Question

Molar heat capacity of water in equilibrium water $\rightleftharpoons$ vapours at constant pressure is:

• A. zero
• B. Infinity
• C. $\frac{80}{18}cal/mol$
• D. $\frac{540}{18}cal/mol$

Answer 1

The correct option is B Infinity

We know,
$C_p={\left(\frac{\partial H}{\partial T}\right)}_p;$
At equilibrium T is constnat,
which means $\partial T$ tends to 0.
which means,
molar heat capacity at equilibrium is infinity.

Practical Aspect:
Also we can understand the when phase changing is taking place all the energy supplied will be used for phase conversion and no temperture raise will take place despite providing so much energy thus heat capacity will become infinite.