Problems and Solutions on Thermodynamics and Statistical Mechanics

1118

Estimate the surface tension of a liquid whose heat of vaporization is

(Columbia)

10" ergs/g (250 cal/g).

Solution:

The surface tension is the free energy of surface of unit area; therefore
the surface tension is a = Qrp, where Q is the heat of vaporization, r
is the thickness of the surface (r = lov8 cm) and p is the liquid density
(p = 1 g/cm3). Thus

1119

Put letters from a to h on your answer sheet. After each put a T or

an F to denote whether the correspondingly numbered statement which

follows is true or false.

(a) The liquid phase can exist at absolute zero.

(b) The solid phase can exist at temperatures above the critical tem-

(c) Oxygen boils at a higher temperature than nitrogen.

(d) The maximum inversion temperature of He is less than 20 K.

(e) 7 of a gas is always greater than one.

(f) A compressor will get hotter when compressing a diatomic gas than

perature.

wheacompressing a monatomic gas at the same rate.

(g) The coefficient of performance of a refrigerator can be greater than

one.

(h) A slightly roughened ball is thrown from north to south. As one

looks down from above, the ball is seen to be spinning counterclockwise.

The ball is seen to curve toward east.

( wis c 0 ns in)