Question

The values for $H_{vap}$ and $S_{vap}$ for ethanol are respectively 4 kJ and 2 J/K. The boiling point of ethanol will be:

• A. 2000 K
• B. 4000 K
• C. 5000 K
• D. none of these

Answer 1

Answer: (A)

2000 K

Solution:- (A) $2000K$

As we know that,

$\Delta G=\Delta H-T\Delta S$

At boiling point, the reversible process $\text{liquid}\rightleftharpoons \text{vapour}$ is in equilibrium at one atmospheric pressure.

$\therefore \Delta G=0$

$\Rightarrow \Delta H=T\Delta S$

$\Rightarrow T=\frac{\Delta H}{\Delta S}$

Given:-

$\Delta H=4kJ=4000J$

$\Delta S=2J/K$

$\therefore T=\frac{4000}{2}=2000K$

Hence the boiling point of ethanol is $2000K$.