1. Chemical Kinetics (Reaction Rates)
Chemical Kinetics: the study of how fast or slow a reaction takes place

2. Chemical Reactions occur at different rates!
There are slow reactions like a copper roof oxidizing (turning green) over a period of several years.
When you have a lot of bonds to break the reaction will be slow.
Covalent bonds are hard to break.

3. There are fast reactions: which require the least number of bonds to be broken.
Fast reaction involve ions.
Precipitation reactions are also fast.
Pb2+ (aq) + 2I1- (aq) --> PbI2 (s)
Neutralization reactions are also fast.
H2SO4(aq) + 2 KOH (aq) --> 2H2O (l) + K2SO4 (s)

4. Rate of Chemical Reactions
The rate of a chemical reaction is a ratio of the amount of change in a substance to the amount of time required for that change to take place.
a Reactant b Product
rate = D [Reactant] = 1 D [Product] D means change
a Dt b Dt
Example: BaCl2 + Na2SO BaSO4 + 2NaCl
The rate is - 1 D[BaCl2] = -1 D[Na2SO4] = 1 D[BaSO4 ] = 1D[NaCl]
Dt Dt Dt Dt

5. Mathematical Expression of a Rate Law
Suppose you are asked to find the mathematical expression of the rate for the following reaction:
C3H8(g) + 5O2 (g) --> 3CO2 (g) + 4 H2O (g)
rate law= k [C3H8] x [O2] 5
k is the rate constant
*note that only the reactants are in the expression*

6. Reaction Process
Most chemical reactions take place in a series of steps called reaction mechanisms.
Example:
Step 1: Cr(CO)6 --> Cr(CO) 5 +CO slow
Step 2: Cr(CO)5 + NH3 --> Cr(CO)5NH3 fast
RxN : Cr(CO)6 + NH3 --> Cr(CO)5NH3 +CO
The slowest step determines the rate of the reaction. It is called the rate determining step.

7. Collision Theory and Activation Energy

8. The collision theory states that for a product to be made the reactants must collide with enough energy and with the right geometry.
If the molecules collide with enough energy, then the atoms will rearrange and form a new product.
This is called an effective collision.

9. REACTION PROFILE activated complex activation energy Ea reactants
products
energy
course of reaction

10. ACTIVATED COMPLEX: is the temporary, unstable arrangement of particles present at the highest point in a chemical reaction profile.
ACTIVATION ENERGY (Ea): is the minimum energy with which particles must collide in order for the collision to be effective (resulting in the formation of a NEW substance)

11. Combustion Reactions A combustion reaction is exothermic.
A combustion reaction is a reaction between a fuel and oxygen.
If there is hydrogen within the molecules of the fuel, then water will be produced
C8H18 + O what are the products?
2 C8H O CO H2O

12. Fire Triangle (review of sec 4)
You need 3 things for combustion:
a fuel (wood or propane)
an oxidizing agent (oxygen- 21% in air)
a certain temperature
If you are missing any of these components, the rate will be zero, the fire will stop.