Chemistry: Equilibrium Math Question 5

Question

A closed vessel is charged with 0.23 bar of hydrogen gas and allowed to react with excess I₂(s) at 25 C.

H₂(g) + I₂(s) ↔ 2 HI(g)

What is the final equilibrium pressure of HI(g) in the vessel? K_P = 0.284

Answer 1

This is what I came up with:

First, let’s set up the equilibrium expression

K_p = (P_HI)²/P_H

Second, we set up an ICE table; note we don’t include the I₂ because it is a solid and we are dealing with pressures

	H2	HI
Initial	.23	0
Change	-x	+2x
Equilibrium	.23 – x	2x

Our equilibrium expression becomes

2x²/(.23 - x) = .284

We now have a quadratic equation. The two roots are x = .0971 and x = -0.168

The second root leads to impossible values (more H₂ and a negative amount of HI) so the first root leads to our solution.

P_H2 =.133

P_HI = .194