Equilibrium Shift

Question

4 NH3(g) + 5 O2(g) ↔ 4 NO(g) + 6 H2O(g) ΔH = -904.4 kJ

How does each of the following changes affect the yield of NO at equilibrium? Answer increase, decrease, or no change: a) increase [NH3]; b) increase [H2O]; c) decrease [O2]; d) decrease the volume of the container in which the reaction occurs; e) add a catalyst; f) increase temperature.

Answer 1

4 NH₃(g) + 5 O₂(g) <==> 4 NO(g) + 6 H₂O(g) .. ΔH = -904.4 kJ



All of the following answers are based on Le Chatelier's Principle. If you are unsure about this principle, you should read up on it and understand that whenever a stress or change is placed on a system at equilibrium the system will react to reduce or eliminate that stress. This is Le Chatelier's principle.

(a). Increasing [NH₃] will INCREASE yield of NO.

(b). Increasing [H₂O] will DECREASE yield of NO.

(c). Decreasing [O₂] will DECREASE yield of NO.

(d). Decreasing the volume will DECREASE yield of NO. Reason is that decreasing the volume will increase the pressure and since there are more moles of gas on the product side, the equilibrium will shift toward the reactants (right) thus decreasing the yield of NO.

(e). Adding a catalyst will have no effect on the yield of NO. It will only increase the RATE of the reaction.

(f). Increasing the temperature will DECREASE yield of NO Reason is that since the reaction is exothermic (negative value for ∆H), heat is a product and increasing temperature will thus shift the equilibrium back towards the reactants, thus reducing yield of NO.