HUMAT 2018 Q 47 equilibrium constant

Practice Question Solving
1

Hydrogen is made industrially by reacting methane and water (steam), as shown in the equation below:
CH4(g) + H2O(g) ⇌ 3H2(g) + CO(g) ΔH = +206 kJ / mol
Which one of the following statements about the reaction above is correct?

A) At a higher temperature (at constant pressure) the equilibrium constant increases and the position of equilibrium shifts to the right.

B) At a higher temperature (at constant pressure) the equilibrium constant decreases and the position of equilibrium shifts to the right.

C) At a lower pressure (at constant temperature) the equilibrium constant decreases and the position of equilibrium shifts to the right.

D) At a lower pressure (at constant temperature) the equilibrium constant increases and the position of equilibrium shifts to the right.

E) A nickel catalyst has no effect on the equilibrium constant but shifts the position of
equilibrium to the right.

Hi everyone,

The answer is A).
I agree that A) is correct, but why is D) incorrect??
If the pressure decreases the equilibrium should shift to the right (side with the most gas particles thus increasing the pressure).
Thus the equilibrium constant should increase: k = [products]/[reactants] if [reactants] decreases then k increases
What is wrong about my reasoning?

Thanks!

2

According to Le Chatelier’s principle, when the pressure is increased, the equilibrium will shift in the direction that reduces the total number of moles of gas. In this case, it would shift to the left, which makes reverse reaction happen and reducing the production of hydrogen gas.

Therefore, at a lower pressure (at constant temperature), the equilibrium constant would not increase, and the position of equilibrium would not shift to the right. The correct answer should describe a decrease in the equilibrium constant and a shift to the left.

In addition, equilibrium constant changes only whenthere is a change in temperature; therefore, A, B would experience K change but C and D won’t.

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