Answer to Question #155164 in General Chemistry for Alex

Question

Explain the factors that affect the chemical equilibrium of the following chemical reactions:

AgNO3 + NaCl → AgCl + NaNO3;

Na2CO3 + 2HCl → CO2 + NaCl + H2O.

N2 + 3H2 → 2NH3;

2SO2 + O2 → 2SO3.

Answer 1

1) AgNO_3(aq) + NaCl_(aq) → AgCl_(s) + NaNO_3(aq);

Reducing the concentration of any product shifts equilibrium to the right. Here AgCl precipitates, so the equilibrium is always shifted to the right and in equilibrium state there are only products. There are no gaseous substances so the change of pressure plays little part in the equilibrium state concentrations.

2) Na₂CO_3(aq) + 2HCl_(aq) → CO_2(g) + NaCl_(aq) + H₂O;

Same principle: gaseous CO₂ leaves the reaction container reducing its concentration in the reaction mixture and the equilibrium is always shifted to the right. In the equilibrium state there are only products. The equilibrium could be shifted to the left if pressure is applied: it will shift to favor the side of the reaction that involves fewer moles of gas.

3) N_2(g) + 3H_2(g) → 2NH_3(g);

Similarly, the equilibium is shifted to the right when pressure is applied. Reducing the concentration of NH_3(g) shifts equilibrium to the right. Reducing the concentration of H_2(g) or N_2(g) shifts equilibrium to the left.

4) 2SO_2(g) + O_2(g) → 2SO_3(g);

Similarly, the equilibium is shifted to the right when pressure is applied. Reducing the concentration of SO_3(g) shifts equilibrium to the right. Reducing the concentration of O_2(g) or SO_2(g) shifts equilibrium to the left.

1-4) Additionally, if the reaction is isothermal (heat is released in the reaction and the value of ΔH is negative) or endothermal (heat is absorbed in the reaction, and the value of ΔH is positive) we can picture heat as a reactant or a product and apply the same principles. If we raise the temperature on an endothermic reaction, it is essentially like adding more reactant to the system, and therefore, the equilibrium will shift to the right and lowering the temperature will shift the equilibrium to the left. For an exothermic reaction, increasing the temperature will shift the equilibrium to the left, while decreasing the temperature will shift the equilibrium to the right.