Chemical Kinetics &
Collision Theory
Honors Chemistry
Unit 16
Daily 1 Lecture
Then and Now…
Previous Unit: Will a reaction occur?
Current Unit: How fast does a reaction occur?
Key Questions
1. How do you measure the speed, or rate, of a
reaction?
vs.
2. What factors influence how fast a reaction occurs?
Key Question #1
What is Rate?
• How fast something takes place
• Speed = distance/time
If a car travels 30 miles in ½ hour, what is it’s speed?
A Tale of Two Cars
Distance Traveled (miles)
70
60
50
40
30
Car 1
20
Car 2
10
0
0
20
40
Time (minutes)
60
80
Reaction Rates
• A measure of how fast a reaction occurs, or how
something changes during a given time period.
• How can you measure the speed of the following
reaction:
C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(g)
…measure how quickly the mass of solid glucose
decreases
…measure how quickly the gases (CO2(g) & H2O(g)) form
Reaction Rates (cont.)
Volume of Hydrogen Formed
(mL)
Mg(s) + 2HCl(aq)  H2(g) + MgCl2(aq)
60
50
40
30
20
10
0
0
5
10
Time (min)
15
20
Reaction Rates (cont.)
• Other possible things that could be measured,
depending on the reaction:
o
o
o
o
o
o
o
change in pressure as gases are formed or used up
change in volume as gases are formed or used up
change in mass as solid is formed or used up
change in temperature
change in conductivity
change in pH
change in color
ex) AgNO3(aq) + Cu(s)  CuNO3(aq) + Ag(s)
reaction rate = amount of product formed
time interval
product
In a Nutshell…
time
reaction rate = amount of reactant used
time interval
Or…
reaction rate = change in concentration
time interval
reactant
Or…
time
Key Question #2
What Affects Rates?
Collision Theory:
• Particles must collide for reactions to occur
• Rate depends on the frequency of collisions
TO SUCCEED, collisions must have:
• Sufficient energy
• Proper orientation
Increasing Chances for
Successful Collisions
• Temperature
• Concentration
• Surface Area
• Catalysts
• Nature of Reactants