Question

Calculate the following:

a. The bubble point temperature of a liquid mixture with a molar composition of 45.0 mol% n-hexane and 55.0 mol% n-heptane at 1.00 atm and the composition (mole fractions) of the vapor in equilibrium with this mixture.

Bubble Point:  _____°C

yHexane:  _____

yHeptane:  _____

b. The dew-point temperature of a gas mixture with a molar composition of 30.0% n-hexane, 35.0% n-heptane, and 35.0% air at 1.00 atm and the composition (mole fractions) of the liquid in equilibrium with this mixture.

Dew Point:  _____°C

xHexane:  _____

xHeptane:  _____

Answer 1

Solution to question (a)

We will make use of ideal gas law for this problem

Let n-Hexane be component 1 and n-heptane be component 2

Now we will write ideal gas law for both of this component

Y1*P = X1*P1sat ..........1

Y2*P= X2*P2sat ..........2

Adding equation 1 and 2 we get

(Y1 + Y2) *P = X1*P1sat + X2*P2sat .........3

for binary mixture we know that Y1 + Y2 =1 and X1+ X2 =1

Substituting above two relations in equation 3

P = X1 *P1sat + (1-X1)*P2sat ..........4

we will require Antoine equation for hexane and heptane

From standard data

where P is in mmHg and T is in^oC

X1 = and X2 = 0.35

also P = 1 atm = 760 mmHg

substituting these in equation 4 we get

P = X1 *P1sat + (1-X1)*P2sat ..........4

solving the above equation for T we get,

T =80.686 ^oC

P1sat =1084.18 mmHg

P2sat = 437.91 mmHg

substituting these values in equation 1 to obtain Y1

Y1*760 = 0.45*1084.18

Y1 =0.65

Y2 = 1-0.65 = 0.35