Problems and Solutions on Thermodynamics and Statistical Mechanics

Thermodynamic a 129

(c) From L = T(S1 - S2), we have

As dS1 = -dT CP 1 - alVldp, where a1 = - (s) ,, we have

T Vl

TJsing

L

dP -

dT T(V1 - V2) '

_-

we obtain

dL L L

dT - = T 1- (CPI - C,,) - (alvl - a2V2)- Vl - v2.

(d) Let 1 and 2 stand for water and vapor respectively.

From V2 >> V1, we know

where 012 = 1/T, so AL = (Cpl - C,,)AT.

2

9

Letting C,, = 1 cal/g "C, C,, = -R cal/g.OC, AT = 10°C, we get

AL = 6 cal/g.

1132

(a) Derive an expression for the dependence of the equilibrium vapor

pressure of a material on the toal pressure (i.e., how does the equilibrium

partial pressure of a material depend on the addition of an overpressure of

some inert gas?).

(b) Use this result to discuss qualitatively the difference between the

triple point and the ice point of water.

( was co nsin)