unit 4 - rates

Question 1

State four ways in which the rate of reaction can be measured ?

Answer 1

Through measuring the volume of gas produced/ mass lost

colorimtery

Titrimetric analysis

conductivity

Question 2

If the order is a) 1 b)2

what does the graph for half life look like?

Answer 2

a) constant curve
b) as half life halves, the concentration doubles

Question 3

if the order is a)0 b)1 c)2 what does the graph for concentration against time look life? what does the graph for rate against concentration look like?

Answer 3

a) for concentration against time - a y=x graph

for rate against concentration - straight line in x axis

b) for concentration against time- a curved graph

for rate against time - a y=x graph

c) for concentration against time - a steeper curved graph for rate against time- a curved graph

Question 4

Explain the iodine-propanone reaction

Answer 4

• small aliquots removed
• sodiom hydrogencarbonate qunches the reaction
• aliquots titrated with standard solution of sodium thiosulfate -starch is indicator at end point
• rate=k[H][CH3COCH3]
• Iodine is 0 order therefore is in the reaction after RDS
• Excess proponone therefore concentration stays constant
• If experiment is repeated , use twice as much proponone, the slope is found to be twice as steep

Question 5

Suggest the possible mechanism for the iodine- proanone reaction

Answer 5

• Protonation of Oxygen in propanone
• Electron in C=O shifts into carbon to form carbocation
• Carbocation loses proton
• CH bond broken
• iodine molecule acts as an electrophile
• electrophilic adddition occurs

Question 6

How to work out Ae using arhenius equation

Answer 6

gradient of Lnk against 1/T is -Ea/R

Question 7

what is the effect of temperature on rate?

Answer 7

increase in temperature increases the rate of reaction as the rate constant increases with temperature. Therefore smaller Ea means faster reaction

Question 8

Explain Sn1

Answer 8

Nucleophilic substitution that involves one reactant

Question 9

Explain Sn2

Answer 9

Nucleophilic substitution that involves two reactants