Equilibrium Constant Calculator

Q: What is the relationship between K and delta-G?

dG-deg = -RT ln K. At 298 K: dG-deg = -5.71 x log K (kJ/mol). Spontaneous (dG 1.

Calculate Kc equilibrium constant from equilibrium concentrations. Find K from molar concentrations of products and reactants using the equilibrium expression for any reaction.

⚖️ Equilibrium📐 Kc = [C]^c[D]^d / ([A]^a[B]^b)🧪 Chemistry

Product concentration [C]^c (M^x)

Product concentration [D]^d (M^x)

Reactant concentration [A]^a (M^x)

Reactant concentration [B]^b (M^x)

Enter concentrations already raised to their stoichiometric powers. e.g., for aA+bB to cC: enter [C]^c and [A]^a

Please enter valid values.

Formula & Reference

Variable	Symbol	Formula	Units
Equilibrium Constant Calculator	See formula	Kc = [C]^c[D]^d / ([A]^a[B]^b)	dimensionless

Step-by-Step Examples

Example 1

Simple Equilibrium

N2+3H2 to 2NH3 at equilibrium: [NH3]=0.200 M, [N2]=0.500 M, [H2]=0.300 M.

K = [NH3]^2/([N2][H2]^3)
K = (0.200)^2/((0.500)(0.300)^3)
K = 0.0400/(0.500x0.0270) = 0.0400/0.0135 = 2.96

✓ Kc = 2.96

Example 2

Large K Example

H2+I2 to 2HI: [HI]=0.786, [H2]=0.107, [I2]=0.107 M.

Kc = (0.786)^2/((0.107)(0.107)) = 0.618/0.01145 = 53.9

✓ Kc = 53.9 (products favored)

Example 3

Small K Example

PCl5 to PCl3+Cl2: [PCl5]=0.100, [PCl3]=0.020, [Cl2]=0.020.

Kc = (0.020)(0.020)/0.100 = 0.0040

✓ Kc = 0.0040 (reactants favored)

Real-World Applications

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Chemical Manufacturing

Equilibrium constants guide optimization of industrial reactions like Haber (NH3) and Contact (H2SO4) processes.

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Drug Binding

Drug-receptor binding constants are equilibrium constants that determine drug efficacy.

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Environmental Chemistry

Carbonate equilibrium in oceans (Kc for CO2/HCO3-/CO3^2-) controls ocean pH and CO2 absorption.

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Analytical Chemistry

Complexation equilibria (formation constants) determine metal speciation in solution.

Common Mistakes to Avoid

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Coefficients become powers

For aA+bB to cC: Kc = [C]^c/([A]^a[B]^b). If a=2: [A]^2 means square the concentration.

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Pure solids and liquids omitted

Do not include concentrations of pure solids (NaCl) or pure liquids (H2O) in the expression.

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K changes with temperature only

K is constant at a given temperature. Changing concentration, pressure, or catalyst does NOT change K.

Frequently Asked Questions

What does K tell us about equilibrium? ▾

K >> 1: products strongly favored. K ~ 1: comparable amounts. K << 1: reactants strongly favored. K = [products]/[reactants] at equilibrium only.

What is the relationship between K and delta-G? ▾

dG-deg = -RT ln K. At 298 K: dG-deg = -5.71 x log K (kJ/mol). Spontaneous (dG < 0) means K > 1.

How does K change with temperature? ▾

If reaction is exothermic, K decreases with T. If endothermic, K increases with T. From van Hoff equation: d(lnK)/dT = dH/RT^2.

What is the difference between Kc and Kp? ▾

Kc uses molar concentrations; Kp uses partial pressures. Kp = Kc(RT)^(delta-n) where delta-n = moles gas products - moles gas reactants.

What is an ICE table? ▾

Initial-Change-Equilibrium: tracks concentrations through equilibrium. Start with initial concentrations, set up algebraic expressions for changes, solve for equilibrium values.

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Formula Explorer connections

Interpretation: This formula describes how reactants, products, ions or phases distribute when opposing processes reach equilibrium. Assumption: Use equilibrium rather than initial concentrations, correct stoichiometric exponents, and the specified temperature; activities may replace concentrations in nonideal systems.

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