Question

Predict the direction in which each of the following equilibria will shift if the pressure on the system is decreased by expansion. (a) \(\mathrm{Ni}(s)+4 \mathrm{CO}(g) \rightleftharpoons \mathrm{Ni}(\mathrm{CO})_{4}(g)\) (b) \(2 \mathrm{CH}_{4}(g) \rightleftharpoons \mathrm{C}_{2} \mathrm{H}_{2}(g)+3 \mathrm{H}_{2}(g)\) (c) \(\mathrm{Br}_{2}(g)+\mathrm{H}_{2}(g) \rightleftharpoons 2 \mathrm{HBr}(g)\)

Short answer

Question: Predict the direction in which the chemical equilibrium will shift in response to a decrease in pressure for the following reactions: a) Ni(s) + 4 CO(g) ↔ Ni(CO)4(g) b) 2 CH4(g) ↔ C2H2(g) + 3 H2(g) c) Br2(g) + H2(g) ↔ 2 HBr(g) Answer: a) The equilibrium will shift to the left (toward more moles of gas). b) The equilibrium will shift to the right (toward more moles of gas). c) There will be no shift in the equilibrium as the number of moles of gas is the same on both sides.

Step-by-step solution

(Step 1: Identify the number of moles of gas on both sides of the reaction for Ni(s) + 4 CO(g) ↔ Ni(CO)4(g))

In reaction (a), there are 4 moles of CO gas on the left side and 1 mole of Ni(CO)4 gas on the right side.

(Step 2: Determine the direction of the shift for reaction (a))

According to Le Chatelier's Principle, when the pressure on the system decreases by expansion, the system adjusts to counteract the imposed change by increasing the total number of moles of gas. In this case, the system will shift to the left side (toward more moles of gas) to restore equilibrium.

(Step 3: Identify the number of moles of gas on both sides of the reaction for 2 CH4(g) ↔ C2H2(g) + 3 H2(g))

In reaction (b), there are 2 moles of CH4 gas on the left side and a total of 4 moles of gas (1 mole of C2H2 and 3 moles of H2) on the right side.

(Step 4: Determine the direction of the shift for reaction (b))

Since the pressure is decreasing, the system will adjust itself to increase the total number of moles of gas. In this case, the equilibrium will shift to the right side (toward more moles of gas) to restore equilibrium.

(Step 5: Identify the number of moles of gas on both sides of the reaction for Br2(g) + H2(g) ↔ 2 HBr(g))

In reaction (c), there are 2 moles of gas on the left side (1 mole of Br2 and 1 mole of H2) and 2 moles of HBr gas on the right side.

(Step 6: Determine the direction of the shift for reaction (c))

In this case, the number of moles of gas on both sides of the equation is the same. Therefore, when the pressure is decreased, there will be no change in the position of the equilibrium. The system will not experience any shift in either direction.