Topic 18: Kinetics

Question 1

Rate of reaction at particular instant

Answer 1

rate = change in conc. / time

Question 2

The order of a reaction (with respect to a species)

Answer 2

The power to which the conc. of that species is raised in the rate expression.

Question 3

The overall rate of a reaction

Answer 3

The sum of all the orders of reaction in the rate expression.

Question 4

Units for rate

Answer 4

mol dm−³ s−¹

Question 5

How do you determine rate from conc-time graph?

Answer 5

Draw a tangents at different point these determine the rates at certain points of the reaction.

Question 6

Determining order of a reaction from rate-conc. graphs

Answer 6

zero order- horizontal straight line
1st order - straight line through the origin
2nd order - wont be a straight line, plot rate against [X]^2 if straight line, order 2

Question 7

Using initial rate to determine order with respect to each species.

Answer 7

As initial conc of species is *2 if order 2 rate will *2^2. If initial conc of species is *3 rate will *3^3 if order 2.

Question 8

General rule for increase in temp and rate of reaction.

Answer 8

As temp increases by 10K, rate of reaction doubles.

Question 9

What is the effect of increasing the temperature on k (the rate constant)?

Answer 9

Increasing the temperature increases the rate constant.
As you increase the temperature more particles have energy greater than or equal to the activation energy.
So increased frequency of successful collisions.

Question 10

The Arrhenius Equation

Answer 10

​k =Ae^(-Ea/RT)

Question 11

A in the Arrhenius equation

Answer 11

A pre-exponential factor, the frequency of correctly oriented collisions.

Question 12

Ea

Answer 12

Activation Energy is the minimum amount of energy particles require in order for a successful collision to occur causing the reaction to happen.

Question 13

R

Answer 13

The gas constant (usually 8.31)

Question 14

e^(-Ea/RT)

Answer 14

The fraction of collisions with enough energy to react.

Question 15

Unit for T in Arrhenius equation

Answer 15

K

Question 16

Unit for -Ea in Arrhenius equation

Answer 16

Jmol^-1

Question 17

Unit for R in Arrhenius equation

Answer 17

JK^-1mol^-1

Question 18

Log form of Arrhenius equation

Answer 18

lnk=ln(Ae^(−Ea/RT))
= (−Ea/R)(1/T)+lnA
y=mx+c

Question 19

How to use the log form of the Arrhenius equation

Answer 19

Drawing a graph of 1/T and lnk, the gradient will be (-Ea/R) and can be used to determine the activation energy.

Question 20

Rate Determining Step

Answer 20

The slowest step in the reaction so it determines the overall rate.

Question 21

Anything _____ the rate determining step wont affect the rate.

Answer 21

After, these will be quick in comparison and not affect the rate or be in the rate equation, steps before will potentially be.

Question 22

Determining the rate determining step

Answer 22

Either the slowest, the has the reactants in the rate expression, the number of those reactants add to their respective order.
a+b=c
b+c=d
d+c=e
rate equation = k[a][b]^2
step 2 is the rate determining step.

Question 23

The iodine clock reaction step 1

Answer 23

H202(aq)+2I-(aq)+2H+(aq) —-> I2(2)+2H20(l) rate determining step (hydrogen peroxide) (potassium iodide)(sulfuric acid)

Question 24

The iodine clock reaction step 2

Answer 24

I2(aq) +2S203^-2(aq)——> S406^-2(aq)+2I-(aq) (sodium thiosulfate) (tetrathionate) Excess iodine will react with the added starch and

Question 25

How does the iodine clock reaction work?

Answer 25

Step 1 then Step 2. Excess iodine will react with the added starch and turn it from colourless and clear to blue black. Time it with varying conc. of H202.