1. Reactions and Equilibrium
In a forward reaction, the reactants collide to make products as the reactions continues towards the right side
In a reverse reaction, the products collide to make reactants as the reactions continues towards the left side

2. As the reaction goes to the right, the reactant concentration decreases causing the forward rate to decrease as there are fewer collisions between reactant particles.
As equilibrium is approached, the reverse rate increases because the concentration of products increases as there are more collisions between product particles.

3. At equilibrium, the forward rate is equal to the reverse rate
At equilibrium, the forward rate is equal to the reverse rate. The concentration of reactants and products are both constant (BUT NORMALLY NOT EQUAL TO EACH OTHER…)
When the forward rate is equal to the reverse rate, the reaction is said to be in dynamic equilibrium because particles are still colliding and reacting.

4. A System at Equilibrium
At equilibrium, concentrations (M, mol, P, etc.) of reactant and product both remain constant.
N2O4(g) NO2(g)

5. (forward & reverse rxns occur simultaneously)
Dynamic
Equilibrium:
(forward & reverse rxns occur simultaneously)
N2O4(g) NO2(g)
double arrow

6. Dynamic Equilibrium: N2O4(g) 2 NO2(g)
Initially, forward & reverse rxns occur at different rates.
(based on collisions, one slows down; other speeds up)
At equilibrium: Rateforward = Ratereverse
N2O4(g) NO2(g)
Ratef
Rater

7. At Equilibrium… N2O4(g) 2 NO2(g) …concentrations are ________
…forward and reverse rates are ________
constant
equal
N2O4(g) NO2(g)

8. H2O(l) ⇄ H2O(g) Phase Change Equilibrium Example:
evaporation in a closed container
H2O(l) ⇄ H2O(g)
Phase Change
Equilibrium

9. Rate of Crystallization
Saturated Solution Equilibrium
Rate of Solvation =
Rate of Crystallization
Example:
At the end of making rock candy
Animation:
total moles of dissolved NaCl remains constant
total moles of undissolved NaCl(solid) remains constant

10. Quick Quiz!
1) When a reaction has reached equilibrium, reactants and products …
A) have stopped reacting.
B) continue forming.
C) have equal concentrations.
D) decrease in concentration. 10

11. A B ⇄
Quick Quiz.
100
2) A reaction starts with 100 molecules of reactant and no product. As it approaches equilibrium, the forward rate will ________ and the reverse rate will ________.
A) remain constant , increase
B) decrease , remain constant
C) increase , decrease
D) decrease , increase 11

12. A B ⇄
Quick Quiz.
100
3) A reaction starts with 100 molecules of product and no reactant. At equilibrium, the amount of reactant A will be…
A) greater than B
B) less than B
C) equal to B
D) constant 12