Question

The pressure of moist gas at a given temperature is 10 mm Hg at volume $V$. Aqueous tension at this temperature is 3 mm Hg. Find the final pressure of gas at the same temperature if the volume is reduced to 1/3 of the original volume.

Answer 1

The moist gas has pressure = 10 mm Hg, and aqueous tension = 3 mm Hg

$\Rightarrow$ pressure dry gas = 10-3 = 7 mm Hg

Now, volume V is reduced to V/3.

In constant T (isothermal process):-

$P_1{V}_1=P_2{V}_2$

$\Rightarrow 7\times V=P_2.\frac{V}{3}\Rightarrow P_2=21$ mm Hg. [Partial pressure of dry gas]

As it exists in moist form, final pressure = $21+3=24$ mm Hg

(aqueous tenstion adds up)