1. Rates of Reaction and Equilibrium

2. Rates Measurement of change that occurs within an interval of time
Collision Theory – Particles that contain enough kinetic energy will collide and stick together causing reactions
Activation energy – The minimum amount of energy particles must have to react

3. Activation Energy Activation NRG Reactants NRG released by rxn
Products

4. Things that affect rxn rates
Temperature – increasing temp. increases motion of particles
Concentration – cramming more particles in a fixed space increases the frequency of collision
Particle size – smaller size = larger surface area and more area to react
Catalyst – substance that increases rxn rate without being used up

5. Activation Energy w/ catalyst

6. A B Chemical Equilibrium
State in which the forward and reverse reactions take place at the same rate
A B 1%
99%

7. Le Châtelier’s Principle
If a stress is applied to a system in dynamic equilibrium, the system changes to relieve the stress.

8. Concentration
Changing the concentration will force the equilibrium to shift.
CO + 2 H2 ⇌ CH3OH
Adding more carbon monoxide will force an equilibrium shift towards the product

9. Temperature
Increasing the temp. causes equilibrium to shift in the direction that absorbs heat.
N2 + 3 H2 ⇌ 2 NH3 ΔH = −92kJ
This is an exothermic reaction when producing ammonia. If you lower the temperature, the equilibrium would shift in such a way as to produce heat. Since this reaction is exothermic to the right, it would favor the production of more ammonia

10. Pressure Changing pressure causes an equilibrium shift.
N2 + 3 H2 ⇌ 2 NH3 ΔH = −92kJ
An increase in pressure causes the reaction to shift to the side with the fewer moles

11. Equilibrium Constants
Keq
aA+bB cC + dD
Keq >1, products favored at equilibrium
Keq <1, reactants favored at equilibrium
[C]c [D]d
Keq =
[A]a [B]b

12. Spontaneous RXNs
Rxns that occur naturally and favor the formation of products.
All spontaneous rxns release “free energy”
Free Energy – energy that is available to do work. This energy is not 100% efficient, some energy is lost as friction and heat.
Nonspontaneous rxns – rxns that do not favor the formation of products

13. Entropy Measurement of disorder in a system.
The law of disorder – processes move in the direction of maximum disorder or randomness
The size and direction of heat changes and entropy changes together determine whether a rxn is spontaneous.

14. Entropy Tidbits
Entropy of a gas is greater than the entropy of the liquid or solid
Entropy increases when a substance is divided into parts (dissociation)
Entropy tends to increase in chemical reactions in which the product molecules out number the reactant molecules
Entropy tends to increase when temperature increases

15. Is Reaction Spontaneous?
Heat Change
Entropy
Spontaneous?
Decreases (Exo)
Increases
Yes
Increases(Endo)
Only if entropy is more favorable than Δ heat
Decreases
Only if Δ heat is more favorable than entropy No

16. Standard Entropy ΔS0 = S0 (products) – S0 (reactants) J/K • mol
The theoretical entropy of a crystal at 0K is 0
ΔS0 = S0 (products) – S0 (reactants)
J/K • mol

17. Gibbs free-energy change
ΔG = ΔH – TΔS
The maximum amount of energy that can be coupled to another process to do useful work.
ΔG is negative in spontaneous reactions