Kinetics II PPQs

Question 1

How to work out order wrt something using table with
Initial concentrations and
Initial rates

Answer 1

To work out order of ax look at experiments where X is CHANGING and others are constant

Question 2

What do the tables usually show if ur comparing experiments to work out orders

Answer 2

Experiment number
Initial concentrations
Initial rates

Question 3

What measurements do u record in the table when doing clock experiments?

Answer 3

Temperature (Kelvin)
1/temperature (Kelvin ^-1)
Rate constant (dm^3 mol^-1 s^-1)
ln k (log for rate constant)

Question 4

How would u plot a graph from a clock reaction if u wanted to find Ea?

Answer 4

ln k (y axis)

1/temperature in Kelvin (x axis)

Question 5

How would u find the Ea from a

ln k
1/T graph

?

Answer 5

Gradient (large as possible)

Ea = gradient x (8.31/1000)

Question 6

When calculating Ea from a ln graph what to remember to check about the line?

Answer 6

If line is negative then set 
gradient x (8.31/1000) = -ve Ea rather than +ve sea

Question 7

State why the order of reaction with respect to iodide ions cannot be five even though five mols of iodide ions are shown in the equation (1)

Answer 7

Chance of five or more ions colliding in the rate determining step is negligible

Question 8

State where are the total volume should be kept the same in a clock reaction (1)

Answer 8

So the volume of iodate (V) ions is proportional to concentration

Question 9

Justify why a graph might be showing sm is first order

Answer 9

Straight line goes through origin

Rate is proportional to concentration

Question 10

Explain the purpose of the starch is present in the reaction mixture when starch is neither in the rate equation know in the reaction equation (2)

XX

Answer 10

Starch is an indicator (that reacts with iodine)

(Starch changes colour when all the thiosulfate is used up)

Time taken for the formation of the blue black complex (can be used to calculate reaction rate)