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Collision TheoryAim: To identify the conditions necessary for a chemical reaction to occur.
Review Book Topic 8Text book Chapter 17
Unit 11: Kinetics and Equilibrium
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Collision Theory
Collisions between particles do not always result in a chemical reaction.
A reaction will only occur if there is an effective collision between molecules.
To have an effective collision:1) The reactant particles MUST hit with sufficient energy2) The reactant particles MUST have proper orientation. (Think lock and key model for enzymes)
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Reaction Rate
Aim: What factors affect the rate of a chemical reaction?
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What is kinetics?
Kinetics deals with the speed of chemical reactions.
Reaction Rate: the amount of time it takes for a chemical reaction to occur
Reaction rate is increased by an increase in the amount of effective collisions.
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1) Nature of the Reactants2) Concentration3) Surface Area4) Temperature5) Pressure (only affects gases)
What factors play a role in the speed of a reaction?
6) Addition of a Catalyst
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Nature of the Reactants
Certain substances are more reactive than others based on their chemical properties.
Example: Lithium is more reactive than Gold.
The more bonds that need to be broken the slower the reaction rate will be.
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Concentration
Increasing the concentration of the reactants will result in more collisions because there are more particles.
More collisions= a faster reaction rate (shorter time)
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Surface Area
Increasing the surface area of a reactant increases the number of sites where a collision can take place
Greater surface area = more collisions= faster reaction rate (shorter time)
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Temperature
Increasing temperature causes an increase in the average kinetic energy of molecules.
Higher kinetic energy means the particles move faster
This results in more collisions and a faster reaction rate.
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Pressure
A change in pressure only affects gases!
Increase pressure by decreasing the volume.
Less space between particles results in more collisions.
More collisions gives a faster reaction rate.
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Catalyst
Catalyst: a substance that speeds up a reaction but IS NOT A PART of the reaction.
The catalyst lowers the activation energy. (Less energy needed for an effective collision)
(Ex- Lighter fluid to light charcoals on a barbecue.)
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In short....
Increasing temperature = ________________________
Increasing concentration = ________________________
Increasing pressure = ____________________________
Increasing surface area = _________________________
Addition of a catalyst = __________________________