1. Chemical Equilibrium

2. Reversible Reactions liquid + heat → vapor vapor + cooling → liquid
Products formed react to produce starting reactants
A + B → C + D Forward (right)
C + D → A + B Reverse (left)
Simultaneous

3. Reaction Rates Speed w/ which reaction proceeds Varies
Temperature
Concentration
Catalysts
Chemical kinetics

4. What’s going on?

5. Dynamic Equilibrium Chemical equilibrium Two or more systems
Oppose each other
(forward and reverse reaction)
Same time
Same rate
When rate of forward reaction = rate of reverse reaction…Dynamic Equilibrium is attained!

6. Equilibrium

7. Le Chatelier
If stress is applied to a system in equilibrium, the system will respond in such a way as to relieve that stress and restore equilibrium under a new set of conditions.

8. Le what??? If change is imposed on a system in equilibrium…
then the system will adjust to a new equilibrium…

9. How does this work? What will effect a chemical reaction? Pressure
Concentration
Temperature
Volume
Catalyst

10. Concentration and Equilibrium
Concentration effects equilibrium
Effect on reactants is determined by experiment
What happens if you increase the reactants of the following reaction?
H2(g) + I2(g) HI(g)
Increases the number of reactants available for collisions…
What happens to the rate of the reaction?
It increases
The system will establish a new equilibrium

11. H2(g) + I2(g) HI(g)
What happens if we increase the concentration of [H2]?
Rate to the right increases
Reactants are used faster than products are produced
HI is produced faster than it is used
Eventually, equilibrium is reached
[I2]decreases and [HI] increases

12. Equilibrium and Volume
If one or more of reactants are a gas and the reaction is closed, then you will see significant changes to equilibrium with change to volume
How?
If you decrease the volume of the gas, what effect does that have on the reaction?
Think about the Ideal Gas Law…what would it do the concentration of the gas?
Increase!

13. CaCO3 (s) 825°C CaO (s) + CO2(g)
Decrease the volume
The reverse reaction speeds up
Equilibrium shifts to the left
WHY?
Decreasing the volume of the container increases the concentration of the carbon dioxide
It’s the only gas!
What happens to pressure if you decrease volume? Think…
Pressure will increase. (Boyle’s Law and Ideal Gas Law)

14. If volume decreases, pressure increases
If a system is all gas; shift in reaction and equilibrium will be toward the side of the reaction that contains the least molecules
Why?
By shifting this way the system is trying to reduce the number of molecules and thus lower the pressure

15. Haber Process

16. Temperature and Equilibrium
Increase temperature; increase rate
Why?
KE increases (what is KE)
Forward and reverse increase
How will equilibrium shift?
Toward the side of the equation that absorbs the heat
Greater increase occurs
Exothermic reactions favor a left shift
Endothermic reactions favor a right shift

17. Catalyst on Equilibrium
Influence rate / affects speed
Not consumed during reaction
Lowers activation energy
DOES NOT SHIFT EQUILIBRIUM

18. Activation Energy Minimum energy needed for reaction to occur
No change to
Energy
Reactants
Products

21. Equilibrium Constants
Reversible reactions
Concentration of products and reactants is constant
@ equilibrium, rate of forward reaction = rate of reverse reaction
Why is this significant?
Equilibrium constant

22. Keq @ particular temperature For the general equation
aA + bB ⇄ cC + dD

23. Significant of Keq
Magnitude indicates extent the forward or reverse reaction takes place
If Keq > 1, the amount of product at equilibrium is greater than the amount of reactants
If Keq < 1, amount of reactants at equilibrium is greater than the amount of products
If Keq is large, the reaction will go forward to completion
If Keq is small, the reaction will go to the left