LT#4: Qc Calculations & Le Chatelier's Principle

Question 1

What is the difference between Qc and Kc?

Answer 1

Kc must be calculated with concentrations at equilibrium. Qc you are not sure if they are at equilibrium.

Question 2

How do you calculate Qc?

Answer 2

[products]/[reactants] raised to their coefficients in the balanced chemical equation.

Question 3

If Qc is > Kc…

Answer 3

The system has excess products. The reverse reaction will go faster to reach equilibrium.

Question 4

If Qc is = Kc…

Answer 4

The system is already at equilibrium. Forward and reverse reactions are the same speed.

Question 5

If Qc is < Kc…

Answer 5

The system has excess reactants. The forward reaction will go faster to reach equilibrium.

Question 6

What does Le Châtelier’s Principle state?

Answer 6

An equilibrium will respond to relieve the effect of any change in the conditions that affect the system.

Question 7

How does the Common Ion Effect cause a Le Châtelier shift?

Answer 7

Adding one of the chemicals involved in the equilibrium will cause a shift to remove the excess.

Removing one of the chemicals causes a shift to replace it.

Question 8

How does changing the temperature cause a Le Châtelier shift?

Answer 8

Adding or removing energy from the system will cause a shift to return it back to its original amount.

Question 9

How does changing the pressure cause a Le Châtelier shift?

Answer 9

Must have an imbalance of gas particles left side vs. right side.

If pressure is increased, the system will shift to reduce the number of gas particles to relieve the excess pressure.

If pressure is decreased, it will move to make more particles to replace the pressure lost.