Reaction Rates

1
Reaction Rates

• Notes12
• Chapter 17

2
Reaction Processes Rates

• Reactions are written in simplified forms-showing
  reactants turning into products
• reactants ? products
• Real reactions are more complex
• Elevated energy states, and temporary substances
  (activated complex) are the rule
• Some reactions ? more complex? several distinct
  steps

3
Reaction Rates

• Chemical reaction rates vary widely
• Some reactions are completed within a few
  milliseconds
• Others require thousands of years
• Most Reactions start off relatively rapidly, slow
  steadily, and become very slow as they approach
  completion
• Some reactions simply stop at completion. Others
  level out at an equilibrium with their reverse
  reactions (forward reverse rates equal)

4
Reaction rate

• Average rate at which reactants produce products
• CO(g) NO2(g) ? CO2(g) NO(g)
• Reaction rate ?quantity
• ?time

Time (s) NO (M)
0.00s 0.00
2.00s .010
5
Pg. 531

• Practice problems 1,3

6
Collision Theory

• Explains chemical reactions in terms of effective
  collisions between particles.
• -sufficient energy
• -favorable orientation
• Conditions that favor effective collisions, favor
  reactions.
• Increasing Temperature ( pressure) increase the
  frequency energy of collisions favoring most
  reactions

7
Activation Energy, Activated Complexes

• Most physical chemical changes require an input
  of energy to breakdown older structures
• Bonds within reactants are broken down with a
  specific amount of energy called Activation
  Energy .
• Activation energy is amount of energy to
  activate the reaction, get it going
• energized, broken down reactants ? temporary
  activated complexes ? products

8
Activated Complexes

• ReactantsEnergy?Activated complex
• Internal Energy Peaks in this complex, then
  starts to drop as more stable products begin
  forming.
• Activated Complex ? Products Energy
• Draw 2 graphs

9
Reaction Rates (5 factors affecting rates)

• 1. Substances involved Reaction Type Ions in
  solution react very fast Most metals corrode
  slowly
• 2. Temperature Kinetic Energyhigher temp.
  speeds up most reactions
• 3. Concentration reactions go faster at higher
  concentrations (more effective collisions)

10
Reaction Rates (5 factors affecting
rates)Continued

• 4. Contact Area (surface area, mixing)fine
  powder, versus large pellets into liquid
• 5. Catalysts-substances that promote or speed up
  reactions without themselves being consumed.
  Catalysts lower activation energy. Enzymes are a
  type of catalyst