Collision Theory
1.
Matter is moving particles.
2.
Temperature increases- particles move faster
-more collisions
-more collision energy.
3.
Chemical reactions
-bonds break
-new bonds form
4.
Collisions provide the energy.
Collision Theory
• You need a collision between reactant particles
(molecules, atoms, or ions) to have a reaction.
• Collisions provide the energy required to break
bonds (in a reaction, atoms and electrons are
rearranged) and form new ones.
• Most collisions are not successful
Collision Theory
A successful collision requires:
1.
Favourable Geometry
products
2.
Poor Geometry
no products
Sufficient Energy to break the chemical bonds
Activation energy is
the minimum
amount of energy
required for a
successful collision.
The Collision Theory can be used to explain how the rate of a reaction can be changed.
Reaction rates can increase due to:
1.
More collisions
2.
Harder collisions- greater collision energy
3.
Lower activation energy or Ea- low energy collisions are more effective.
And that’s it!
The Collision Theory can be used to explain how the rate of a reaction can be changed.
1.
Increasing the temperature increases the rate because there are:
• More collisions
• Harder collisions
 Increase temperature is an increase in kinetic energy (KE)
2.
Increasing the reactant concentration increases the rate because there are:
• More frequent collisions
3.
Adding a catalyst
• Catalysts lower the activation energy or Ea - energy required for a successful
collision
Eg. If energy required for a particular rxn is 100 kJ/mol, a catalyst may reduce this to
say 75 kJ/mol
• lower energy collisions can be successful
Movie
4.
Changing the nature of the reactant for a more reactive chemical increases
the rate
• If a reactant has many bonds to be broken, it occurs slower than one which has
fewer bonds to be broken
✔
5Fe2+ + MnO4- + 8H+ ----------> 5Fe3+ + Mn+2 + 4H2O
5C2O42- + 2MnO4- + 16H+ ----------> 2Mn+2 + 8H2O + 10CO2 (g)
Which is faster?
5.
Increasing the surface area of a solid reactant increases the rate because:
• More frequent collisions
 Grinding or breaking down reactants to expose more surface
 Only applies to heterogeneous rxns (more than one phase)
 See page 8 Hebden
Video Clip: How to Speed Chemical
Reactions
Explain each Scenario Using the Collision Theory
1.
A balloon full of H2 and O2 do not react at room temperature.
Ea is too high for the room temperature collisions
A small spark ignites causes an explosion.
The spark provides the Ea and it explodes because it is exothermic
Explain each Scenario Using the Collision Theory
2.
A candle does not burn at room temperature
Ea is too high for the room temperature collisions
A match causes the candle to burn
The match provides the Ea
The candle continues to burn
It burns because it is exothermic
Explain each Scenario Using the Collision Theory
3.
H2O2 decomposes very slowly at room temperature.
2H2O2(aq) → O2(g) + 2H2O(l)
KI increases the reaction rate dramatically.
KI is a catalyst as it is not a reactant and it speeds up the rate.
Lowers the Ea- allows low energy collisions to be successful
Describe and Graph the Relationship between the Following
I. Ea and the Rate
• Decreasing the Ea increases the rate- inverse.
Rate
Ea
II. Temperature and the rate
• Increasing the temperature increases the rate- direct.
Rate
Temp
III. Concentration and the rate
• Increasing the concentration increases the rate- direct.
Rate
Conc
IV. Ea and the temperature
• The only way to change the Ea is by adding a catalyst!
No relationship!
Temp
Ea
Which factors increase the percentage of successful collisions?
I.Increasing temperature
II.Increasing concentration
III.Increasing surface area
IV. Adding a catalyst