High School Chemistry  ·  Practice by Skill

Chemical Equilibrium Practice Problems

A reaction reaches equilibrium when the forward and reverse rates match, so the amounts stop changing even though both reactions are still running. The equilibrium constant K tells you where that balance sits. Practice below covers writing K, comparing Q to K, ICE tables, and shifts from Le Chatelier's principle.

What you’ll practice

  • Writing and calculating K: build the K expression from a balanced equation and plug in concentrations.
  • Q versus K: predict which way a mixture will shift to reach equilibrium.
  • ICE tables: track initial, change, and equilibrium amounts to find an unknown concentration.
  • Le Chatelier's principle: predict how changes in concentration, pressure, or temperature move the equilibrium.

Learn the method first →

A quick example: K and Q

For N2 + 3 H2 ⇌ 2 NH3, products go on top and each concentration is raised to its coefficient: K = [NH3]2 ÷ ([N2][H2]3).

Calculate Q with the same expression using the current concentrations, then compare. If Q is less than K, there are too few products.

When Q < K, the reaction shifts toward the products (to the right).

3 free chemical equilibrium problems

Give each one a real try before you open the solution. Your answer is checked as soon as you submit it, and the worked solution shows every step so you can see exactly where a setup went wrong.

#1Calculating K
For H2(g) + I2(g) ⇌ 2 HI(g), at equilibrium: [H2] = 0.220 M, [I2] = 0.220 M, [HI] = 1.54 M. Calculate the equilibrium constant K.
#2Dynamic Equilibrium
At dynamic equilibrium in a closed system, which of the following is true?
#3ICE Table
For CO(g) + H2O(g) ⇌ CO2(g) + H2(g), K = 1.60. Initial: [CO]0 = 0.500 M, [H2O]0 = 0.400 M, [CO2]0 = [H2]0 = 0. Set up an ICE table and find [CO2] at equilibrium.

Questions you might have about chemical equilibrium

What is the equilibrium constant K?
K is the ratio of product concentrations to reactant concentrations at equilibrium, each raised to its coefficient. A large K means products are favored and a small K means reactants are favored. Pure solids and liquids are left out.
What is the difference between Q and K?
Q has the same form as K but uses the concentrations at any moment, not just at equilibrium. Comparing Q to K tells you which direction the reaction will move.
How do I use an ICE table?
Write the initial concentrations, then the change in terms of x using the coefficients, then the equilibrium values as initial plus change. Substitute them into the K expression and solve for x.
What is Le Chatelier's principle?
If you disturb a system at equilibrium, it shifts to partly undo the disturbance. Adding a reactant shifts it toward the products, and removing a product does the same.
High School Chemistry · Chemical Equilibrium Practice Problems