Reaction Quotient Calculator

Reaction Quotient Calculator

The Reaction Quotient Calculator computes $Q$ for a reversible reaction at any point in time and compares it with the equilibrium constant $K$ to predict reaction direction.

For $a\text{[A]} + b\text{[B]} \rightleftharpoons c\text{[C]} + d\text{[D]}$:

$$Q = \frac{[\text{C}]^c \times [\text{D}]^d}{[\text{A}]^a \times [\text{B}]^b}$$

When $Q < K$, the reaction proceeds forward toward products. When $Q > K$, it proceeds in reverse. When $Q = K$, the system is at equilibrium.

Example: For $\text{Cd}^{2+} + 4\text{Cl}^- \rightleftharpoons \text{CdCl}_4^{2-}$ with $[\text{Cd}^{2+}] = 1$, $[\text{Cl}^-] = 0.5$, $[\text{CdCl}_4^{2-}] = 0.25$ M and $K = 10^8$:

$$Q = \frac{0.25}{1 \times 0.5^4} = 4$$

Since $Q = 4 \ll K$, the reaction strongly favors the forward direction.

Related tools: Equilibrium Constant Calculator, Concentration Calculator, and Chemical Entropy Calculator.