3.2.2 - Reaction Rates

Question 1

What will effect the rate of reaction?

Answer 1

• particle size
• temperature
• concentration
• pressure
• catalyst

Question 2

How will particle size affect the rate of reaction?

Answer 2

Smaller particles have a larger surface area, therefore more collisions per second and more of those collisions result in a reaction.

Question 3

How does temperature affect the rate of reaction?

Answer 3

Particles have more kinetic energy, therefore increased force of collisions and a higher frequency of collisions per second. Moreover move particles have the same or larger amount of energy than the activation energy, so more successful collisions per second.

Question 4

How does concentration increase the rate of reaction?q

Answer 4

As concentration increases there are more particles per unit volume, therefore more collisions per second resulting in more reaction per second hence an increase in the rate of reaction.

Question 5

How does pressure increase the rate of reaction?

Answer 5

As pressure increases there are more particles per unit volume, therefore more collisions per second resulting in more reactions per second hence an increased rate of reaction.

Question 6

What are the axis for the Boltzmann distribution?

Answer 6

X = energy kJmol-1
Y = number of molecules.

Question 7

What does a Boltzmann distribution look like?

Answer 7

Curve which is swayed towards the left.

Question 8

What does an increased temperature look like on a Boltzmann distribution?

Answer 8

A curve which is lower but more centrally skewed. More particles past the activation energy.

Question 9

What does a catalyst look like on a Boltzmann distribution?

Answer 9

A vertical line further to the left than the activation energy.

Question 10

What are catalyst?

Answer 10

Increase the rate of reaction by providing an alternative pathway of lower activation energy. The catalyst remains chemically unchanged at the end of the reaction.

Question 11

What is a heterogenous catalyst?

Answer 11

One that is in a different phase from the other reactants.

Question 12

What is a homogenous catalyst?

Answer 12

One that is in the same phase as the reactants.

Question 13

Example of heterogenous catalyst?

Answer 13

Iron, in the Haber process.

Question 14

Example of homogenous catalyst?

Answer 14

H+ in the production of methyl ethanoate and water.

Question 15

What are the axis for an energy profile diagram?

Answer 15

X = enthalpy 
Y = reaction pathway

Question 16

Why is a catalyst good for the Haber process?

Answer 16

If a catalyst wasn’t there the temperature would have to be raised in order for the reaction to be quick enough. This would be expensive and would also reduce the amount of ammonia produced.

Question 17

Why is a catalyst useful in the production of poly(ethene)?

Answer 17

It makes the product more dense, rigid and have a higher melting point.

Question 18

How do catalysts provide environmental sustainability?

Answer 18

They reduce waste by allowing a different reaction to be used with a better atom economy.

Question 19

Why are catalytic converters good?

Answer 19

They are made from alloys of platinum, palladium and rhodium and they reduce the pollution released into the atmosphere by speeding up the reaction, 2CO + 2NO -> 2CO2 + N2

Question 20

Rate of reaction =

Answer 20

Amount of reaction used or product formed / time

Question 21

How can you investigate reaction rates?

Answer 21

Change in mass / volume of gas given off.

Question 22

Explain the reaction using change in mass.

Answer 22

• When product is gas, its formation can be measured using a mass balance.
• the amount of product formed is the mass disappearing from the container.
• when the reaction starts, you should start a timer.
• take mass measurements at regular time intervals.

Question 23

Is the change in mass method good?

Answer 23

It’s very accurate but can be dangerous if toxic gases are released into the room.

Question 24

Explain volume of gas given off experiment

Answer 24

• use a gas syringe to measure the volume of product formed.

- measure the amount of gas formed at regular time intervals.

Question 25

Is the volume of gas given off experiment good?

Answer 25

Accurate, but vigorous reactions can blow the plunger out of the syringe.

Question 26

How can you work out the rate of reaction from a graph?

Answer 26

The gradient.

Question 27

What are the units for rate of reaction?

Answer 27

Y/x (e.g cm3 min-1)

Question 28

How can you work out the rate on a curve?

Answer 28

Draw a tangent to the curve from where you are asked (e.g 3 mins) and then draw a triangle and work out the gradient of that line.