5.1.1 How Fast?

Question 1

What’s the rate equation

Answer 1

Rate = k [A]^n

Question 2

What’s the order of the reaction

Answer 2

The power that the concentration of a reactant is raised to

Question 3

What’s overall order

Answer 3

Overall effect of the concentration of all reactants on rate of reaction

Question 4

Definition of half life

Answer 4

Time taken for half of a reactant to be used up

Question 5

Definition of rate-determining step

Answer 5

Slowest step in a multi-step reaction

Question 6

How does 0 order effect rate

Answer 6

It doesn’t

Question 7

How does first order effect rate

Answer 7

Rate = k [A]^1

Question 8

How does second order effect rate

Answer 8

Rate = k[A]^2

Question 9

Shape of a concentration-time graph for zero order reaction

Answer 9

Straight line with negative gradient

Question 10

Shape of a concentration-time graph for a first order reaction

Answer 10

Downward curve with decreasing gradient over time

Question 11

Half life in first order conc-time graph

Answer 11

Constant

Question 12

Equation involving half life

Answer 12

K= ln2 ÷ half life

Question 13

Shape of a rate-conc graph for zero order

Answer 13

Horizontal straight line

Question 14

Shape of a rate-conc graph for first order

Answer 14

Straight line graph through origin, rate is directly proportional to conc

Question 15

Shape of a rate-conc graph for second order

Answer 15

Upward curve, increasing gradient

Question 16

How to find rate constant from a first order rate-conc graph

Answer 16

Gradient of the line

Question 17

How to determine rate via continuous monitoring

Answer 17

Prepare standard solutions of known conc of iodine
Select green/blue filter on colorimeter
Zero colorimeter with water
Measure absorbance readings of the solutions
Plot calibration curve of absorbance against iodine conc
Carry out reaction between propanone and iodine, take absorbance readings at measured time intervals
Use calibration curve to measure conc of iodine at each absorbance reading
Plot graph of concentration of iodine against time, determine order of reaction

Question 18

How to determine rate via initial rates method

Answer 18

Solution is colourless at beginning and t is measured for blue black colour of starch-iodide to appear
Repeated with different concentrations, another chemical delays colour change, when its all used up, blue-black colour forms
Initial rate proportional to 1÷t
Graph of 1÷ t against conc plotted, shape matched to order
Then reaction done whilst changing conc of a different reactant

Question 19

How to predict reaction mechanisms

Answer 19

Rate equation only includes reacting species involved in RDS
Orders in rate equation match number of species in RDS

Question 20

Effect of temperature on rate constant

Answer 20

Increases rate constant with increased temp
Increasing temperature shifts Boltzmann distribution to the right and increases proportion of particles that exceed the activation energy
As temp increases, particles move faster and collide more frequently

Question 21

Rearranged Arrhenius equation

Answer 21

lnk = -Ea ÷ RT + lnA