AP Chem Q vs K reaction quotient practice questions

Define the reaction quotient (Q).

Q is the ratio of the concentrations of products to reactants at any point in a reaction: $\displaystyle Q = \frac{[C]^c[D]^d}{[A]^a[B]^b}$.

What does K represent in a chemical reaction?

K is the equilibrium constant, defined as the ratio of the concentrations of products to reactants at equilibrium: $\displaystyle K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$.

True or False: Q can exceed K.

True. Q can be greater than K, indicating the reaction will shift left towards reactants to reach equilibrium.

When Q < K, what happens to the system?

The system will shift right, favoring the formation of products until equilibrium is reached.

Compare Q and K for a reaction at equilibrium.

At equilibrium, Q = K. They represent the same ratio of concentrations.

Calculate Q for the reaction: 2A + B ⇌ C.

If [A] = 0.5 M, [B] = 0.2 M, and [C] = 0.3 M, then $\displaystyle Q = \frac{[C]}{[A]^2[B]} = \frac{0.3}{(0.5)^2(0.2)} = 6.$

Define Kc and Kp.

Kc uses molarity (M) for concentrations, while Kp uses partial pressures (atm) for gaseous reactions.

What is the relationship between Kp and Kc?

Kp and Kc are related by the equation $\displaystyle Kp = Kc(RT)^{ riangle n}$, where $\displaystyle R$ is the gas constant, $\displaystyle T$ is temperature in K, and $\displaystyle riangle n$ is the change in moles of gas.

True or False: K changes with concentration changes.

False. K is constant at a given temperature, regardless of concentration changes.

When Q = K, what is the system's status?

The system is at equilibrium, with no net change in concentrations of reactants and products.

Fill in the blank: If Q decreases, the reaction shifts ______.

right, favoring the formation of products.

What is the significance of Q and K in predicting direction?

They help determine whether a reaction will proceed forward (towards products) or reverse (towards reactants) to reach equilibrium.

Calculate K for the reaction: A + 2B ⇌ 3C.

At equilibrium, if [A] = 0.1 M, [B] = 0.2 M, [C] = 0.5 M, then $\displaystyle K = \frac{[C]^3}{[A][B]^2} = \frac{(0.5)^3}{(0.1)(0.2)^2} = 62.5.$

Describe the effect of temperature on K.

K changes with temperature. For endothermic reactions, K increases with rising temperature; for exothermic, K decreases.

What is the unit for Kc?

Units of Kc depend on the reaction. For $\displaystyle aA + bB ⇌ cC + dD$, it is $\displaystyle M^{(c+d-a-b)}$.

If Q = 0.8 and K = 0.5, what will happen?

The reaction will shift left (towards reactants) to reach equilibrium since Q > K.

What happens to Q if products increase?

Q increases, indicating a shift in equilibrium to the left to re-establish balance.

True or False: K changes with concentration.

False. K is constant at a given temperature, regardless of concentration changes.

Decrease in pressure leads to...

A shift toward more moles of gas in equilibrium.

Fill in the blank: If Q < K, the reaction shifts _____ to reach equilibrium.

right (toward products)

Comparing Q and K: Q < K means?

The reaction will favor the formation of products to reach equilibrium.

Example: At equilibrium, K = 0.5. Q = 0.2. Shift direction?

Right towards products to increase Q.

What effect does increasing temperature have on an exothermic reaction?

Shifts equilibrium left, decreasing product concentration.

True or False: K is affected by catalysts.

False. Catalysts speed up reactions but do not change equilibrium constant K.

If Q = K, the system is...

at equilibrium, with no net change in concentrations.

Cause → Effect: Adding a reactant results in...

A shift to the right, producing more products.

What is the effect of removing a product?

Equilibrium shifts right to produce more product.

Decrease in temperature affects an endothermic reaction by...

Shifting equilibrium left, favoring reactants.

If Q > K, the reaction shifts...

Left to favor reactants.

Example: N₂(g) + 3H₂(g) ⇌ 2NH₃(g); K = 0.1. If Q = 0.5, what happens?

The reaction shifts left towards N₂ and H₂.

What effect does increased volume have on gas reactions?

Shifts equilibrium toward the side with more moles of gas.

What is the relationship between Q and K at equilibrium?

They are equal (Q = K).

Removing a reactant affects Q how?

Q increases, potentially shifting equilibrium to the left.

True or False: K varies with pressure changes.

False. K remains constant; pressure changes affect Q.

Effects of dilution on Q and K?

- Q decreases - K remains unchanged.

Real-world example of Q and K application?

Consider the Haber process: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). - Q < K: Shift right, more NH₃. - Q = K: System at equilibrium. - Q > K: Shift left, decrease NH₃.