1. It’s all about the …..
STRESS

2. Equations at Equilibrium
N2 + O2 + heat NO
Reactions that do not reach completion may stop at an equilibrium point.
That is to say that the amount of reactant becoming product is equal to the amount of product changing back into the reactant.

3. LeChatelier’s Principle
If we add stress we can force the amount of the reactants and products to change.
Changes happen to alleviate the stress.

4. What causes stress? Chemistry Class
Ok true but……LeChatelier was referring to different kinds of stress.

5. Changes in Temperature
What causes stress?
Addition of Chemicals
Changes in Pressure
Changes in Temperature

6. Addition of Chemicals Additional reactant—make more products
--shift to the right
Additional products—make more reactants
--shift to the left
Remove reactant or product—will shift to make more of what was removed

7. Addition of Chemicals

8. Addition of Chemicals Given the reaction: 2 KBr + I2(g) 2 KI + Br2(g)
If we added additional I2(g) to the system which direction would the equation shift?

9. Addition of Chemicals Given the reaction: 2 KBr + I2(g) 2 KI + Br2(g)
If we added additional I2(g) to the system which direction would the equation shift?
Answer:
Addition of I2(g) would allow more reactants to come together to form more products.
--shift right

10. Addition of Chemicals Practice:
For the following reaction: N2(g) + 3H2(g) NH3 (g)
Which direction would the reaction shift if more nitrogen gas was added?
2. For the following reaction: NH3(g) + HCl (g) NH4Cl (s)
Which direction would the reaction shift if more NH4Cl (s)
was added?
3. For the following reaction: CO2(g) +MgO(s) MgCO3(s)
Which direction would the reaction shift if more MgO(s) was added?

11. Addition of Chemicals Practice:
For the following reaction: N2(g) + 3H2(g) NH3 (g)
Which direction would the reaction shift if more nitrogen gas was added?
Shift toward the products (right)
2. For the following reaction: NH3(g) + HCl (g) NH4Cl (s)
Which direction would the reaction shift if more NH4Cl (s)
was added?
Shift toward the reactants (left)
3. For the following reaction: CO2(g) +MgO(s) MgCO3(s)
Which direction would the reaction shift if more MgO(s) was added?

12. Changes in Pressure
Changes in pressure can only effect systems in which gases are involved.
Increase Pressure: the equilibrium will shift towards the side of the reaction with the least number of moles of gas.
Decrease Pressure: the equilibrium will shift towards the side of the reaction with the higher number of moles of gas.

13. Changes in Pressure O2
H2O H2
H2O H2
3 moles = 67.2L
2 moles = 44.8L

14. Changes in Pressure O2
H2O H2
H2O H2
Increase in Pressure

15. Changes in Pressure Move towards side that had lower volume. Was 44.8L

16. Changes in Pressure For the reaction: N2(g) + 3Cl2(g) NCl3(g)
(22.4L L) (22.4L)
Which direction would the reaction shift if pressure was decreased?
Answer: The reaction would shift towards reactants. Remember an decrease in pressure will cause the reaction to shift toward the side with the higher number of moles of gas.
--shift left

17. Changes in Pressure Practice:
For the reaction: PCl3(g) + Cl2(g) PCl5(g)
What direction would the reaction shift if pressure was increased?
For the reaction: CO(g) + 2H2(g) CH3OH(g)
3. For the reaction: PCl3(g) + 3 NH3(g) P(NH2)3(g) + 3 HCl(g)
What direction would the reaction shift if pressure was decreased?

18. Changes in Pressure Practice:
For the reaction: PCl3(g) + Cl2(g) PCl5(g)
What direction would the reaction shift if pressure was increased?
The reaction will shift toward the products (right)
For the reaction: CO(g) + 2H2(g) CH3OH(g)
What direction would the reaction shift if pressure decreases?
The reaction will shift toward the reactants (left)
3. For the reaction: PCl3(g) + 3 NH3(g) P(NH2)3(g) + 3 HCl(g)
What direction would the reaction shift if pressure was decreased?
The reaction will remain the same, the volumes on both sides are equal.

19. Changes in Temperature
Before you can decide how temperature will effect the equilibrium, you must first identify if the equation is endothermic or exothermic.
Exothermic reaction: the reaction will shift towards the reactants (left)
Endothermic reaction: the reaction will shift towards the products (right)

20. Changes in Temperature
N2(g) + 3H2(g) 2NH3(g) + heat
Increasing the temperature of this
reaction will cause it to shift towards
the reactants.

21. Changes in Temperature
N2(g) + 3H2(g) 2NH3(g) + heat
Increasing the temperature of this
Reaction will cause it to shift towards
The reactants.

22. Changes in Temperature
CaCO3(s) + heat CaO(s) + CO2(g)
Reducing the temperature of this reaction
will cause it to shift towards the reactants.

23. Changes in Temperature
CaCO3(s) + heat CaO(s) + CO2(g)
Reducing the temperature of this reaction
Will cause it to shift towards the reactants.

24. Change in Temperature Practice:
For the reaction: SO3(g) + H2O(l) H2SO4(aq) + heat
In which direction would the reaction shift if temperature was increased?
2. For the reaction: N2(g) + O2(g) + heat NO(g)
In which direction would the reaction shift if the temperature was increased?
For the reaction: SO2(g) + O2(g) SO3(g) + heat
In which direction would the reaction shift if the temperature was decreased?

25. Change in Temperature Practice:
For the reaction: SO3(g) + H2O(l) H2SO4(aq) + heat
In which direction would the reaction shift if temperature was increased?
The reaction would shift towards the reactants (left)
2. For the reaction: N2(g) + O2(g) + heat NO(g)
In which direction would the reaction shift if the temperature was increased?
The reaction would shift towards the products (right)
For the reaction: SO2(g) + O2(g) SO3(g) + heat
In which direction would the reaction shift if the temperature was decreased?