1. Chapter 18: Chemical Equilibrium
Table of Contents
Chapter 18: Chemical Equilibrium
18.2: Factors affecting chemical equilibrium

2. Factors Affecting Chemical Equilibrium
Chemical Equilibrium: Basic Concepts
Factors Affecting Chemical Equilibrium
Le Châtelier’s principle: If a system at equilibrium is stressed, it will shift to reduce the stress.
Rule of Thumb: “Same side does the opposite, opposite side does the same”
Equilibrium shifts in the direction that increases after the change.

3. Factors Affecting Chemical Equilibrium
Chemical Equilibrium: Basic Concepts
Factors Affecting Chemical Equilibrium
Equilibrium can be disturbed by 3 factors:
1. Changing concentration: adding or removing a reactant or product.
2. Changing temperature
3. Changing volume & pressure

4. Factors Affecting Chemical Equilibrium
Chemical Equilibrium: Basic Concepts
Factors Affecting Chemical Equilibrium
1. Changing Concentration: Removing a Reactant or a Product
Adding a reactant makes it form more products , causes the equilibrium to shift to the right
Adding the product makes it form more reactant, causes a shift to the left

5. Factors Affecting Chemical Equilibrium
Chemical Equilibrium: Basic Concepts
Factors Affecting Chemical Equilibrium
1. Removing a Reactant or a Product
Removing/diluting a reactant makes it form more reactants, causes the equilibrium to shift to the left
Removing/diluting the product makes it form more product, causes a shift to the right

6. Practice adding and removing:
How will it effect equilibrium if you…
Add NO?
shifts to the right, forms more products
Add Br2?
shifts to the right, forms more products
Add NOBr?
shifts to the left, forms more reactants
Remove NOBr?
shifts to the right, forms more products
Remove Br2?
shifts to the left, forms more reactants
Remove NO?
shifts to the left, forms more reactants

7. 2. Changes in temperature
Chemical Equilibrium: Basic Concepts
2. Changes in temperature
Changes in temperature, causes a shift in equilibrium by changing the value of Keq.
In contrast, changes in concentration or pressure cause a shift in equilibrium without changing Keq

8. 2. Changes in temperature
Chemical Equilibrium: Basic Concepts
2. Changes in temperature
Treat heat as any other reactant or product
Exothermic = heat is a product
Reactants ↔ Products + heat
Endothermic = heat is a reactant
Reactants + heat ↔ Products

9. 2. Changes in temperature
Chemical Equilibrium: Basic Concepts
2. Changes in temperature
Increase in temp
shift to left, Keq decreases
Decrease in temp
shift to right, Keq increases

10. Practice changes in temp:
heat + 6CO2(g) + H2O(l) = C6H12O6(aq) + 6O2(g)
How will it effect equilibrium if you…
Increase temperature
shift to the right, Keq increases
Decrease temperature
shift to the left, Keq decreases

11. 3. Changes in volume & pressure
Chemical Equilibrium: Basic Concepts
3. Changes in volume & pressure
In a gaseous system, volume and pressure are interconnected.
↓ volume, ↑ pressure
↑ volume, ↓ pressure
Shift to side with fewest moles
Shift to side with most moles

12. 3. Changes in volume & pressure
Chemical Equilibrium: Basic Concepts
3. Changes in volume & pressure
How will this reaction respond to the following changes:
Increase in pressure
shift to right
Increase in volume
shift to left

13. Practice changes in vol & press:
How would increasing the volume of the reaction vessel impact each of these equilibria?
shift to the left
shift to the right

14. Practice changes in vol & press:
How would increasing the pressure of the reaction vessel impact each of these equilibria?
shift to the right
shift to the left

15. 3. Changes in volume & pressure
Chemical Equilibrium: Basic Concepts
3. Changes in volume & pressure
When molesreactants = molesproducts
volume and pressure have no effect on equilibrium.