Jon Gillespie
Evan Rosenfeld
Unit 15 – Kinetics:
Rates Of Chemical Reactions:
Rate= Change of some quantity / time
For example, Δ distance / time = velocity
Rate of reaction = -Δ[N2O] / Δ time
Reaction Conditions And Rate:
k = Ae(-Ea)/(RT)
Where A is the percent of properly aligned collisions, Ea is activation energy, T is temperature, and R is 8.314 JK-1 mol-
Concentration of Reactants
this is because the rate is proportional to the concentration of reactants, so as the reaction
proceeds and the reactants are used up, rate decreases
Temperature
T is proportional to KE which is proportional to velocity (squared). As T increases,
molecules have more frequent, more forceful collisions, speeding up the reaction rate
Catalysts
Catalysts provide an alternative path for reactions, one with much lower activation
energy. Therefore, catalysts speed up the rate of reaction. However, they speed up the
forward and reverse reactions equally, so there is no change in the k.
A Microscopic View of Reactions:
k = Ae(-Ea)/(RT)
Collision theory states two conditions that must be met for a collision to occur
The molecules must collide properly i.e. have the correct orientation
They must collide with sufficient energy i.e. Ea must be met
Writing Rate Equations:
Rate of a Reaction = K*[A]a[B]b
Where A and B are reactants of the reaction
And a and b are determined by analysis of experimental data
The Relationship Between Concentration and Time:
When concentration versus time is graphed k or the rate constant is equal to the slope
Linear slopes only result from certain variables that depend upon the order of the reaction
Mechanisms:
Reactions are composed of various elementary steps
The slowest elementary step is the rate determining step
Rate equations for elementary steps are based off stoichiometry
If the rate determining step has an intermediate, you must substitute to get it in terms of
the reactants