Ch. 5: Chemical Kinetics

Question 1

rate-determining step

Answer 1

the slowest step in a mechanism

the rate of the whole reaction is only as fast as the rate-determining step

Question 2

collision theory

Answer 2

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

Question 3

activation energy

Answer 3

“energy barrier”

• minimum energy of a collision necessary for a reaction to take place
• only a fraction of collisions will exhibit this energy

Question 4

equation for the rate of a reaction according to collision theory

Answer 4

rate = Z * f

total # of collisions per second * fraction of collisions that are effective

Question 5

transition state theory

Answer 5

when molecules collide with energy equal to or greater than the activation energy they form a theoretical transition state

Question 6

reaction coordinate

Answer 6

traces a reaction from reactants to products

Question 7

energy in the transition state

Answer 7

higher than products or reactants

Question 8

free energy change of the reaction

Answer 8

difference between free energy of products and free energy of reactants

Question 9

exergonic reaction

Answer 9

negative free energy change, energy is given off

Question 10

endergonic reaction

Answer 10

positive free energy change, energy is absorbed

Question 11

activation energy of the forward reaction

Answer 11

difference in free energy between transition state and reactants

Question 12

activation energy of the reverse reaction

Answer 12

difference in free energy between transition state and products

Question 13

increase in concentration has what effect on reaction rate

Answer 13

increase concentration –> increase collision rate –> increase reaction rate

Question 14

increase in temperature has what effect on reaction rate

Answer 14

increase in temperature –> increase in kinetic energy –> increase in reactants reaching activation energy –> increase in rate AT IDEAL TEMPERATURES

Question 15

units of rate

Answer 15

mol / L*s (mols per liter per second)
OR
M/ s (molarity per second)

Question 16

rate law

Answer 16

rate = k[A]^x[B]^y

Question 17

what does k represent in the rate law

Answer 17

reaction rate coefficient or rate constant

Question 18

what do x and y represent in the rate law

Answer 18

the orders of the reaction

Question 19

when are the stoichiometric coefficients usual to the orders of the reactants

Answer 19

on the reactant side of the rate determining step

Question 20

overall reaction order is equal to

Answer 20

x + y

Question 21

what is the rate law for a zero-order reaction

Answer 21

rate = k[A]0[B]0=k

Question 22

what is the rate of a zero-order reaction dependent on

Answer 22

rate is

• independent of changes in concentration of reactants
• equal to k

Question 23

what is the rate of a first-order reaction dependent on

Answer 23

rate is dependent on changes in concentration of only one reactant

Question 24

what is the rate law of a first-order reaction

Answer 24

rate = k[A]1 OR =k[B]1

Question 25

what is the rate of a second-order reaction dependent on

Answer 25

rate is dependent on changes

• in concentration of both reactants OR
• on the the square the concentration of one reaction

Question 26

what is the rate law of a second-order reaction

Answer 26

rate = k[A]1[B]1 
OR = k[A]2 OR = k[B]2

Question 27

why are high order reactions rare

Answer 27

high order reactions require three molecules (rather than one or two) colliding in correct orientation with sufficient energy

Question 28

what is unique about mixed-order/broken-order reactions

Answer 28

orders are integers or change throughout the reaction