Rates

Question 1

what is rate of reaction ?

Answer 1

change in amount of product / reactant per time

Question 2

Name 5 ways of measuring rate of reaction

Answer 2

• measure gas volume formed
• measure loss of mass due to gas
• complimentary to measure colour change
• measure pH change
• time for cross to disappear

Question 3

how to find reaction rate on Conc-time graph

Answer 3

find gradient (tangent)

Question 4

what are clock reactions for ?

Answer 4

calculating initial rate of a reaction

Question 5

when 1st order …

Answer 5

rate increases proportionally to concentration

Question 6

when 0 order …

Answer 6

rate is not affected by concentration

Question 7

when 2nd order …

Answer 7

rate increases by a x^2 to concentration increase

Question 8

how do you find the overall order of a reaction ?

Answer 8

add all of the orders of the reactants

Question 9

what does [A] show ?

Answer 9

concentration of A

Question 10

in rates experiments, why have the other reactants in excess ?

Answer 10

so that their concentration won’t change much, so change in rate is only due to reactant you are investigating

Question 11

the bigger the rate constant (k) is …

Answer 11

the faster the reaction

Question 12

on a 1st order rate-conc graph, k =

Answer 12

the gradient (graph is linear)

Question 13

what is the half-life a reaction ?

Answer 13

time taken for half of the reactant to be used up

Question 14

describe the half life for 1st order reactions

Answer 14

each half life will be the same length

Question 15

what are the units for k from half life ?

Answer 15

s^-1

Question 16

what is the equation for finding k from half life ?

Answer 16

k = ln2 / time of half life

Question 17

what is the rate determining step ?

Answer 17

the slowest step in a multi-step reaction

Question 18

what is the overall rate of a reaction decided by ?

Answer 18

rate determining step

Question 19

what are the two rules for working out mechanism of chemical reaction from rate equation ?

Answer 19

• any reactant in rate equation affects the rate, so must be (or something derived from) in rate determining step
• if reactant isn’t in rate equation, then not in rate determining

Question 20

the order of a reactant shows …

Answer 20

the number of molecules of that in the rate determining step

Question 21

the rate constant will change at different …

Answer 21

temperatures

Question 22

what is A in the Arrhenius equation ?

Answer 22

the pre-exponential factor (a constant)

Question 23

what does R stand for in Arrhenius equation ?

Answer 23

gas constant (8.31)

Question 24

what are the units for temperature in Arrhenius equation ?

Answer 24

kelvin

Question 25

for the Arrhenius equation, how is k affected when activation energy increases ?

Answer 25

as Ea gets bigger, k gets smaller

Question 26

ln k =

Answer 26

-Ea/RT + ln A

Question 27

what is an Arrhenius plot ?

Answer 27

graph with ln k against 1/T

Question 28

for the Arrhenius plot, what is the gradient ?

Answer 28

-Ea/R

Question 29

for the Arrhenius plot, what is the y-intercept ?

Answer 29

A

Question 30

give an example of a catalyst in a reaction

Answer 30

iron is used in Haber process to make ammonia

Question 31

what is a heterogeneous catalyst ?

Answer 31

catalyst that is in a different phase from the reactants

Question 32

what is a homogeneous catalyst ?

Answer 32

catalyst in the same state as the reactants

Question 33

how to increase rate of reaction by changing heterogeneous catalyst ?

Answer 33

increase SA of catalyst as reaction occurs on surface of catalyst

Question 34

how does a homogeneous catalyst work ?

Answer 34

forms an intermediate species

Question 35

why is catalyst good for Haber process ?

Answer 35

temp would have to be very high without, so saves money and energy

Question 36

how is poly(ethene) different when made with/without a catalyst ?

Answer 36

more dense, more rigid and higher melting point when made with catalyst

Question 37

Give an example of homogeneous catalyst

Answer 37

Catalysis of Ozone breakdown

Question 38

Heterogeneous catalyst example

Answer 38

Catalytic converter

Question 39

Any proposed mechanism must be consistent with :

Answer 39

Overall rate equation (correct reactants in rate determining step)
Overall equation for reactant

Question 40

How collisions are there in a single two of a reaction ?

Answer 40

No more that 2 usually

Question 41

A in arrhenius is related to what ?

Answer 41

The number of collisions per second

Question 42

What is e^-Ea/RT related to ?

Answer 42

The proportion of collision which are successful