Chemical Kinetics

Question 1

collision theory of chemical kinetics

Answer 1

• the rate of rxn is proportional to the number of collisions per second
• an effective collision occurs if molecules collide on the correct orientation and w sufficient energy to break existing bonds and form new ones (activation energy Ea)
• rate of rxn: rate = Z x f
  Z: total number of collisions occurring per second
  f: fraction of collisions that are effective
• Arrhenius equation: k = Ae^(-Ea/RT)
  k: rate constant
  A: frequency factor 1/s
  Ea: activation energy for rxn
  R: ideal has constant
  T: temp in Kelvin
• frequency factor inc collisions inc concentration

Question 2

transition state theory

Answer 2

• transition state has greater energy than both the reactants and products
• once activated complex is formed, it can either dissociate into the products or form reactants without any additional energy input
• transition states are diff from rxn intermediates in that they are theoretical constructs at max energy point rather than distinct identities with finite lifetimes
• transition state at the peak of the energy diagram

+deltaG endergonic

-deltaG exergonic

Question 3

temp and rxn rate

Answer 3

increases rxn rate bc inc in average chemical energy

Question 4

catalysts

Answer 4

• catalysts inc rxn rate w/o being consumed
• interact w reactants either by absorption or through intermediate formation and stabilize them to reduce Ea
• return to original chem states after product formation
• may inc frequency of collisions between reactants
• may change orientations
• may donate e- density to reactants

Question 5

homogenous catalysis

Answer 5

the catalyst is in the same phase as reactants

Question 6

heterogenous catalysts

Answer 6

diff phase as reactants

Question 7

rate

Answer 7

aA + bB ~> cC
(-delta[A]/a•deltat) = (-delta[B]/b•deltat) = (delta[C]/c•deltat)

Question 8

the coefficients x, y, etc representing the order of the reactants is determined how?

Answer 8

experimentally

no correlation with the coefficients

Question 9

for a reversible reaction, the Keq is equal to…

Answer 9

the ratio of the rate constant for the forward reaction, k, divided by the rate constant for the reverse reaction, k-1

Question 10

determining rate law exponents

Answer 10

aA + bB ~> cC

if doubling [B] results in a quadrupling of the rate of C formation, then the order of B is 2.

2^x = 4
x = 2

Question 11

to determine overall order of a reaction…

Answer 11

add all of the orders.

Question 12

radioactive decay formula

Answer 12

[A]t = [A]0e^(-kt)

Question 13

mixed order rxn can mean either…

Answer 13

noninteger order

OR

rxns that change over time

ex; rate = k1[C][A^2]/(k2 + k3[A])
C: catalyst