Question

Some pale yellow crystals of ammonium nitrite (NH4NO2) were placed in an empty, sealed flask at Time 0. The ammonium nitrite crystals began to decompose according to the chemical equation shown below.

NH4NO2(s) + heat ⇌ N2(g) + 2 H2O(g)

At Time T1, the temperature of the system was decreased, and equilibrium was then allowed to re-establish. The new equilibrium was established at Time E2.

1. How would the value of the equilibrium constant (K) at E2 compare to the value at E1? Explain your answer. Justify your answer using Le Chatelier’s Principle.

2. Explain, in terms of collision theory, the effect of the temperature decrease on the rate of both the forward and reverse reactions, from T1 to E2.

Answer 1

1. The value of the equilibrium constant (K) at E2 would be lower than the value at E1. This is because according to Le Chatelier's Principle, when a system at equilibrium is subjected to a change in temperature, the system will shift in the direction that opposes the change in temperature. In this case, decreasing the temperature would cause the system to shift towards the reactants side in order to increase the temperature, which would result in a decrease in the concentration of the products and an increase in the concentration of the reactants. As a result, the value of the equilibrium constant would decrease.

2. According to collision theory, the rate of a chemical reaction is dependent on the frequency and energy of collisions between the reactant molecules. When the temperature of a system is decreased, the average kinetic energy of the molecules decreases, resulting in a decrease in the frequency of collisions between the reactant molecules. As a result, the rate of both the forward and reverse reactions would decrease from T1 to E2. However, since the reverse reaction involves the breaking of a bond, which requires more energy than the formation of a bond, the decrease in the rate of the reverse reaction would be greater than the decrease in the rate of the forward reaction. Therefore, the system would shift towards the reactants side to establish a new equilibrium, resulting in a decrease in the concentration of the products and an increase in the concentration of the reactants.

Step-by-step explanation: