Exemplar Problems

Problem 6 : For the reaction:

N₂(g) + 3H₂(g) ⇌ 2NH₃(g) Kc = 4.0 x 10⁻³ at a certain temperature. If the initial concentration of N₂ is 0.1 M and the initial concentration of H₂ is 0.3 M, determine the equilibrium concentration of NH₃.

Solution :

Let’s denote the initial concentration of N₂ as [N₂]₀, the initial concentration of H₂ as [H₂]₀, and the equilibrium concentration of NH₃ as [NH₃]. We are given: [N₂]₀ = 0.1 M [H₂]₀ = 0.3 M Kc = 4.0 x 10⁻³

Using the balanced equation, we know that at equilibrium: [N₂] = [N₂]₀ - x [H₂] = [H₂]₀ - 3x [NH₃] = 2x

Now, we can write the expression for Kc: Kc = ([NH₃]²) / ([N₂]₀ - x)([H₂]₀ - 3x)³

Substitute the given values: 4.0 x 10⁻³ = (2x)² / (0.1 - x)(0.3 - 3x)³

Solve for x. Again, you can use numerical methods or a calculator to find the value of x.