Question

NO2 and N2O4 undergo the reaction shown. When a sealed

Answer 1

Answer:

• Option C) The rates of the forward and reverse reactions are equal.

Explanation:

NO₂ and N₂O₄ undergo the following equilibrium reaction:

• 2NO₂(g)   ⇄     N₂O₄(g)

That is a reversible reaction, i.e. there are two simultaneous reactions: the direct or forward reaction and the reverse reaction:

• Direct reaction: 2NO₂(g)     →   N₂O₄(g)

• Reverse reaction: 2NO₂(g)  ←   N₂O₄(g)

At the beginning, only NO₂(g) is in the sealed container. The NO₂ concentration is maximum, and the rate of the forward reaction is maximum.

As the reaction progresses, the concentration of NO₂ diminishes, and, consequently, the rate of the forward reaction decreases.

As soon as the N₂O₄ appears, the reverse reaction starts. At the beginning the rate is low, but as the N₂O₄ concentration increases the rate of the reverse reaction increases.

When both forward and reverse rates become equal the equilibrium has been reached. This is what is called a dynamical equilibrium.

Then, as per the choices, you have that, at equilibrium:

A) No N₂O₄ is present:

• False: as explained above, at equilibrium both NO₂ and N₂O₄ are present.

B) No chemical reactions are occurring.

• False: as explained above, at equilibrium both forward and reverse reaction are occurring at the same rate.

C) The rates of the forward and reverse reactions are equal.

• True: as explained, this is the meaning of dynamic equilibrium.

D) The maximum number of molecules has been reached.

• False: the number of molecules of each compound at equilibrium will be given by the constant of equiibrium, Keq = [N₂O₄] / [NO₂]², and this value varies with the temperature.