chemical kinetics

ΔG

determines whether a reaction is spontaneous or nonspontaneous

(-) = spontaneous

(+) = nonspontaneous

collision theory

rate of a reaction is proportional to the number of collisions per second between the reacting molecules

activation energy

minimum energy of collision necessary for a reaction to take place

Arrhenius equation

k = Ae^{-E_A / RT}

k = rate constant

A = frequency factor

E_A = activation energy

R = ideal gas constant

T = temperature in kelvin

ΔG_rxn

difference between the free energy of the products and the reactants

(+) ΔG = endergonic

(-) ΔG = exergonic

factors affecting reaction rate

• ↑ reactant concentration = ↑ # of effective collisions per unit time = ↑ reaction rate

• ↑ Temperature = ↑ reaction rate

• medium in which reaction takes place

• catalysts ↑ reaction rate without being consumed in the reaction

0 order reaction

rate of formation of product C is independent of changes in concentration of any of the reactants A and B

rate = k

k = rate constant

• units of M/s

Plotting 0 concentration vs time

• linear graph

1st Order Reaction

rate is directly proportional to only one constant

rate = k[A] or k[B]

k has units s^-1

concentration of radioactive substance A at any time t can be expressed as:

• [A]_t = [A]₀e^-kt

Plotting concentration vs. time

• nonlinear graph

2nd order reaction

rate is proportional to either the concentrations of two reactants or to the square of one of the reactants

rate = k[A][B] or k[A]² or k[B]²

k has units M^-1s^-1

Plotting concentration vs time

• results in a nonlinear curve

• 1/[A] vs time results in a linear curve

  • slope = k