Chemistry Practice Problems The Reaction Quotient Practice Problems Solution: Given that Kp = 1.39 at 400°C for the reaction, P4...

Solution: Given that Kp = 1.39 at 400°C for the reaction, P4(g) <=> 2 P2(g), which answer best describes the reaction when 1.50 mol of P4(g) and 1.15 mol of P2(g) are mixed in a 25.0 L, closed container at 400°C? [REMEMBER: it’s Kp] a. Qp = 1.95, the reaction proceeds to the left.b. Qp = 1.95, the reaction proceeds to the right.c. Qp = 0.51, the reaction proceeds to the left.d. Qp = 0.51, the reaction proceeds to the right.e. Qp = 0.77, the reaction proceeds to the left.

Problem

Given that Kp = 1.39 at 400°C for the reaction, P4(g) <=> 2 P2(g), which answer best describes the reaction when 1.50 mol of P4(g) and 1.15 mol of P2(g) are mixed in a 25.0 L, closed container at 400°C? [REMEMBER: it’s Kp

a. Qp = 1.95, the reaction proceeds to the left.
b. Qp = 1.95, the reaction proceeds to the right.
c. Qp = 0.51, the reaction proceeds to the left.
d. Qp = 0.51, the reaction proceeds to the right.
e. Qp = 0.77, the reaction proceeds to the left.

Solution

We’re being asked to determine what happens to the reaction when 1.50 mol of P4(g) and 1.15 mol of P2(g) are mixed in a 25.0 L closed container at 400 °C.

P4(g) ⇌ 2 P2(g);            Kp = 1.39 

We will use the reaction quotient, Q, to determine if a chemical reaction would be at equilibrium or not. The formula for Q is:

Q=productsreactants

Depending on if Q is greater than or less than K our reaction will shift to attain equilibrium by reaching the equilibrium constant K:

If Q = K           → the reaction is at equilibrium
If Q < K           → the reaction shifts in the forward direction to reach equilibrium
If Q > K           → the reaction shifts in the reverse direction to reach equilibrium


Since the Kp is given, we need to calculate the pressure of each gas first using the ideal gas equation:

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