AP Chem Unit 7- Kinetics

collision theory

• chemical reactions occur when reactants collide w/ sufficient energy & right orientation

• breaks reactant bonds & forms new product bonds

• reaction rate depends on frequency of effective collisions (more collisions=more products)

true/false: any factor increasing number of effective collisions will usually increase reaction rate

true

catalyst effects on reaction rates

not consumed in process (can be recovered at end)

• decrease activation energy needed to occur

• adjust orientation of reactants

• only changes peak of energy/enthalpy graph

  • deltaH remains the same

concentration/pressure effects on reaction rates

• direct relation

• greater concentration leads to more collisions & likelihood of successful collisions

• higher pressure leads to faster reactions

physical state of matter effects on reaction rates

• gases/liquids (aq) react faster than solids

  • greater KE=more (successful) collisions

• solids have slow reaction rates

  • breaking into smaller pieces increases total surface area & more possible places for collisions to occur

  • more surface area=faster reaction rate

temperature effects on reaction rates

• greater temp=greater KE=greater rate of reaction

• particles are more likely to collide

• faster moving particles have higher probability of fulfilling activation energy

true/false: reaction rate is constant

false

the ___ rate is generally referred to in kinetics

instantaneous

rate law

• rate=k[A]^m[B]ⁿ

• exponents determined experimentally

  • determine effects of concentration

  • positive whole numbers- speed up reaction

  • negative- slow down reaction (rare)

• always in terms of reactants

zero order

rate of reaction does not change based on reactant concentrations

first order

rate is directly proportional to reactant’s concentration (concentration x2=rate x2)

second order

rate is exponentially proportional to reactant’s concentration (concentration x2=rate x4 or 2²)

zero order k unit

M/s

first order k unit

1/s

second order k unit

1/Ms

differential rate laws

express how rate of reaction depends on concentration of reactants

integrated rate laws

express how concentrations depend on time

integrated rate laws- zero order graphical analysis of a straight line

[A] vs. t; rate=k; k=-slope of line

integrated rate laws- first order graphical analysis of a straight line

ln[A] vs. t; rate=k[A]; k=-slope of line

integrated rate laws- second order graphical analysis of a straight line

1/[A] vs. t; rate=k[A]²; k=slope of line

true/false: rate constants are always positive

true

zero order integrated rate law

[A]₀ - [A]_t = kt

first order integrated rate law

ln[A]_t - ln[A]₀ = -kt

second order integrated rate law

1/[A]_t - 1/[A]₀ = kt

when asked to find initial rate of disappearance/appearance use:

mole ratios/stoichiometry