The synthesis of methanol from carbon monoxide and hydrogen gas is described by the following chemical equation:
CO(g)+2H2(g)⇌CH3OH(g)
The equilibrium constant for this reaction at 25 ∘C is Kc=2.3×104. In this tutorial, you will use the equilibrium-constant expression to find the concentration of methanol at equilibrium, given the concentration of the reactants.

Determine the expression for the equilibrium constant, Kc, for the reaction by identifying which terms will be in the numerator and denominator:

The equilibrium-constant expression is a mathematical equation that can be rearranged to solve for any of the variables in it. Rearrange the equilibrium-constant expression to solve for [CH3OH].
[CH3OH]=[CH3OH]=
1Kc[CO][H2]2
Kc[CO][H2]2
Kc[CO][H2]2
[CO][H2]2Kc

Equilibrium constant is defined as the ratio of concentration of products to the concentration of reactants each raised to the power their stoichiometric ratios. It is expressed as [tex]K_{c}[/tex]

[tex]aA+bB\rightleftharpoons cC+dD[/tex]

[tex]K_{c}=\frac{[C]^c[D]^d}{[A]^a[B]^b}[/tex]

[tex]CO(g)+2H_2(g)[/tex] ⇌ [tex]CH_3OH(g)[/tex]

The equilibrium-constant expression for the given reaction is given by:

[tex]K_{c}=\frac{[CH_3OH]}{[CO][H_2]^2}[/tex]

If we are given with equilibrium constant and equilibrium concentration of carbon monoxide and hydrogen gas we can determine the concentration of methanol at equilibrium.

The expression will be given as:

[tex][CH_3OH]=K_c\times [CO]\times [H_2]^2[/tex]