Question

1. The value of KC for the thermal decomposition of hydrogen sulfide, shown below, is 2.2 × 10-4 at 1400 K.
2H2S(g) ⇌ 2H2(g)+ S2(g)
A sample of gas in which [H2S] = 3.60 M is heated to 1400 K in a sealed vessel. After chemical equilibrium has been achieved, what is the value of [H2S]? Assume no H2 or S2 was present in the original sample. answer in M

Answer 1

$2H_2S(g) \leftrightarrow 2H_2(g) + S_2(g)$

Make ICE table

$[H_2S]$ $[H_2]$ $[S_2]$

Initial 3.60 0 0

Change -x +x +0.5x

Equilibrium 3.60-x x 0.5 x

$K_c = \frac{[H_2]^2[S_2]}{[H_2S]^2}$

$2.2\times 10^{-4} = \frac{(x^2)(0.5x)}{(3.60-x)^2}$

make an assumption that 3.60-x = 3.60

$2.2\times10^{-4} = \frac{(x^2)(0.5x)}{(3.60)^2}$

$x=0.179$

$[H_2S] = 3.6-0.179 = 3.421 M$