rates

Question 1

when the intial conc of a is 1moldm-3 the half life is 20 minutes, if the conc is 2moldm-3 what is the half life

Answer 1

still 20 because it remains constant despite the concentration changing bc the reactant is still a

Question 2

give two different measurements you could make in a school lab while this reaction goes on to calculator the ror

Answer 2

collect the gas and measure the volume collected over time, let the gas escape and measure the decrease in mass over time

Question 3

How else can rate be measured

Answer 3

change in ph as conc of h+ ions change, amount of mass lost or volume of gas produced.

Question 4

why are different volumes of water added to each solution of propanone

Answer 4

to make the volumes constant for all mixtures, so that the volume of propanone is proportional to its concentration

Question 5

explain quantitatively why doubling the temperature has a much greater effect on the rate of reaction than doubling the conc of e

Answer 5

reactions occur when molecules have an energy equal to or in excess of the activation energy, doubling the temp would cause many more molecules to have this however doubling the conc of e only doubles this number with this e

Question 6

when naming with a hydroxy and a methyl group what goes firs

Answer 6

the hydroxy

Question 7

By considering the mechanism of the reaction explain why the product of butanone with reduction of nabh4 has no effect on the plane of polarised light (6 marks)

Answer 7

first- formation of product, nucleophillic attack on a planar carbonyl group, the h- can attack from either side.
draw it and talk about how it exists in two chiral forms and so equal amounts of the enantiomers can be formed so this makes a racemix mixture
optical isomers rotate the plane of polarised light in opp directions by the same amounts but because in a racemix mixture it is equimolar the effect cancels out and it therefore doesnt rotate the plane of polarised light

Question 8

why could a reac with something be slow

Answer 8

weak acid

Question 9

calibration curves interpret

Answer 9

firstly make solutions up, measure absorbance using colorimeter. more concentrated its darker so more light absorbed so number higher. you can also measure colour change using a disappearing cross

Question 10

larger k

Answer 10

faster reaction, but it only changes w temp.

Question 11

important thing about k in one experiment

Answer 11

k same for all experiments at the same temp therefore you can work out k and then sub values in for the rate.

Question 12

why is a c-br slow reac

Answer 12

as c-br is a strong bond

Question 13

why is oh- fast reac

Answer 13

as there is a good chance of collisions if we increase oh- conc

Question 14

why can a mechanism be favoured

Answer 14

if the rds matches the ratio in the rate equation

Question 15

as activation energy decreases

Answer 15

k increases as it drops more particles can react as they will have sufficient energy

Question 16

as we increase temp

Answer 16

k increases as particles have more energy

Question 17

explain qualitavely why doubling the temp has a much greater effect on the rate of reaction than doubling the conc of e

Answer 17

doubling temp means that many more molecules have sufficient energy to collide and successfully react as they have energy higher than the activation energy, whereas doubling e only doubles the number of particles with this energy.

Question 18

working out a justification of a order from a graph

Answer 18

initial rate, and you need rate at a specific conc
1)do initial rate/ ratea conc
2)do initial conc/specific conc
answer to part 2 (doing what the order says so square that, and that should equal answer from part 1)

Question 19

using x to represent the ester write a rate equation for the hydrolysis for this reaction``

Answer 19

rate= K (X) (OH-) square brackets

Question 20

in a second exp at the same temp water was added to the original mixture so the total volume doubled what is the initial conc

Answer 20

remember water dilutes it so doubling volume of water halves the conc. and k stays the same at the same temp therefore plug values in

Question 21

What is meant by the term order of reaction with respect to A?

Answer 21

Power (or index or shown as x in [ ]x

) of concentration term