Lecture 16 - Chemical Kinetics

Question 1

concept of rate:

Answer 1

within chemistry, the rate of a reaction is simply a measure of concentration as a function of time

Question 2

how can you calculate instantaneous rate?

Answer 2

you can calculate instantaneous rate through drawing a tangent to the curve

Question 3

what is meant when referring to a reactions ‘order’?

Answer 3

non-linear data that tells us that rate varies with concentration - nature of this variance gives reaction order

Question 4

reaction order:

Answer 4

The degree to which rate (gradient) varies with concentration changes depending on the order

Question 5

describe the components of the rate equation -
rate (v) = k [C1]^a[C2]^b:

Answer 5

k = rate constant

[C1] & [C2] = concentration of reactant

powers (a & b) = the order of each reactant

Question 6

what is the only way in which we can test out order:

Answer 6

we can only test it experimentally through testing out the order by using pseudo-first order conditions – put one reactant in large excess such that its
concentration is effectively constant

Question 7

if we do a pseudo test and where one reactant is in excess to give a graph with a linear upwards line of data points, what can we infer?

Answer 7

we can infer that this reactant is of a first order

Question 8

if we do a pseudo test and where one reactant is in excess to give a graph with a horizontal flat line of data points, what can we infer?

Answer 8

we can infer that the role that this reactant plays is zero order

Question 9

if we don’t change the initial concentrations but we can make the reaction go faster/slower, then what must we be able to do?

Answer 9

we must be able to vary the value for K

Question 10

define each symbol in the arrhenius equation -

k = Ae ^( - [Ea/RT] )

Answer 10

k - rate constant

A - pre-exponential factor / as for k

Ea - activation energy. / J mol^-1

R - gas constant / 8.314 K mol^-1

T - temperature / K

Question 11

the exponential dependence of k on Ea and T tells us:

Answer 11

(1) k decreases rapidly with increasing Ea

(2) k increases rapidly with increasing T

Question 12

calculating Ea from arrhenius equation:

Answer 12

you re-arrange the arrhenius equation to get you

ln k = ln A - (Ea / RT)

y = mx +c

WATCH YT VIDEO ON HOW TO DO

Question 13

pre-exponential factor:

Answer 13

the pre-exponential factor is essentially a measure of successful collisions

Question 14

FINISH

Question 15

Collision theory requires some assumptions, one of which is:

Answer 15

• molecules are structureless, hard spheres with no internal energy

Question 16

FINSH