1. 10.5 Changing Equilibrium Conditions: Le Châtelier’s Principle
The transport of oxygen involves an equilibrium between hemoglobin (Hb), oxygen, and oxyhemoglobin (HbO2). Hb(aq) + O2(g) HbO2(aq) For a person living at higher altitudes, hemoglobin concentration increases, causing a shift in the equilibrium back in the direction of HbO2 product.
Hypoxia may occur at high altitudes where the oxygen concentration is lower.
Learning Goal Use Le Châtelier’s Principle to describe the
changes made in equilibrium concentrations when the reaction conditions change.

2. Le Châtelier’s Principle
When the conditions of a reaction at equilibrium are changed, the forward and reverse reactions will no longer be equal. Le Châtelier’s principle states that when a stress is placed on a reaction at equilibrium, the system responds by changing the rate of the forward or reverse reaction in the direction that relieves that stress.

3. Le Châtelier’s Principle
The stress of adding water to tank A increases the rate of the forward direction to reestablish equal water levels and equilibrium. Core Chemistry Skill Using Le Châtelier’s Principle

4. Effect of Concentration Change on Equilibrium: Adding Reactant
Consider the following reaction at equilibrium:
H2(g) + I2(g) HI(g)
If more reactant (H2 or I2) is added,
the rate of the forward reaction increases to form more product until the system is again at equilibrium.
the equilibrium shifts toward the products.
Add H2

5. Effect of Concentration Change on Equilibrium

6. Effect of Concentration Change on Equilibrium: Removing Reactant
Consider the following reaction at equilibrium:
H2(g) + I2(g) HI(g)
If some of a reactant (H2 or I2) is removed,
the rate of the reverse reaction increases to form more reactant until the equilibrium is reached.
the equilibrium shifts toward the reactants.
Remove H2

7. Effect of Concentration Change on Equilibrium: Adding Product
Consider the following reaction at equilibrium:
H2(g) + I2(g) HI(g)
If more product (HI) is added,
the rate of the reverse reaction increases to form more H2 and I2 reactants.
the equilibrium shifts toward the reactants.
Add HI

8. Effect of Concentration Change on Equilibrium: Removing Product
Consider the following reaction at equilibrium:
H2(g) + I2(g) HI(g)
When some of the product (HI) is removed,
there is an decrease in collisions of HI molecules.
the rate of the forward reaction increases and forms more product (HI).
Remove HI

9. Effect of Concentration Change on Equilibrium

10. Effect of a Catalyst on Equilibrium
Adding a catalyst speeds up a reaction by lowering the activation energy, thus increasing the rate of the forward and reverse reactions.
The time to reach equilibrium is shorter; however, the same ratios of reactants and products are present.
The addition of a catalyst does not change the equilibrium mixture.

11. Effect of Volume Change on Equilibrium: Decreasing Volume
A change in the volume of a gas mixture at equilibrium will change the concentration of the gases in the mixture.
2CO(g) + O2(g) CO2(g)
Decreasing the volume increases the concentration of the gases, and the system shifts in the direction of the smaller number of moles to compensate.
Decrease Volume

12. Effect of Volume Change on Equilibrium: Increasing Volume
A change in the volume of a gas mixture at equilibrium will change the concentration of the gases in the mixture.
2CO(g) + O2(g) CO2(g)
Increasing the volume decreases the concentration of the gases, and the system shifts in the direction of the larger number of moles to compensate.
Increase volume

13. Effect of Volume Change on Equilibrium
(a) A decrease in the volume of the container causes the system to shift in the direction of fewer moles of gas. (b) An increase in the volume of the container causes the system to shift in the direction of more moles of gas.

14. Chemistry Link to Health: Hb
Oxygen transport involves an equilibrium between hemoglobin (Hb), oxygen, and oxyhemoglobin (HbO2).
Hb(aq) + O2(g) HbO2(aq)
When there is a high concentration of O2 in the alveoli of the lungs, the reaction shifts in the direction of oxyhemoglobin.
When the concentration of O2 is low in the tissues, the reverse reaction releases O2 from oxyhemoglobin.

15. Chemistry Link to Health: Hb
Given the reaction of hemoglobin,
Hb(aq) + O2(g) HbO2(aq)
At normal atmospheric pressure, oxygen diffuses into the blood because the partial pressure of oxygen in the alveoli is higher than that in the blood.
At altitudes above 8000 ft, a decrease in atmospheric pressure results in a lower pressure of O2.

16. Chemistry Link to Health: Hb
At an altitude of 18,000 ft, a person will obtain 29% less oxygen and may experience hypoxia.
Hypoxia may occur at high altitudes where the oxygen concentration is lower.

17. Chemistry Link to Health: Hb
According to Le Châtelier’s principle, a decrease in oxygen
shifts the equilibrium in the direction of the reactants.
depletes the concentration of HbO2, causing hypoxia.
Hb(aq) + O2(g) HbO2(aq)
Remove O2

18. Effect of Temperature Change on Equilibrium: Decreasing Temperature
Decreasing the temperature of an endothermic reaction
causes the system to respond by shifting the reaction toward more heat.
shifts the reaction toward the reactants, increasing heat in system.
N2(g) + O2(g) + heat NO(g)
Decrease Temperature

19. Effect of Temperature Change on Equilibrium: Increasing Temperature
Increasing the temperature of an endothermic reaction
causes the system to respond by shifting the reaction to remove heat.
shifts the reaction toward the products, using up the heat.
H2(g) + O2(g) + heat NO(g)
Increase Temperature

20. Effect of Temperature Change on Equilibrium: Decreasing Temperature
Decreasing the temperature of an exothermic reaction
causes the system to respond by shifting the reaction toward more heat.
shifts the reaction toward the products, increasing heat in system.
2SO2(g) + O2(g) SO3(g) + heat
Decrease Temperature

21. Effect of Temperature Change on Equilibrium: Increasing Temperature
Increasing the temperature of an exothermic reaction
causes the system to respond by shifting the reaction toward removing heat.
shifts the reaction toward the reactants, decreasing heat in system.
2SO2(g) + O2(g) SO3(g) + heat
Increase Temperature

22. Effects of Changing Conditions on Equilibrium

23. Study Check Indicate the shift in equilibrium of each change.
2NO2(g) + heat NO(g) + O2(g)
1) toward products 2) toward reactants
adding more NO
decreasing the temperature
removing some O2
increasing the volume
removing some NO

24. Study Check Indicate the shift in equilibrium of each change.
2NO2(g) + heat NO(g) + O2(g)
1) toward products 2) toward reactants
adding more NO 2) toward reactants
decreasing the temperature 2) toward reactants
removing some O2 1) toward products
increasing the volume 1) toward products
removing some NO 1) toward products

25. Concept Map