Calculating the Equilibrium Constant with Coefficients

Nisarg Shah 1C
Posts: 54
Joined: Sat Jul 22, 2017 3:00 am

Calculating the Equilibrium Constant with Coefficients

Why do you raise each species in the equilibrium constant to its coefficient because when doing an ICE table you already add/subtract the change by the coefficient times x?

For example, for 3H2 + N2 --> 2NH3, why do you raise the coefficent to each species after you already subtract or add by -3x or +2x.
H2 N2 NH3
I 1 1 0
C 1-3x 1-x +2x
E 1-3x 1-x 2x

Nancy Dinh 2J
Posts: 59
Joined: Fri Sep 29, 2017 7:07 am

Re: Calculating the Equilibrium Constant with Coefficients

Nisarg Shah 1C wrote:Why do you raise each species in the equilibrium constant to its coefficient because when doing an ICE table you already add/subtract the change by the coefficient times x?

For example, for 3H2 + N2 --> 2NH3, why do you raise the coefficent to each species after you already subtract or add by -3x or +2x.
H2 N2 NH3
I 1 1 0
C 1-3x 1-x +2x
E 1-3x 1-x 2x

It's because the 1-3x, 1-x, and 2x are the concentrations of H2, N2, and NH3. We know that $K = \frac{[NH_{3}]^{2}}{[H_{2}]^{3}\cdot [N_{2}]}$. Now it is simply substitution. $K = \frac{(2x)^{2}}{(1-3x)^{3}\cdot (1-x)}$

Aliza Ajmal 1D
Posts: 25
Joined: Fri Sep 29, 2017 7:05 am

Re: Calculating the Equilibrium Constant with Coefficients

The coefficient before the x, like 3x for NH3, is referring to the number of moles of NH3. When using x in the ICE chart for equilibrium, make sure to remember the number of moles of each component and tack it on as a coefficient to x. Also, you don't always add x to the reactants side. When Q (reaction quotient) is bigger than K, you would subtract on the reactant side, and add x to the reactant side when Q is smaller than K. I made the mistake of adding x to the wrong side and it made me mess up a problem so I thought it would be helpful to mention :)