Equation and purpose
Ratio of product/reactant concentrations at equilibrium.
\[K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}\]
Ratio of product/reactant concentrations at equilibrium.
REARRANGEMENTS
—
Dimensional check: M ratio ✓
Variables and units
| Symbol | Quantity | Unit | Notes |
|---|---|---|---|
| Kc | Kc | — | — |
| [X] | [X] | — | — |
Conditions and limitations
Pure solids/liquids omitted; Kc function of T only.
Worked example
N2+3H2→2NH3 Kc=[NH3]²/([N2][H2]³).
Equilibrium Constant Kc
Ratio of product/reactant concentrations at equilibrium.
Equation
Inline: $K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$$
Variables
| Symbol | Quantity | Unit | Notes |
|---|---|---|---|
| equilibrium constant | — or M^Δn | — | |
| equilibrium concentration | M | — |
Conditions and limitations
Pure solids/liquids omitted; Kc function of T only.
Rearrangements
—
Dimensional check: M ratio ✓
Worked example
N2+3H2→2NH3 Kc=[NH3]²/([N2][H2]³).
Steps: write equation → substitute with units → check dimensional consistency → report with correct significant figures.
Common errors
- Including solids
- Using initial instead of equilibrium concentrations
Related resources
- chemical-equilibrium topic
- Calculators — linked only when a real calculator implements this formula.
- Constants — sourced constants with version when values are required.
Sources
- NIST Physical Constants 2022 — CODATA.
Reviewed 2026-08-21 by Editorial Team; due 2027-08-21.
Common errors
- Including solids
- Using initial instead of equilibrium concentrations
RELATED FORMULAS
C
Chemistry Fundamentals Editorial TeamAuthor
E
Editorial Review BoardReviewer
Editorial Team — transparent review placeholder
Reviewed August 21, 2026
SOURCES
- [nist-2022]NIST Physical Constants 2022 (2022). NISThttps://physics.nist.gov/constants