Kinetics

Question 1

When can reactions occur

Answer 1

Only when collisions take place between parties having sufficient energy and correct orientation

Question 2

What is this sufficient energy called

Answer 2

The activation energy

Question 3

Activation energy

Answer 3

The minimum energy required to start a reaction by breaking of bonds

Question 4

Why do most collisions not lead to a reaction

Answer 4

• may be insufficient energy

- orientation may be incorrect

Question 5

Rate of reaction

Answer 5

The change in concentration of a substance in a given time

Question 6

What are the units of rate

Answer 6

mol dm-3 s-1

Question 7

Why does the rate decrease as the reaction proceeds

Answer 7

The concentration of reactant falls

Question 8

What is the rate at a particular time equal to

Answer 8

The gradient at that time

Question 9

What is the correlation between concentration and rate

Answer 9

Increasing the concentration increases the rate

Question 10

Why does increasing concentration increase rate

Answer 10

• more particles per unit volume
• more collisions per second
• faster rate

Question 11

What is the correlation between pressure of gases and rate

Answer 11

Increasing the pressure increases the rate

Question 12

Why does increasing pressure gases increase rate

Answer 12

• more particles per unit volume
• more collisions per second
• faster rate

Question 13

What is the correlation between increasing SA of solids and rate

Answer 13

Increasing SA increases rate

Question 14

Why does increasing SA of solids increase rate

Answer 14

• more surface of solid exposed to other reactant
• more collisions per second
• rate is faster

Question 15

What is correlation between temperature and rate of reaction

Answer 15

Increasing temperature increases the rate

Question 16

Why does increasing temperature increase rate

Answer 16

• more particles have energy equal to or greater than activation energy
• more successful collisions
• rate is faster

Question 17

What does adding a catalyst do to rate of reaction

Answer 17

Increases it without it being used up

Question 18

Why does adding a catalyst increase rate of reaction

Answer 18

• provides alternate pathway
• lower activation energy
• more successful collisions
• faster rate

Question 19

Experiment between HCl and CaCO3 to show effect of conc on RoR

Answer 19

Add CaCO3 to HCl

Collect CO2 produced in a gas syringe

Record volume of CO2 at regular intervals

Produce graph of volume of CO2 against time

Question 20

What would a curve look like with same number of moles of acid but higher concentration

Answer 20

Steeper curve but levels of at same volume of CO2

Question 21

What would curve look like with half moles acid but same conc

Answer 21

Same steepness of curve but half final volume of CO2

Question 22

What does the reaction between sodium thiosulfate and hydrochloric acid produce

Answer 22

A precipitate of sulfur, sodium chloride and sulfur dioxide

Question 23

How can the rate of reaction between sodium sodium thiosulfate and hydrochloric acid be monitored

Answer 23

Measure time taken for cross to disappear from view

Cross obscured by PPT of sulfur

Question 24

What is measuring time taken for cross to disappear called

Answer 24

Initial rate method

Question 25

How can temp be known as accurately as possible in reaction between sodium thiosulfate and hydrochloric acid

Answer 25

Measure initial and final temp- take and use an average

Question 26

What could be used to prevent SO2 escaping from the reaction

Answer 26

Put a lid on the reaction vessel to minimise escape of CO2

Question 27

Why is a STOP bath used in reaction between sodium thiosulfate and hydrochloric acid

Answer 27

Both acid and sulfur dioxide can be neutralised

Question 28

What is the independent variable in the reaction between sodium thiosulfate and hydrochloric acid

Answer 28

Temperature

Question 29

What is the dependent variable in the reaction between sodium thiosulfate and hydrochloric acid

Answer 29

Time

Question 30

Why is the hazard associated with sulfur dioxide in this investigation considered to be low

Answer 30

Amount of SO2 low because solutions are dilute SO2 is soluble- doesn't all escape as a gas

Question 31

Why do the particles in a particular sample have a spread of energies when the samples collide

Answer 31

Energy is exchanged between them

Question 32

What does the Maxwell-Boltzmann distribution show

Answer 32

The distribution of energies of the particles within a sample

Question 33

What is the important feature of the maxwell boltzmann distribution that is seen at the origin of the graph

Answer 33

No particles have no energy

Question 34

What is the important feature of the maxwell boltzmann distribution that is seen at the end of the graph

Answer 34

The curve doesn't meet back with the x axis- no maximum energy

Question 35

What is the important feature of the maxwell boltzmann distribution at the highest point of the graph

Answer 35

The most likely every is not very high

Question 36

What does the shaded area represent on a maxwell Boltzmann distribution

Answer 36

Particles which will successfully collide

Question 37

How is the peak on a maxwell distribution curve at a higher temperature different

Answer 37

It's lower and to the right

Question 38

What is the difference between most probable energy in a maxwell Boltzmann distribution curve at a higher temp

Answer 38

The most probable energy is higher

Question 39

What is the change in area under the curve maxwell botlzmann at higher temp

Answer 39

Area under curve remains same

Question 40

How is the shaded area different in maxwell Boltzmann curve at higher temp

Answer 40

Shaded area now much larger as far more particles have energy equal to or greater than activation energy

Question 41

Why does a small temperature increase lead to a large increase in rate

Answer 41

Far more particles will now have energy greater than or equal to activation energy so far more successful collisions

Question 42

What is a catalyst

Answer 42

A substance which increases the rate of a chemical reaction without being changed in chemical composition or amount

Question 43

What does a catalyst provide

Answer 43

An alternative reaction route with a lower activation energy

Question 44

What is lowered and what is unchanged in the presence of a catalyst

Answer 44

Activation energy lowered but enthalpy not changed

Question 45

What does a maxwell Boltzmann distribution look like with a catalyst

Answer 45

Shaded area is bigger so more molecules have energy greater than or equal to activation energy More collisions are successful so rate of reaction increases