Kinetics

Factors Affecting Rate

state of reactants; temperature; concentration; use of catalyst

What does a change in the state of reactants affect?

Increase in surface area increases rate (smaller particle size = bigger surface area)

What does temperature affect?

Increases in temp increases rate

What does concentration affect?

Increase in concentration increases frequency of collisions

Collision Theory

Reactants must collide in the correct orientation and with sufficient energy to react

Change in number of collisions causes

reaction rate to change

Rate Law

Rate = k[A]ᵐ[B]ⁿ

Rate law is only written with

reactants

Zero order

[ ] over time

Slope of zero order

-k

First order

ln[ ] over time

Slope of first order

-k

Second order

1/[ ] over time

Slope of second order

+k

Half-life of first order reaction

remains constant

Successful collisions need

enough energy to overcome Eₐ & proper orientation to break bonds

Mechanisms

Rate law of any elementary reaction can be written from its stoichiometry

Overall rate law is determined by

the slowest step

Larger rate constants leads to

larger % of moles having successful collisions

Rate law formula includes

catalysts (element goes from reactant → product)

Enzymes

Type of catalyst

Rate law formula does not include

intermediates (element goes from product → reactant)

This energy profiles represents a reaction that is

exothermic; 2-step mechanism; slow 1st step

This energy profiles represents a reaction that is

endothermic; 2-step mechanism; slow 2nd step

This energy profiles represents a reaction that is

endothermic; 1-step mechanism

To find ΔH from bond rates

broken bonds — formed bonds

(reactants — products)

When ΔH is negative

reaction is exothermic

When ΔH is postive

reaction is endothermic