Section 18.2 (part A) lecture for Honors & Prep Chemistry

1. Bellwork- collision theory
Explain, using collision theory, WHY the
following factors increase reaction rate.
a. Increase temperature
b. Increase surface area
c. Increase reactant concentrations
d. Add a catalyst

2. At chemical equilibrium, no change
occurs in the amounts of the
products and reactants.
At equilibrium the system is stable
H2O(s) ⇌ H2O(l) equilibrium at 0°C
Means the
process is at
equilibrium

3. A reversible reaction is one in
which the conversion of reactants
to products and the conversion of
products to reactants occur
simultaneously.
forward 2SO2 + O2 ⇌ 2SO3
reverse 2SO3 ⇌ 2SO2 + O2

4. 2SO2 + O2 ⇌ 2SO3
There are 6 mol SO2 and 3 mol O2 in
a closed container
As the reaction progresses, reactants form
products.
The forward reaction rate SLOWS as reactant
concentration decreases.
The reverse reaction rate INCREASES as
product concentration increases.

5. 2SO2 + O2 ⇌ 2SO3

6. 2SO2 + O2 ⇌ 2SO3

7. When the rates of the forward and
reverse reactions are equal, the
reaction has reached a state of
balance called chemical equilibrium.

8. At equilibrium the concentrations of all
“species” are constant.
Equilibrium position = the specific
concentrations of all species at
equilibrium, which can be calculated for
any reaction.

9. SO2 and O2 SO3
react to give decomposes
SO3 to SO2 and O2
At equilibrium,
all three types of molecules are present.

10. If the rate of the shoppers
going up the escalator
is equal to the rate of the
shoppers going down,
then the number of
shoppers on each floor
remains constant,
and there is an equilibrium.

11. In order to reach
equilibrium you need
A closed container
Stable temperature
Low activation energies

12. The equilibrium constant (Keq)
is a ratio of product
concentrations to reactant
concentrations at equilibrium.
For aA + bB  cC + dD
Coefficients
Keq = [C]c[D]d become
[A]a [B]b exponents!

13. A value of Keq greater than 1 means that
products are favored over reactants;
A value of Keq less than 1 means that
reactants are favored over products.
products
=K
reactants

14. 18.2 Section Quiz.
1. In a reaction at equilibrium, reactants
and products
a) decrease in concentration.
b) form at equal rates.
c) have equal concentrations.
d) have stopped reacting.