Question

At a certain temperature and total pressure of 105 Pa, iodine vapour contains 40% by volume of $\text {I}$ atoms
$I_2 (g) ⇋ 2I (g)$
Calculate Kp for the equilibrium.

Answer 1

Partial pressure of I atoms,
$P_I = \frac {40}{100} × P_{total}$

$P_I= \frac {40}{100} × 10^5$
$P_I = 4 × 10^4 \ Pa$
Partial pressure of I2 molecules,
$P_{I_2} = \frac {60}{100} × P_{total}$

$P_{I_2} = \frac {60}{100} × 10^5$
$P_{I_2} = 6 × 10^4 \ Pa$
Now, for the given reaction,
$K_p = \frac {(p_I)^2}{P_{I_2}}$

$K_p = \frac {(4 × 10^4)^2\ Pa^2 }{6 × 10^4\ Pa}$
$K_p = 2.67 × 10^4\ Pa$