition in the liquid phase, xB; B) less than its composition in the liquid phase, xB; C) equal to its composition in the liquid phase, xB; D) it may be either greater or less than its composition in the liquid phase, xB. Which option do you think is correct? How can one determine the saturated vapor pressure of a liquid in a phase diagram? Let me thank everyone first! :P
For an ideal liquid mixture, P = Pa + Pb = PaXa + PbXb, and yb = Pb/P = PbXb/(PaXa + PbXb). Therefore, yb – Xb = PbXb/(PaXa + PbXb) – Xb = …… After simplifying by finding a common denominator, we get (Pb – Pa) * Xb * (1 – Xb) / (PaXa + PbXb). Since Pb – Pa > 0, Xb > 0, and 1 – Xb > 0, it follows that yb – Xb > 0, meaning yb > Xb. Thus, the correct answer is (A); it’s quite simple! Proving inequalities for grade 10 in high school!
Okay! Thanks! :lol
The formula on the 3rd floor is correct, but it can be improved slightly: when comparing the values, we have yb/xb = Pb*/(Pa*xa + Pb*xb) > Pb*/(Pb*xa + Pb*xb) = 1, which means yb > xb
Well, not bad, another method then. But I still have a question: how can one determine the saturated vapor pressure of a substance in a phase diagram?
In the p-x diagram of the gas-liquid equilibrium pressures for the A-B two-component system, at the far left end the molar fraction of component B is 0, which correspondingly represents the saturated vapor pressure of pure component A. Similarly. On the far right is PB*, so go and check a book on physical optimization.
Qualitative analysis is sufficient; B is a volatile component, so it must be true that yb > 0.5 and xb < 0.5, hence yb > xb.
Okay, okay, thank you! I’ll take a good look at it:P