1. 9.1 Chemical Equilibrium Objectives S1:a-e; S2
Section 1 - chemistry

2. Essential Questions What is a reversible reaction?
What is a chemical equilibrium?
How does a reaction(s) come to equilibrium?
What does Le Chatelier’s Principle say?
What are ways to affect chemical equilibrium?

3. Reversible Reactions What is a reversible reaction? Example p 552:
A reaction that can go backwards so that products are reforming as reactants.
Example p 552:
Forward reaction NO2 (g) → N2O4 (g)
Reverse Reaction N2O4 (g) → 2 NO2 (g)
Write reversible RXN using a double headed arrow.

4. Reversible Reactions (cont)

5. SO3 decomposes to SO2 and O2
18.2
Reversible Reactions
SO3 decomposes to SO2 and O2
SO2 and O2
react to give SO3
At equilibrium, all three types of molecules are present.
Molecules of SO2 and O2 react to give SO3 . Molecules of SO3 decompose to give SO2 and O2 . At equilibrium, all three types of molecules are present in the mixture.

6. Chemical Equilibrium What is a chemical equilibrium?
Rate of forward reaction equals rate of reverse reaction
What happens to the concentration (how much you have) of the products and reactants?
Concentration of reactants and products stay constant because they are being formed as soon as they are being consumed

7. Chemical Equilibrium
Any system involving a reversible reaction will reach equilibrium if left alone
Called a dynamic equilibrium because its always active

8. Graphing equilibrium Concentrations
What happens to the concentration of the reactants at first?
Decreases
What happens to the concentration of products at first?
Increases
What happens to both as time passes?
They do not change
Are the concentrations in all equal in equilibrium?

9. Graphing Equilibrium Rates
What happens to the rate of the forward reaction at first?
Decreases
How about the Reverse reaction?
Increases
What happens to both as time passes?
They become equal to each other
How does a concentration graph compare to a rate graph?

10. Le Chatelier’s Principle
How does a see-saw work?
Weight be placed on one end causes the see-saw to move as it tries to get balanced
How do you think that principle applies to a chemical equilibrium?
When there is a change in conditions, the chemical equilibrium will shift
Like a see-saw, the equilibrium will shift to maintain balance

11. Le Chatelier’s Principle (cont)
Le Chatelier’s Principle states that when conditions of a chemical equilibrium are changed the equilibrium will shift towards the direction that will reduce that change
The 3 conditions that affect equilibrium are concentration of reactants/products, pressure, or temperature
Adding a catalyst affects each reaction equally and no overall impact

12. Changes in Concentration
When you add concentration the reaction shifts to the opposite side
When you remove the reaction shifts to the same side
What will happen if NO2 is added?
What will happen if N2O4 is added?
What will happen if N2O4 is taken away?

13. Changes in Pressure
For gasses if you increase pressure then volume decreases causing the equilibrium to shift to side with fewest number of gas molecules so they will take up less space
N2 (g) + 3H2 (g) ↔ 2NH3 (g)
If I wanted more ammonia should I increase or decrease the pressure?

14. Changes in Temperature
Depends on if reaction is Endothermic or Exothermic
Treat heat term as a reactant (left side) for endothermic and as product (right side) for exothermic

15. Changes in Temperature
Example: H2 (g) + I2 (g) ↔ 2 HI (g) + heat
What will happen if you increase the temperature?
If I wanted more HI, what would you change?

16. Changes in Temperature (cont)
For endothermic reaction which direction will the equilibrium shift if heat is added?
To the right (products)
How about for an exothermic reaction?
To the left (reactants)
How would removing heat affect an exo?
How about endo?

17. Essential Questions What is a reversible reaction?
What is a chemical equilibrium?
How does a reaction(s) come to equilibrium?
What does Le Chatelier’s Principle say?
What are ways to affect chemical equilibrium?

18. 9.1 Tracked Assignment
worksheet