11A.6

Question 1

what is Arrhenius equation

Answer 1

k= Ke^(-Ea/RT)

Question 2

as the temperature increases the rate of reaction increases. why is that

Answer 2

1. a greater fraction of molecules would have energy equal to or greater than the Ea
2. more frequent collisions (but less significant so can be ignored)

Question 3

what is A in the Arrhenius equation

Answer 3

it is a constant known as the pre-exponential factor (the measure of the rate at which collisions occur irrespective of their energy

Question 4

if we take the natural logarithms of the Arrhenius equation we can obtain

Answer 4

lnk = - (Ea/R x 1/t )+ ln A

Question 5

if we polt Ink agganist 1/t we get {lnk = - ( /R x 1/t )+ ln A}

Answer 5

a straight line with the - Ea/R as the gradient and ln A as the c intercept, this allows us to calculate Ea experimentally

Question 6

is it true that Ea and A are constant across multiple temperatures

Answer 6

this is not true but the change in their values is so small compared to the effect of temperature on the rate, so it can be significant and we can say that the relationship between Ink and -1/T is linear

Question 7

what does e^(-Ea/RT) represent

Answer 7

the fraction of collisions that have energy equal to or greater that the activation energy

Question 8

is the fraction of collision with energy = or greater than Ea the same as the fraction of molecules with that energy

Answer 8

no, it isn’t but at high energies the difference is insignificant, this is why we draw an energy distribution curve and not a collision frequency curve when demonstrating the effect of temperature on the collision frequency

Question 9

reactions with high Ea are

Answer 9

slow, but the rate increase rapidly with an increase in temperature

Question 10

reactions with small Ea are

Answer 10

fast, the rate doesn’t increase rapidly with an increase in temperature

Question 11

catalyst reactions have

Answer 11

small Ea

Question 12

while drawing a profile diagram the intermediate has a

Answer 12

energy minimum

Question 13

how do you draw an Sn2 profile diagrams

Answer 13

page 24

Question 14

does the intermediate last longer than the transition state

Answer 14

yes

Question 15

when does the transition state occur

Answer 15

when molecules are in contact with one another

Question 16

was the number of alkyl groups donating electrons towards the positive carbon atom increase

Answer 16

the stability of the carbocation increases, and the activation energy leading to its formation also dearses

Question 17

the Sn1 reactions increases

Answer 17

as the number of alkyl groups increases primary < secondary < tertiary

Question 18

The more alkyl groups around the central carbon atom

Answer 18

the more crowded the transition state will be and the higher the activation energy making Sn2 reactions increase in the order of tertiary < secondary < primary