Define the term chemical equilibrium - NSC Physical Sciences - Question 6 - 2019 - Paper 2

To calculate the equilibrium constant Kc, we use the formula:

$K_c = \frac{[CO]^2}{[CO_2]}$

Given that at equilibrium:

• Concentration of CO2 = 0,054 mol·dm⁻³
• Concentration of CO = 0,813 mol·dm⁻³ (since it is produced in a 2:1 ratio as per the balanced equation).

Substituting in, we have:

$K_c = \frac{(0,813)^2}{0,054} \approx 12,24 \; (range: 11,85 - 12,66)$

Using the concentration of CO2 and the balanced equation, we first determine the amount of moles of CO2:

$n(CO_2) = c \times V = 0,054 \; \text{mol/dm}^3 \times 3 \; \text{dm}^3 = 0,162 \; ext{mol}$

According to the balanced reaction, for every mole of CO2, 1 mole of C(s) is required. Therefore, the minimum moles of C(s) is:

$n(C) = n(CO_2) = 0,162 \; ext{mol}$

Now, converting moles to mass:

Mass of C(s) = m = n × molar mass = 0,162 mol × 12 g/mol = 1,94 g.

If more carbon is added to the container, according to Le Chatelier's principle, the system will respond by shifting the equilibrium position to the right to produce more CO(g). Therefore, the amount of CO(g) will INCREASE.

Increasing the pressure favors the side of the reaction with fewer moles of gas. In this case, the right side (product side) has 2 moles of CO(g) for every 1 mole of CO2(g) utilized. Therefore, the reverse reaction is favored, resulting in a DECREASE in the amount of CO(g).

From the table, we observe that as the temperature increases, the percentage of CO(g) increases while the percentage of CO2(g) decreases. According to Le Chatelier's principle, if increasing temperature favors the endothermic reaction. Therefore, we can conclude that the reaction is ENDOTHERMIC.