SOLUTION TO EXERCISE 18


(a) Rivers and lakes probably could not exist, because 270 K is lower
than the 273K of the triple point.  However, since the solid-liquid 
boundary has negative slope, if it's shallow enough then the pressure
of 0.1 atm may be above the line at 270 K, and indeed it could be liquid.
That slope is not known in this problem, so it could go either way.
Either answer is defensible as long as the reasoning is thorough and sound;
further observation and experimentation will be needed!

(b) P = 0.1 atm; V = 0.45 l; R = 0.0821 l atm/mole K; T = 270 K.

The ideal gas law gives PV=NRT; thus,

   N = PV/RT = 2.0 * 10^-3 moles = 0.002 * 6 * 10^23 = 1.2 * 10^21 molecules.