1. Rate of chemical change
Rate of chemical change is expressed in terms of
D Concentration of reactants or products

2. Collision Theory Reaction Rate depends on:
1) The number of collision per unit time between the reacting species.
2) The fraction of these collisions that are successful in producing a new molecule.

3. Activation energy
The reactants must gain enough energy to climb an energy hill
They form an activated complex or a “transition” state before they cascade down becoming products

4. Will a Reaction take place
Will a Reaction take place? Only if the collisions have enough energy, and have the right orientation
<= YES !!
NO =>

6. Concentration & Reaction Rate
The more concentrated the solution, the more chance of a collision
The more collisions, the more likely an “activated complex” will form
Click on picture to see movie

7. Particle size: small particle size increases collisions
Large amounts of surface area
Small amounts of surface area
Movie
Movie

8. The effect of temperature on rate
A high temperature means particles will collide more often
A high temperature means particles collide with more force

9. Effect of a catalyst
A catalyst provides an alternative route for the reaction with a lower activation energy

10. Effect of a Catalyst

11. Reversable Reactions and Keq
aA + bB  cC + dD
Keq = equilibrium constant
Keq = [productC]c[productD]d [reactantA]a[reactantB]b
Keq changes only when the temperature changes.

12. Reversible reactions reach a state of dynamic equilibrium
N2 + 3H2 2 NH3
Keq = [NH 3]2
[H2]3 [ N2]

13. LeChatelier’s principle
A system at equilibrium resists change. If it is exposed to stress (change) it will shift the equilibrium point to try to reduce the stress (change)
[Co(H2O)6]+2 + 4Cl- <==> [CoCl4]-2 + 6H2O
Pink blue

14. LeChatelier’s principle
If you add a reactant – the equilibrium shifts toward the product
If you add a product – the equilibrium shifts toward the reactant
If you take away a reactant – the equilibrium shifts toward the reactants
If you take away a product – the equilibrium shifts toward the product side

15. LeChatelier’s principle & heat
If the reaction is exothermic (heat is a product), So, adding heat shifts the reaction to the reactant side
If the reaction is endothermic (heat is a reactant) – adding heat shifts the reaction to the product side

16. LeChatelier’s principle & Pressure
If the reaction contains gas particles, pressure is considered a “stress” condition
2SO2 + O2  2SO3
Adding pressure shift the equilibrium to the side with fewer gas particles will have less pressure

17. Entropy: chaos The universe favors chaos Parts of a whole DS = Sp-Sr
Unmix
Unexplode
unmelt
DS = Sp-Sr
If DS is + , entropy change is favored

18. Is the reaction “spontaneous”
This is a “tug of war” between entropy and enthalpy
DG = DH - T DS (T is in kelvin)
If Gibbs free energy is a negative number, the reaction is spontaneous
If Enthalpy is negative, (exothermic), and entropy is + (chaos favored) the reaction is always spontaneous
If one of the conditions is not favored – it becomes a tug of war