🔴🔸2.2 -rates Of Reaction

Question 1

What is the rate of reaction equation?

Answer 1

Change in concentration/time

Question 2

What is the units for rates of reaction

Answer 2

Mol dm-3 s-1

Question 3

Define rate of reaction

Answer 3

The change in concentration of a reactant or product per unit time

Question 4

Name the factors which affect the rate of reaction.

Answer 4

Concentration 
Temperature 
Particle size
Catalysts 
Light

Question 5

How does particle size affect ROR

Answer 5

Reducing particle size of a solid increases the surface area so the molecules are closer together and there is an increase in the number of collisions per unit time leading to an increase in rate of reaction

Question 6

How does light affect ROR

Answer 6

Some reactions are much more vigour OJ’s when carried or in bright light e.g photochlorination of methane

Question 7

Define activation energy

Answer 7

The minimum energy required to start a reaction by breaking bonds

Question 8

How do you calculate the entrapped change of a reaction?

Answer 8

Activation. Energy of foreword reaction - activation energy of backward reactions.

Question 9

What does the Boltzmann energy distribution curve show?

Answer 9

Shows the distribution of molecular energies in a gas,

only minority of molecules have values that exceeds activation energy (Ea

Question 10

LEARN DIAGRAM OF BOLTZMANN DISTRIBUTION CURVE

Answer 10

LEARN DIAGRAM OF BOLTZMANN DISTRIBUTION CURVE

Question 11

What happens to the Boltzmann distribution curve at higher temperatures

Answer 11

The average molecular energy will increase :: value of molecules with energy above activation also increases

Question 12

Define a catalyst

Answer 12

A substance that increases the rate of a chemical reaction without being used up in the process.
It increases the rate of reaction by providing an alternative route lowering activation energy.

Question 13

Describe the change in Boltzmann distribution curve with a catalyst

Answer 13

Activation energy lowers :: Ea point shifts to the left :: more molecules with sufficient activation energy for reaction

Question 14

Define homogenous catalyst

Answer 14

A catalyst in the same phase as the reactants

Question 15

Describe heterogenous catalyst

Answer 15

A catalyst in a different phase from the reactants

Question 16

Describe homogenous catalysts (2)

Answer 16

1) take an active part in a reaction rather than be an inactive spectator
2) typically involves liquid mixtures or substances in solution

Question 17

Name an example of a homogenous catalyst

Answer 17

Concentrated sulphuric acid in the formation of an ester from a carboxylic acid and an alcohol

Question 18

Describe heterogenous catalysts

Answer 18

• many are d block transition metals
• gases are absorbed on to the metal surface and react and the products desorb from the surface
• larger surface area=better catalyst works

Question 19

Name some important industrial processes involving the use of catalysts

Answer 19

• vanadium (V) oxide in the contact process (sulphuric acid manufacturing)
• Iron in the harbour process (ammonia production)

Question 20

Name two positives of catalysts

Answer 20

1. Good for economy (less energy for reactions :: efficient)
2. Good for environment

Question 21

Name some examples when enzymes (biological catalysts) are used

Answer 21

• lipase and protease in washing powders and detergents

- yeast and amalyse in brewing industry

Question 22

Name some benefits of enzymes as biological catalysts

Answer 22

• lower temperature and pressure can be used
• mild conditions and don’t harm fabrics or food
• biodegradable

Question 23

How would you measure the rate of reaction when A gas is produced?

Answer 23

Gas syringe

Question 24

How would you measure a change in gas pressure

Answer 24

Using a manometer or pressure sensor

Question 25

How can you measure a change in mass

Answer 25

Measure using weighing scales

Usually caused by gas being released

Question 26

What can the concentration of a substance changing colour be monitored by?

Answer 26

Colorimeter

Question 27

Name the parts to a colorimeter

Answer 27

Light source 
Lens 
Filter
Sample 
Detector 
(Diagram on pg 115)

Question 28

How does a colorimeter work?

Answer 28

• light source with filters selecting colour of light to be absorbed
• light passes through sample to detector
• detector develops an electrical signal which is proportional to intensity of light
• colorimeter has to be calibrated to show relationship between readings and concentration of species

Question 29

Name 2 examples of experiments where the initial concentrations of reactants are known and the time taken for each experiment is recorded

What is the rate equation in these reactions?

Answer 29

• ‘iodine clock’
• precipitation reactions

Rate is inversely proportional to 1/time

Question 30

Name the iodine clock reactions

Answer 30

H2O2 (aq) + 2H+(aq) + 2I-(aq) —> 2H2O (l) + I2 (aq)
(Slow)

Or

I2(aq) + 2S2O3 2- (aq) —> 2I-(aq) + S4O6 2-

Question 31

What is the normal reactions of iodine with starch solution?
What happens when thiosulfate ion is added in iodine clock reaction?

Answer 31

• blue
• if thiosulfate ion (reacts rapidly with iodine) no blue colour will appear until enough iodine has been formed to react with all the thiosulfate

Question 32

What does the iodine clock reaction measure?

Answer 32

Measures the rate of iodide ions being oxidised

Question 33

What should you plot for a iodine clock reaction on a graph to show relationship between H2O2 and rate

Answer 33

Plot graph of 1/time against volume of peroxide added

Question 34

What should you plot to show relationship between S2O3 2- and rate?

Answer 34

Plot 1/time against concentration of thiosulfate at constant acid concentration