Equilibrium Constant Calculator
Simplify chemical equilibrium calculations with examples.com's Equilibrium Constant Calculator. Accurate, quick, and easy to use!
How to Use the Equilibrium Constant Calculator
- Enter the coefficient and equilibrium concentration for Reactant 1.
- Enter the coefficient and equilibrium concentration for Reactant 2.
- Enter the coefficient and equilibrium concentration for Product 1.
- Enter the coefficient and equilibrium concentration for Product 2.
- Click “Calculate” to see the equilibrium constant (Kc) instantly.
Features of the Equilibrium Constant Calculator
- Calculates Kc for any reversible reaction with up to two reactants and two products.
- Accounts for stoichiometric coefficients as exponents, matching the law of mass action.
- Works with decimal concentrations for precise lab data.
- Instant, live results as you type.
- Free to use with no sign-up required.
Equilibrium Constant Formula
The equilibrium constant (Kc) expresses the ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised to the power of its stoichiometric coefficient.
Kc = ([Product 1]^coefficient × [Product 2]^coefficient) ÷ ([Reactant 1]^coefficient × [Reactant 2]^coefficient)
A large Kc value means the equilibrium favors products, while a small Kc value means it favors reactants.
Equilibrium Constant Reference Table
| [R1]^coeff | [R2]^coeff | [P1]^coeff | [P2]^coeff | Kc |
|---|---|---|---|---|
| 2¹ | 3¹ | 4¹ | 5¹ | 3.333333 |
| 0.5² | 0.2¹ | 0.8¹ | 0.3² | 1.44 |
| 1.5¹ | 0.6² | 2.0¹ | 0.9¹ | 3.333333 |
| 0.4¹ | 0.4¹ | 0.6² | 0.5¹ | 1.125 |
How to Calculate the Equilibrium Constant
To calculate Kc, raise each equilibrium concentration to the power of its coefficient in the balanced equation, multiply the product terms together, multiply the reactant terms together, then divide the product total by the reactant total.
Suppose Reactant 1 has a coefficient of 1 and concentration of 2, Reactant 2 has a coefficient of 1 and concentration of 3, Product 1 has a coefficient of 1 and concentration of 4, and Product 2 has a coefficient of 1 and concentration of 5.
Kc = (4¹ × 5¹) ÷ (2¹ × 3¹) = 20 ÷ 6 ≈ 3.333333.
Solved Examples on Equilibrium Constant
1. Equal Coefficients
Example: R1 = 2 (coeff 1), R2 = 3 (coeff 1), P1 = 4 (coeff 1), P2 = 5 (coeff 1).
Kc = (4 × 5) ÷ (2 × 3) = 20 ÷ 6 ≈ 3.333333.
2. Mixed Coefficients With Decimals
Example: R1 = 0.5 (coeff 2), R2 = 0.2 (coeff 1), P1 = 0.8 (coeff 1), P2 = 0.3 (coeff 2).
Kc = (0.8¹ × 0.3²) ÷ (0.5² × 0.2¹) = 0.072 ÷ 0.05 = 1.44.
3. Higher Reactant Coefficient
Example: R1 = 1.5 (coeff 1), R2 = 0.6 (coeff 2), P1 = 2.0 (coeff 1), P2 = 0.9 (coeff 1).
Kc = (2.0¹ × 0.9¹) ÷ (1.5¹ × 0.6²) = 1.8 ÷ 0.54 ≈ 3.333333.
4. Higher Product Coefficient
Example: R1 = 0.4 (coeff 1), R2 = 0.4 (coeff 1), P1 = 0.6 (coeff 2), P2 = 0.5 (coeff 1).
Kc = (0.6² × 0.5¹) ÷ (0.4¹ × 0.4¹) = 0.18 ÷ 0.16 = 1.125.
1. What is the equilibrium constant (Kc)?
Kc is a number that expresses the ratio of product concentrations to reactant concentrations at chemical equilibrium, with each concentration raised to the power of its coefficient in the balanced equation.
2. What does a large or small Kc value mean?
A Kc greater than 1 means the equilibrium favors products, meaning more product forms than reactant remains. A Kc less than 1 means the equilibrium favors reactants, meaning the reaction doesn’t proceed very far forward.
3. Why are concentrations raised to a power in the Kc formula?
Each concentration is raised to the power of its stoichiometric coefficient from the balanced chemical equation, since that coefficient reflects how many moles of that substance are involved in the reaction.
4. Does Kc change with concentration?
No. Kc is constant for a given reaction at a given temperature, regardless of the starting concentrations used. Changing the initial amounts shifts the equilibrium position, not the value of Kc itself.
5. Does temperature affect Kc?
Yes. Kc is only constant at a fixed temperature. Changing the temperature of the system changes the value of the equilibrium constant.
6. What’s the difference between Kc and Kp?
Kc uses molar concentrations of reactants and products, while Kp uses their partial pressures. Kp is typically used for reactions involving gases.