Equilibrium Calculations in Chemistry
- As discussed previously, the equilibrium constant ($ K $) provides a numerical measure of the balance between reactants and products at equilibrium.
- For a general reaction: $$
aA + bB \rightleftharpoons cC + dD
$$ - The equilibrium constant expression is: $$
K = \frac{[C]^c [D]^d}{[A]^a [B]^b}
$$ Here:- $ [... ] $ represents molar concentrations.
- The exponents correspond to the stoichiometric coefficients in the balanced equation.
For the reaction $ N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) $, the equilibrium constant expression is:$$
K = \frac{[\text{NH}_3]^2}{[\text{N}_2][\text{H}_2]^3}
$$
Step-by-Step: Calculating Equilibrium Concentrations
To calculate equilibrium concentrations, follow these steps:
- Write the $ K $ Expression:
- Start by writing the equilibrium constant expression for the reaction.
- Define Initial and Equilibrium Concentrations:
- Use an ICE (Initial, Change, Equilibrium) table to organize the data.
- Define the initial concentrations, the changes during the reaction, and the equilibrium concentrations.
- Substitute into the $ K $ Expression:
- Substitute the equilibrium concentrations into the $ K $ expression, often in terms of $ x $, the change in concentration.
- Solve for $ x $:
- Solve the resulting equation to find $ x $, representing the change in concentration.
