kinetics

Question 1

the gradient of a concentration vs time curve at point t gives…

Answer 1

the rate of reaction at time t.

Question 2

rate is always…

Answer 2

positive

Question 3

the rate law can only be …

Answer 3

determined experimentally.

Question 4

the differential rate law tells us…

Answer 4

the rate of the reaction at a particular instant

Question 5

the integrated rate law is an expression that gives us…

Answer 5

the concentration of a species as a function of time. They can be used to establish the order of a reaction and then the rate constant.

Question 6

integrated rate law for zeroth order reaction

• on equation sheet

Answer 6

[A] = [A]0 -kt

Question 7

integrated rate law for first order reaction

• on equation sheet

Answer 7

Exponential graph :
[A] = [A]0 e^-kt

and

straight line graph
ln[A]t = ln[A]0 - kt

where k is the gradient.

Question 8

integrated rate law for second order reaction

• on equation sheet

Answer 8

exponential graph:
[A]t = [A]0 - kt

straight line graph :
1/[A] = 1/[A]0 + kt

Question 9

what is the definition of half life

Answer 9

the time taken for the concentration of the species to fall to half its initial value

Question 10

at equilibrium the rate of forwards and backwards reactions are ….

Answer 10

equal

Question 11

equation for rate at equilibrium

Answer 11

[B]eq / [A]eq = k1/ k-1 = K

Question 12

for first order reactions the ln[A] against t should be…

Answer 12

a straight line (linear)

Question 13

what does the 0 mean in [A]0

Answer 13

the initial concentration

Question 14

what shape is the graph of lnk vs t

Answer 14

linear

Question 15

what equation does the graph of lnk vs 1/t represent

Answer 15

the Arrhenius equation

Question 16

what is the Arrhenius equation

• on equation sheet

Answer 16

k = A e (-Ea / RT)

T = absolute temperature (K)
R = gas constant (8.314 J mol-1 K-1)
A = pre-exponential factor, a constant. (measure of the frequency of collisions.)

Question 17

what is the y-intercept of the lnk vs 1/t graph

Answer 17

lnA (pre-exponensial factor)

Question 18

what is a homogeneous catalyst

Answer 18

same phase as the reactants and products

Question 19

what is a heterogeneous catalyst

Answer 19

different phase as the reactants and products

Question 20

what is a pseudo first order reaction ?

Answer 20

elementary reaction which has more than one reactant, which concentrations both change during the reaction

Question 21

what is the method used to solve pseudo first order reactions

Answer 21

isolating one reactant at a time by having the other reactant in a large excess.

Question 22

if B is in large excess how can we rewrite k’

Answer 22

k[B]0

Question 23

what is k’

Answer 23

the effective rate constant for a fixed concentration of B ([B]0)

Question 24

what can you use half live for ?

Answer 24

to decide wether or not the reaction is first order and to get a value for the rate constant, k

Question 25

what equation will help me find the order of reaction when I have a table of data

Answer 25

ln(r1/r2) = m x ln ([A]1/[A]2)