Q8 (MC) At 400 K, the equilibrium constant for the reaction is Kp 7.0. A closed
ID: 561056 • Letter: Q
Question
Q8 (MC) At 400 K, the equilibrium constant for the reaction is Kp 7.0. A closed vessel at 400 K is charged with 1.00 bar of Br2, 1.00 bar of Cl2, and 2.00 bar of BrCl. Use Q to determine which of the statements below is true. A) The equilibrium partial pressures of Br2, Ch, and BrCl will be the same as the initial values. B) The equilibrium partial pressure of Br2 will be greater than 1.00 bar. C) At equilibrium, the total pressure in the vessel will be less than the initial total pressure D) The equilibrium partial pressure of BrCl will be greater than 2.00 bar E) The reaction will go to completion since there are equal amounts of Br2 and C12.Explanation / Answer
Ans. #Step 1: Calculate partial pressure:
Total pressure in vessel = 1.00 atm + 1.00 atm + 2.00 atm = 4.00 atm
Partial pressure of a gas = Pressure of the specified gas / Total pressure in vessel
pBr2 = 1.00 atm / 4.00 atm = 0.25
pCl2 = 1.00 atm / 4.00 atm = 0.25
pBrCl = 2.00 atm / 4.00 atm = 0.50
# Now,
Reaction quotient, Qp = (pBrCl)2 / (pBr2 x pCl2) = (0.50)2 / (0.25 x 0.25) = 4.0
When-
Qp > Kp, the reaction goes in backward direction (to the left). So,[reactants] increase whereas [product] decreases.
Qp < Kp, the reaction goes in forward direction (to the right). So, the [reactants] decreases whereas [Product] increases.
Qp = Kp, the reaction is at equilibrium. No change.
# Given, Kp = 7.0
Since, Qp < Kp , concertation of reactants, Br2 and Cl2 decreases and that of product BrCl increase because the reaction proceeds in forward direction.
# Correct option is- D. Due to formation of BrCl2, the equilibrium pressure of BrCl2 would be greater than its initial pressure 2.0 atm.
# Option A. Incorrect. The equilibrium pressure of Br2 and Cl2 would be lower than the initial pressure. And, that of BrCl2 would be greater than its initial pressure.
Option B. Incorrect. Since the reaction proceed in forward direction, the equilibrium partial pressure of Br2 would be lower than initial pressure (1.0 atm).
Option C. Incorrect. Since 2 mol reacts react to form 2 mol product, the total initial pressure is equal to total equilibrium pressure.
Option E. Incorrect. The reaction will go to completion since there are equal amount of Br2 and Cl2. The reaction never goes to completion. It only proceeds in forward direction to establish the equilibrium value Kp = 7.0. At that point, there must be some amount of all the chemical species including Br2 and Cl2.
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