5.1.1 kinetics

Question 1

give the equation for finding out k in a first order reaction

Answer 1

k=ln2/t1/2 (half-life) units are s^-1

Question 2

give the definition of rate of reaction

Answer 2

the change in concentration of a substance in unit time

Question 3

in a concentration vs time graph how can gradient be worked out

Answer 3

gradient=curve plot a tangent and use y/x to work it out

Question 4

how can the total order of a reaction be worked out

Answer 4

by adding all the individual orders together

Question 5

give the arrhenius equation

Answer 5

k=Ae- Ea/RT

Question 6

give another way that the arrhenius equation that is used

Answer 6

lnk=- Ea/R x 1/t + lnA aka y=mx+c

can also be used as lnk= -Ea/RT + lnA

Question 7

how can the gradient be worked out from the arrhenius equation

Answer 7

gradient = - Ea/R or Ea= gradient x r

Question 8

how can lnA be calculated from one data point

Answer 8

lnA=lnk - (gradient x 1/t)

A=e^lnA

Question 9

how do clock reactions work

Answer 9

a sudden colour change is observed when the products react with the indicator once it is no longer being used up

Question 9

what happens during a clock reaction

Answer 9

the change in concentration of reactants is very small over the time period of the reaction
temperature stays constant
at the end point the reaction has not proceeded too far

Question 9

give two reasons why it is unlikely a reaction can take place in one step

Answer 9

the rate equation doesn’t match the overall equation

collision is unlikely with more than two ions

Question 10

describe a method more efficient than continuous monitoring

Answer 10

• initial rate method where you time how long it takes for a set amount of product to form for different concentrations of reactant
• this means you wont have to monitor several experiments and graphs

Question 11

what is zero order

Answer 11

rate is unaffected by changes in concentration

Question 12

what is first order

Answer 12

rate doubles as concentration doubles

Question 13

second order

Answer 13

rate quadruples as concentration doubles

Question 14

explain the effect of temperature on k and rate

Answer 14

• k=Ae
• k is proportional to rate
• if temperature increases the k increases
• as k is proportional to rate this means rate also increases

Question 15

explain the effect of the use of a catalyst on k and rate

Answer 15

• a catalyst lowers Ea so k is increases

- k is proportional to rate so rate also increases

Question 16

what is a half-life

Answer 16

the time it takes for half of a reactant to be used up

Question 17

how can half lives indicate first order

Answer 17

if they are constant

Question 18

How can A be calculated from lnA

Answer 18

e^A

Question 19

give the equation for rate an rearrange to make k the subject

Answer 19

r=k[X]^n[Y]^m

k=rate/[X]^n[Y]^m

Question 20

what is the rate determining step and how does it affect the rate equation

Answer 20

• the slowest step in a reaction that the overall rate depends on
• any reactant that occurs in or before the rate determining step appears in the rate equation
• intermediates do not go into the rate equation but catalysts do