Vapour-Liquid Equilibrium P2

Question 1

How do we measure VLE data experimentally?

Answer 1

Using a Recirculating Still

Question 2

What is the other name for ‘K factor’ and give the general formula

Answer 2

Vaporisation Equilibrium Ratio

Ki=yi/xi

Question 3

Give the equation for K1 in a binary mixture

Answer 3

K1=y1/x1

Question 4

Give the equation for K2 in a binary mixture

Answer 4

K2=(1-y)/(1/x)

Question 5

Give the equation for relative volatility

Answer 5

alpha= K1/K2 = y(1-x)/x(1-y)

Question 6

For constant pressure, whats the trend as temp increases?

Answer 6

alpha decreses

Question 7

At critical point what happens to relative volatility?

Answer 7

It tends to 1, meaning that you can’t separate the components

Question 8

Give the equation for geometric mean

Answer 8

sqrt(a(x=0)a(x=1))

Better to write down

Question 9

Give the Raoult’s Law expression for total pressure

Answer 9

P=x1P1* + x2P2*

Question 10

Give the Raoult’s Law expression for the mole fraction of the vapour phase

Answer 10

yi=xiPi*/P

Question 11

write the K factor in terms of Raoult’s Law

Answer 11

Ki=Pi*/P

Question 12

What is an azeotropic mixture?

Answer 12

Azeotrope: Point at which liquid and vapour have the same composition

Question 13

What leads to negative deviations from Raoult’s law?

Answer 13

Strong attractions between unlike molecules. The total pressure is less than ideal and can lead to maximum-boiling temp azeotrope

Question 14

What leads to positive deviations from Raoult’s law?

Answer 14

Unfavourable (attract less) interactions between unlike molecules. Total pressure is greater than ideal and can lead to minimum-boiling temp azeotrope.