Thermo Lecture 5

Question 1

What is a phase diagram?

Answer 1

A diagram that shows the stable phase assemblagesas a function of intensive properties of interest e.g. P, T, μ

Question 2

Why is the gradient of the line (on a graph of G against T) for a gas phase greater than the gradient of the line for the liquid phase

Answer 2

dG/dT is equal to -S (entropy). Gas phase have higher availability of equivalent microstates, greater entropy and therefore a steeper gradient.

Question 3

State the Clapeyron Equation

Answer 3

(dP/dT)σ = ΔS/ΔV = ΔHphase transition/TΔV

Question 4

What is the Clapeyron Equation used for?

Answer 4

To calculate the slope of the phase boundary curve for a pure substance

Question 5

What is the bubble point line?

Answer 5

The line on a P-V diagram indicating where the first bubble of vapour is evolved

Question 6

What is the dew point line?

Answer 6

The line on a P-V diagram indicating where the final drop of liquid is present at the transition of liquid to gas

Question 7

What is a tie-line?

Answer 7

A line on a P-V diagram of constant pressure showing the affect of volume at a phase transition. It is related to the proportion of the phases

Question 8

Give the equation for degrees of freedom. What does it represent?

Answer 8

f = c + 2 - Φ
c = number of components
Φ = number of phases
f = number of variables that can be changed independently without changing the number of phases present.

Question 9

What is retrograde condensation?

Answer 9

Where hit dew point line twice and left with a saturated vapour? not sure about this

Question 10

What assumptions are made for the Clausius-Clapeyron Equation?

Answer 10

the volume of the vapour is significantly greater than the volume of the liquid and that ideal gas behaviour is appropriate