1. Rates of Reaction
Unit 8

2. Reaction Times Time of reaction varies
Examples:
HCl + NaOH  NaCl + H2O Instantaneous
2 CO + O2  2CO2 Thousands of Years
It is therefore important to not only know if a reaction will occur, but also what the reaction rate is

3. Collision Theory Collision Theory: Concentration is very important
Atoms, ions, and molecules can react to form products when they collide, provided that particles have enough kinetic energy.
Concentration is very important
If the individual particles that collide do not have enough KE, they will bounce apart when they collide.

4. Collision Theory
Activation energy – the minimum amount of energy particles need in order to react
Activated complex – the temporary arrangement of atoms at peak of activation-energy barrier
Called the transition state – can re-form reactants or form products

5. Collision Theory

6. Kinetics vs. Thermodynamics
Kinetics – How FAST a reaction will occur
Thermodynamics – WHETHER a reaction will occur in the first place

7. Factors Affecting Reaction Rates
Temperature
Concentration
Particle Size
Catalysts
Pressure

8. Temperature Temperature = Kinetic Energy
By increasing the temperature of a reaction, the kinetic energy is increased
More particles have enough energy to collide at higher temperature (above activation-energy barrier)

9. Concentration Number of particles in a given area
Related to pressure (gas)
Increase collision frequency

10. Particle Size Smaller particles have larger surface area
Increased surface area means more reactant exposed for reaction
Ways to increase surface area:
Dissolve solid reactants to increase surface area
Grind into powder

11. Catalyst
Catalyst – substance that increases rate of reaction without being used up itself during the reaction
Lowers activation energy

12. Catalyst