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Collision Theory BIOB111 Session 4 (Factors affecting reaction rate #…
Collision Theory
BIOB111 Session 4
Collision Theory
Requirements
Activation Energy EA
the minimum amount of energy required for the chemical reaction to occur
Collision orientation
reactant molecules must be conveniently oriented when colliding so products can be formed
Molecular Collisions
reactant molecules must collide with one another to undergo a chemical change and form products
Effective collision
one that results in a chemical reaction
convenient orientation
of reactant molecules at the time of collision
#
energy of the collision ≥ activation energy
collision between molecules needs to have sufficient energy to break bonds within the reactants
energy of a collision depends on the speed of the reactant molecules and on the angle of their approach to hitting each other
Exothermic
reaction
type of exergonic reaction that releases energy in the form of heat
products contain less energy than the reactants
Endothermic
reaction
products contain more energy than the reactants
type of endergonic reaction that absorbs energy in the form of heat
Reaction rate
Reaction kinetics - study of the rate of chemical reaction
the rate at which reactants are consumed or products produced in a given time in a chemical reaction
two ways to measure
(1 is sufficient)
speed at which reactants(s) is/are used up
speed at which product(s) is/are formed
Energy
transfer
can't create or destroy energy, must be balanced within the reaction
breaking old bonds in reactants during a chemical reaction requires energy
forming new bonds in products releases energy
overall chemical reaction may either release or absorb energy
#
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Activation
energy
EA
the
minimum
combined kinetic energy that the colliding reactant molecules must possess so that their collision results in a chemical reaction
activation energy is inversely proportional to the rate of the chemical reaction
the lower the EA → the faster the reaction (more collisions exceed the EA)
the higher the EA → the slower the reaction
Transition state
- the bonds of the reactants are broken and the bonds of the products start forming
Exergonic
Reaction
#
release more energy than they absorb
the products have less potential (stored) energy than the reactants
energy released by bond formation > energy absorbed for bond breakage
Endergonic
Reaction
#
absorb more energy than they release
the products have more potential (stored) energy than the reactants
energy is absorbed from outside sources, so the reaction can occur
energy absorbed for bond breakage > energy released by bond formation
Factors affecting
reaction rate
#
Physical
nature of
reactants
reaction rate generally faster if reactants are in the same physical state
gas-gas interactions fastest (highest number of collisions)
includes physical state and the particle size of each reactant (solid - need to increase surface area)
Reactant
concentrations
increased concentration = increased reaction rate
less space between molecules leads to increased collisions
reaction rate directly proportional to the concentration of reactants
Reaction
Temperature
molecules move faster (more kinetic energy) and collide more frequently
higher energy between collisions (more likely to exceed activation energy)
increased temperature leads to increased reaction rate - directly proportional
temperature = regulation factor of chemical reactions
Presence of
Catalysts
more reactant collisions exceed lower activation energy requirements
increases the reaction rate
alternate reaction pathway that have lower initial activation energy
enzymes (proteins) are the catalysts within the human body
are not used in the reaction (can be reused)
Increased
pressure
only applies to reactions in the gaseous state
greater pressure = faster reaction rate
