Equilibrium Constant Calculator
Calculate Kc or Kp for chemical reactions. Automatically excludes pure solids and liquids from the expression.
*Pure Solids (s) and Liquids (l) are automatically excluded from the calculation.
Equilibrium Expression
Result will appear here
Mastering Chemical Equilibrium
Understand how reactions balance products and reactants.
In many chemical reactions, the reactants don't just turn into products and stop. Instead, the reaction goes in both directions—forward and backward—until the rate of both reactions is equal. This state is called Dynamic Equilibrium. The Equilibrium Constant (K) tells us the ratio of products to reactants at this stable point.
The Law of Mass Action
For a reversible reaction:
The Equilibrium Constant expression is:
Heterogeneous Equilibrium
Ignore Solids (s) & Liquids (l)
Pure solids and liquids have a constant concentration (density), so they are omitted from the K expression (effectively treated as 1).
*Only Aqueous (aq) and Gaseous (g) species are included.
Le Chatelier's Principle
If you change the conditions (concentration, pressure, temperature) of a system at equilibrium, the system will shift its position to counteract the change and find a new equilibrium.
Change Concentration
- • Add Reactant: Shift Right (make products)
- • Remove Product: Shift Right (make more)
Change Pressure
(Gases Only)
- • Increase Pressure: Diff towards side with fewer gas moles.
- • Decrease Pressure: Shift towards side with more gas moles.
Change Temperature
- • Exothermic (-ΔH): Heat is a "product". Adding heat shifts Left. K decreases.
- • Endothermic (+ΔH): Heat is a "reactant". Adding heat shifts Right. K increases.
Explore More Chemistry Tools
Frequently Asked Questions
Did I calculate K correctly if it's huge?
Often yes. Reactions that go to completion (like combustion) have K values of 10¹⁰ or more. It just means at equilibrium, there are virtually no reactants left.
What is the difference between Kc and Kp?
Kc uses Molar concentrations (mol/L), usually for aqueous solutions. Kp uses Partial Pressures (atm), strictly for gases. They are related by Kp = Kc(RT)^Δn.
Does a catalyst change K?
No! A catalyst speeds up both the forward and reverse reactions equally. It helps you reach equilibrium faster, but it does NOT change the position of equilibrium (K represents the same ratio).
Why are solids ignoed?
The 'concentration' of a solid is proportional to its density, which doesn't change regardless of how much solid you have. Since it's a constant, it's rolled into the K constant itself.
What if K = 1?
It means the concentration of products and reactants at equilibrium are roughly comparable. Neither side is strongly favored.
What is Reaction Quotient (Q)?
Q is calculated exactly like K, but using CURRENT concentrations, not necessarily equilibrium ones. Comparing Q to K tells you which way the reaction will shift to reach equilibrium.
Can K be negative?
No. Concentrations cannot be negative, so their ratio (product/reactant) must always be positive.
Is K temperature dependent?
Yes! Temperature is the ONLY factor that changes the value of K itself. Changing pressure or concentration shifts the position, but K stays constant (at constant T).