Select the single best answer.

Consider the following reaction and its equilibrium constant at [tex]100^{\circ}C[/tex]:
[tex]\[ N_2O_4(g) \rightleftharpoons 2 NO_2(g) \quad K_{eq} = 6.5 \][/tex]

If [tex]0.250 \, mol[/tex] of each reactant and product is mixed into a [tex]1.0 \, L[/tex] container, will the reaction proceed in the forward or reverse direction, or is it already at equilibrium?

A. The reaction will proceed in the forward direction.
B. The reaction is already at equilibrium.
C. The reaction will proceed in the reverse direction.



Answer :

To solve this problem, we need to determine if the reaction will proceed in the forward direction, reverse direction, or if it is already at equilibrium by comparing the reaction quotient ([tex]\( Q_c \)[/tex]) to the equilibrium constant ([tex]\( K_{eq} \)[/tex]).

### Step-by-Step Solution:

1. Write the balanced chemical equation for the reaction:

[tex]\[ N_2O_4(g) \rightleftharpoons 2 NO_2(g) \][/tex]

2. Identify the equilibrium constant [tex]\( K_{eq} \)[/tex]:

[tex]\[ K_{eq} = 6.5 \][/tex]

3. Determine the initial concentrations of the reactants and products:

Given:
- [tex]\( 0.250 \)[/tex] mol of [tex]\( N_2O_4 \)[/tex] in a [tex]\( 1.0 \)[/tex]-L container
- [tex]\( 0.250 \)[/tex] mol of [tex]\( NO_2 \)[/tex] in a [tex]\( 1.0 \)[/tex]-L container

Since the volume of the container is [tex]\( 1.0 \)[/tex] L, the molarity (concentration) is the same as the number of moles:
- [tex]\([N_2O_4] = 0.250 \, \text{mol/L}\)[/tex]
- [tex]\([NO_2] = 0.250 \, \text{mol/L}\)[/tex]

4. Calculate the reaction quotient [tex]\( Q_c \)[/tex]:

The expression for the reaction quotient [tex]\( Q_c \)[/tex] for the given reaction is:

[tex]\[ Q_c = \frac{[NO_2]^2}{[N_2O_4]} \][/tex]

Substitute the initial concentrations:

[tex]\[ Q_c = \frac{(0.250 \, \text{mol/L})^2}{0.250 \, \text{mol/L}} = \frac{0.0625}{0.250} = 0.25 \][/tex]

5. Compare [tex]\( Q_c \)[/tex] with [tex]\( K_{eq} \)[/tex]:

- [tex]\( Q_c = 0.25 \)[/tex]
- [tex]\( K_{eq} = 6.5 \)[/tex]

Since [tex]\( Q_c < K_{eq} \)[/tex]:

[tex]\[ 0.25 < 6.5 \][/tex]

6. Determine the direction of the reaction:

- If [tex]\( Q_c < K_{eq} \)[/tex], the reaction will proceed in the forward direction (towards the products) to reach equilibrium.
- If [tex]\( Q_c > K_{eq} \)[/tex], the reaction will proceed in the reverse direction (towards the reactants) to reach equilibrium.
- If [tex]\( Q_c = K_{eq} \)[/tex], the reaction is already at equilibrium.

In this case, since [tex]\( Q_c < K_{eq} \)[/tex], the reaction will proceed in the forward direction.

### Conclusion:

The reaction will proceed in the forward direction.