CHE 2C - Ch. 15 Kinetics

Instantaneous Rate of Change

is the tangent line of the curve

order of rxn

the sum of the exponents

• is the coefficients in reaction mechanisms

zero order slope

[C] vs t

first order

ln[C] vs. t

second order

1/[C] vs. t

whats is the k in the graph?

it is the slope

Collision theory

1. particles must collide directly for a rxn to occur

2. reactants must hit with high enough energy to create a bond formation

Collision Frequency

number of molecular collisions per time unit

• only a fraction of collisions result in a rxn

Activation energy

minimum energy required in the molecules for a rxn to ocur

• molecule is activated

Orientation

molecules must enter a collision at the correct orientation in space in order for arxn to occur

a. correct molecules must interact

b. precise angle of impact most occur

Transition State theory

• reactants first collide, they form partial bonds

• rxn can proceed forward or reserve in this state

• peak of activation on a plot

Effect of Temp

the higher the Ea, the stronger rate depends on temp

• determined by the arrhenius equation

Frequency Factor (A)

depends on the frequency of collisions and proper orientation

Rxn mechanism

a step by step description of a chemical rxn where each step is called the elementary step

Unimolecular

involves a change in a single molecule or ionic structure

Rate determining step (RDS)

is the slowest step

• has the highest Ea or has an intermediate

Bimolecular

involves the collision of two reactant molecules in the rate-determining step, resulting in an exchange of atoms between them.

Favorable T and K conditions

fast rxn with stable products

Catalyst

• create a new pathway for the rxn at a lower Ea to increase the rxn rate

• is not consumed

Inhibitors

decreased the rate of rxn

Michaelis Menten Kinetics

a model for enzyme kinetics

Low substrate concentration

first order

high substrate concentration

zero order

the ratio k/Km measures how effective an enzyme converts a substrate into a product