H Chem 11-12 Unit 6Collision Theory
slide 1
•Collision Theory is an explanation of the
mechanism by which reactants change to
products
•Chemical Reaction: the intramolecular &
intermolecular forces of atoms of reactants break
apart so atoms can rearrange into products
(forming new intra/intermolecular forces)
•2 Requirements for a reaction to occur:
•Collide with sufficient force to overcome
Activation Energy (energy to break
intra/inter)
•Collide with proper orientation
Collision Theory
slide 2
• “Effective Collision”
• a collision which results in product formation
•Must possess BOTH sufficient force and proper
orientation
•“Ineffective Collision”
• a collision which does not result in product
formation
•Lacks EITHER or BOTH sufficient force or proper
orientation
Reaction Rate slide 3
•The Rate of a Reaction is the speed in which a
reaction occurs (i.e. the speed in which a reactant
becomes product)
•Rate can be altered by manipulation of the two
requirements needed for an effective collision
•Force: change kinetic energy of moving particles
•Orientation:
•we cannot physically re-orient particles
• we can manipulate the frequency of collisions
and, therefore, increase the chance for more
collisions with proper orientation
Factors Affecting Reaction Rate slide 4
•4 Factors can be used to affect reaction rate
•You are responsible for
•WHAT is meant by the factor
•Describing HOW the factor affects particles and WHY this
factor can alter the rate of a reaction
•Which of the 2 requirements for an effective collision are
being manipulated and how so
•4 factors affecting reaction rate:
•Temperature
•Concentration & Pressure
•Surface Area (particle size)
•Catalysts
Factors Affecting Reaction Rate slide 5
Temperature:
http://www.yteach.co.uk/page.php/resources/view_all?id=reaction_rate_factor_collision_theory_temperature_concentration_reactant_
pressure_t&from=search
•WHAT:
•Measure of average KE (motion) of particles
•HOW/WHY:
•Increasing KE increases rate (direct)
•Particles are moving more quickly and will
collide with greater force as well as more often
•Manipulated Requirement(s) and HOW:
•Force—changing speed
•Orientation—increasing frequency of collision
Factors Affecting Reaction Rate slide 6
Concentration & Pressure:
http://www.yteach.co.uk/page.php/resources/view_all?id=reaction_rate_factor_collision_theory_temperature_concentration_reactant_
pressure_t&from=search
•WHAT:
•Concentration is a measure of number of particles in a given
volume
•Pressure (by changing size of volume) affects density of
particles
•HOW/WHY:
•Increasing concentration and/or pressure increases rate
(direct)
•Increasing concentration results in more particles in a given
volume, so more collisions
•Increasing pressure results in same number of particles in a
smaller volume, so more collisions
•Manipulated Requirement(s) and HOW:
•Orientation—increasing frequency of collision
Factors Affecting Reaction Rate slide 7
Surface Area (Particle size)
http://www.yteach.co.uk/page.php/resources/view_all?id=reaction_rate_factor_collision_theory_temperature_concentration_reactant_
pressure_t&from=search
•Surface Area:
•WHAT:
•Surface area (or “particle size”) refers to the amount of
reactant exposed to the othe reactant(s)
•HOW/WHY:
•By increasing surface area, the rate increases (direct)
•Surface area can be increased by separating a “clump”
of reactant so more particles of each reactant can mix
•Manipulated Requirement(s) and HOW:
•Orientation—increasing frequency of collision
Factors Affecting Reaction Rate slide 8
Catalysts
http://www.yteach.co.uk/page.php/resources/view_all?id=reaction_rate_factor_collision_theory_temperature_concentration_reactant_
pressure_t&from=search
•WHAT:
•Substance that do NOT act as reactants or products—a
catalyst is unchanged after the reaction
•HOW/WHY:
•Catalysts reduce the amount of energy needed for an
effective collision (reduce the required activation energy)
•Catalysts are chemicals which temporarily react with the
reactants then quickly ‘let go’
•Manipulated Requirement(s) and HOW:
•Force—the amount of required force is reduced
Collision Theory Practiceslide 9
1. Does every collision result in a chemical reaction? What is
an effective collision? What are the 2 requirements?
2. If one were to increase the frequency of collisions, which of
the two requirements is being manipulated and why?
3. Solid iron (Fe) can be used as a catalyst to create
ammonia, NH3, from N2(g) and H2(g). Will the iron used in
this reaction be available for future reactions? Explain.
4. After being snapped, one glow stick is put in the freezer
and another in a pre-heated oven.
a.
b.
c.
d.
e.
Which will produce light most quickly?
Which will stop producing light most quickly?
Which factor is being altered in this scenario?
Describe what is happening on a molecular level to the reactants
of each of the two glow sticks
How does changing this factor affect the requirements for an
effective collision?
Collision Theory Practiceslide 10
5. A series of demos related to Collision Theory &
Reaction Rates will be performed. Record the
chemical reaction occurring in each & explain
which factor(s) is being used to increase the
reaction rate and which requirement is being
manipulated and how.