18.4 Reaction Quotient (slides)

18.4 Reaction Quotient

By Lan Vu

​How do we know a system is at equilibrium?

​Equilibrium:

• the rate of the forward and reverse reactions are the same​

• the amount of products and reactants are constant

​

SO, how do we know if a system is at equilibrium?

We use the reaction quotient, Q

​Reaction Quotients

Multiple Choice

The value of the equilibrium constant, K_p for the reaction below is 3.1 × 10^-4 at 700K.

N₂ (g) + 3H₂ (g) ↔ 2NH₃ (g)

Given the initial partial pressure of the gases, P_N2 = 0.411 atm; P_H2 = 0.903 atm; P_NH3 = 0.224 atm, calculate the value of the reaction quotient, Q.

• Q = 0.0437

• Q = 0.1658

• Q = 0.6036

• Q = 0.1352

​Explanation: The value of the equilibrium constant, K_p for the reaction below is 3.1 × 10^-4 at 700K.

N₂ (g) + 3H₂ (g) ↔ 2NH₃ (g)

Given the initial partial pressure of the gases, P_N2 = 0.411 atm; P_H2 = 0.903 atm; P_NH3 = 0.224 atm, calculate the value of the reaction quotient, Q.

Multiple Choice

The value of the equilibrium constant, K_p for the reaction below is 3.1 × 10^-4 at 700K.

N₂ (g) + 3H₂ (g) ↔ 2NH₃ (g)

Given the initial partial pressure of the gases, P_N2 = 0.411 atm; P_H2 = 0.903 atm; P_NH3 = 0.224 atm. Predict the direction in which the reaction will proceed at 700 K.

• Since Q > K_p, the equilibrium will proceed to the left to bring the value Q down to 3.1 × 10^-4.

• Since Q > K_p, the equilibrium will proceed to the right to bring the value Q down to 3.1 × 10^-4.

• Since Q > K_p, the equilibrium will proceed to the left to bring the value Q up to 3.1 × 10^-4.

• Since Q > K_p, the equilibrium will proceed to the right to bring the value Q up to 3.1 × 10^-4.

​Explanation: The value of the equilibrium constant, K_p for the reaction below is 3.1 × 10^-4 at 700K.

N₂ (g) + 3H₂ (g) ↔ 2NH₃ (g)

Given the initial partial pressure of the gases, P_N2 = 0.411 atm; P_H2 = 0.903 atm; P_NH3 = 0.224 atm. Predict the direction in which the reaction will proceed at 700 K.

​1) solve for Q ( you did that in the slide before)

2) Place the Q and K on a number line and draw an arrow from Q to K. What direction does the arrow point to is the direction the equilibrium will proceed.