1. Reaction Rates & Equilibrium
Rates of Reaction

2. Collision Theory
Rate: measure of speed of any change that occurs within an interval of time
Expressed in amount of reactant changing per unit time
Collision Theory: atoms, ions, and molecules can react forming product when they collide
Must have enough kinetic energy or they bounce apart unchanged

3. Chemical Reaction
Activation Energy: the minimum energy that colliding particles need to react
Activated Complex: unstable arrangement of atoms that forms momentarily at the peak of activation-energy barrier.
Lifetime: 10-13s
Transition state

4. Factors Affecting Ration Rate
Temperature
Hi temp  >KE more collisions inc. rxn. rate
Concentration
[Hi]  more collision  inc. rxn. rate
Particle Size
Smaller particle size  greater surface area
Greater surface area, increase exposure to collision, and inc. rxn. rate
Catalyst: increases a reaction without being changed
Inhibitor: interferes with a catalyst
Reaction slows or even stops

7. Reversible Reactions and Equilibrium

8. Reversible Reaction
Reaction in which the conversion from reactant to products and products to reactants happens simultaneously
2SO2 + O2 ↔ 2SO3
Chemical Equilibrium: when the forward and reverse rates are equal
Reactions, fwd. & rev., still occur
No net change in concentration

9. Catalyst: speeds up the fwd. and rev. reactions equally
Irreversible reactions: one set of components is completely converted to a new substance
Catalyst: speeds up the fwd. and rev. reactions equally
Don’t effect equilibrium concentrations

10. LE CHÂTELIER’S PRINCIPLE
When stress is applied to a system, the system will responds to relieve the stress
Shift equilibrium position
Stresses:
Concentration
Temperature
Pressure

11. LE CHÂTELIER’S PRINCIPLE
Concentration
H2CO3 ↔ CO2 + H2O
Add CO2
Shifts left
Remove CO2
Shifts right
Add H2O

12. Affects of Temperature
Increasing the temp.  shift in the direction that absorbs heat
2SO2 + O2  2SO3 + heat
Add heat
Shifts left
Cool Rxn.
Shifts right

13. Affects of Pressure
Pressure changes affect gaseous systems that have unequal # of moles of reactants and products
Want to optimize room
N2(g) + 3H2 (g)  2NH3(g)
Increase pressure
Shifts right
Decrease pressure
Shifts left

14. Equilibrium Constant
Keq: ratio of product concentration to reactant concentration at equilibrium
raised to the power = # of moles
Only the concentration of gases and substances in solution are shown
Concentration for pure liquids and solids are not shown

15. Equilibrium Constant aA + bB  cC + dD Keq >1: favors products
Keq <1: favors reactants

16. Example Problems
A liter of gas mixture at equilibrium contains mol of N2O4 and 0.030mol of NO2. Write the Keq expression and determine its value.
N2O4  2NO2

17. Calculating an Equilibrium Constant
HI placed in a sealed container and comes to equilibrium; equilibrium reaction is:
2HI(g) H2(g) + I2(g)
Equilibrium concentrations:
[HI] = 0.54 M
[H2] = 1.72 M
[I2] = M
Substitute concentrations:
Keq = [H2] [I2]
[HI]2
Keq= [1.72] [1.72] = 2.96
[0.54]
= or 1.0 x 101
2 significant figures