Explain the effect of changes of temperature, concentration and pressure on chemical systems at equilibrium by applying collision theory to the forward and reverse reactions.

A sealed container holds the following reversible reaction at equilibrium at 400 K: \( \text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \quad \Delta H = -92 \, \text{kJ mol}^{-1} \) Explain, using collision theory, why increasing the concentration of \( \text{N}_2(g) \) causes the equilibrium position to shift to the right.