3.1.5 Kinetics

Question 1

What are the 5 main factors affecting rate of reaction?

Answer 1

• Conc.
• Pressure.
• Temp.
• SA.
• Catalyst.

Question 2

Define rate of reaction.

Answer 2

• Change in conc of a reactant or product in a given period of time.

Question 3

Define activation energy.

Answer 3

• Minimum amount of energy which reacting particles require for successful collision.

Question 4

How does conc affect ror?

Answer 4

• Conc increase.
• More particles of reactant present.
• More successful collisions in given period of time.
• ∴ ror increases.

Question 5

How does pressure affect ror?

Answer 5

• Pressure increase in gaseous reaction system.
• Particles forced closer together.
• Leads to more successful collisions in given period of time.
• ∴ ror increases.

Question 6

How does temp affect ror?

Answer 6

• Temp increase, particles gain energy + move faster.
• More frequent successful collisions in given period of time.
• ∴ ror increases.

Question 7

How does SA affect ror?

Answer 7

• Increasing SA increases exposed surface of reactants.
• Increase in number of successful collisions in given period of time.
• ∴ ror increases.

Question 8

How do catalysts affect ror?

Answer 8

• Catalyst increase ror wo/ being used up.
• Provide alternative reaction pathway of lower activation energy.
• More successful collisions in given period of time.
• ∴ ror increases.

Question 9

Why are catalysts important in industrial processes?

Answer 9

• Speed up reactions ∴ reduce costs.

Question 10

What type of graph can be used to show exothermic and endothermic reactions?

Answer 10

• Enthalpy profile diagrams or reaction profile diagrams.

Question 11

Draw an enthalpy diagram for an exothermic reaction.

Answer 11

…

Question 12

Draw an enthalpy diagram for an endothermic reaction.

Answer 12

…

Question 13

What is a Maxwell-Boltzmann distibution?

Answer 13

• Plot of number of gaseous molecules against energy at fixed temp.

Question 14

What type of molecules is a Maxwell-Boltzmann distribution used for?

Answer 14

• Gaseous molecules.

Question 15

What is a Maxwell-Boltzmann distribution also called?

Answer 15

• Molecular energy distribution graph.
• Distribution of molecular energies.

Question 16

What is important about the temp in a Maxwell-Boltzmann distribution?

Answer 16

• Constant.

Question 17

What does a Maxwell-Boltzmann distribution look like at a constant temp?

Answer 17

• Roughly normal distribution which is asymptotic to the horizontal axis.

Question 18

What are the 5 main points from a Maxwell-Boltzmann distribution at constant temp?

Answer 18

• 0 molecules have 0 energy ∴ starts at origin.
• Area under graph = total no. molecules present.
• Peak is most probable energy of molecules (Emp).
• Most molecules have moderate energy in middle of graph.
• Very few molecules have high energy but asymptote as no upper limit to the energy of particles.

Question 19

How is activation energy represented on a Maxwell-Boltzmann distribution?

Answer 19

• Ea.

Question 20

What are on the x and y axis of a Maxwell-Boltzmann distribution?

Answer 20

• x –> Energy.
• y –> No. molecules.

Question 21

Using a M-B distribution how does increasing a catalyst increase ror?

Answer 21

• More area above activation energy.
• ∴ more molecules w sufficient energy for successful collisions.

Question 22

Does using a catalyst affect the shape of a M-B distribution?

Answer 22

• No bc total no. molecules + temp are same.

Question 23

Does increasing temp affect the shape of a M-B distribution?

Answer 23

• Yes because increase in energy of reactants.

Question 24

What 4 things should you note when sketching a distribution for the same sample of gas at a lower or higher temp?

Answer 24

• Lower –> distributions moved to left + peak is higher.
• Higher –> moved to right + lower peak.
• Graphs should only cross once.
• Curves always start at origin + are asymptotic.

Question 25

Using a M-B distribution how does increasing temp affect ror?

Answer 25

- Higher temp, more area under graph at Ea - ∴ more reactant molecules to undergo a successful collision. - ∴ higher ror at higher temp.

Question 26

What affect does a small increase in temp have on ror?

Answer 26

- Large increase in ror as significant increase in no. molecules w enough energy to undergo successful collisions.

Question 27

Does increasing conc affect the shape of a M-B distribution?

Answer 27

- Same basic shape. - Higher peak. - Emp (most probable energy) in same place.

Question 28

Using a M-B distribution how does increasing conc affect ror?

Answer 28

- Higher conc, higher no. reactant molecules. - Overall area under increases. - ∴ more shaded area above Ea. - Increase in no. molecules which have energy to undergo successful collision increases. - ∴ higher ror.

Question 29

How is Ea affected by increasing conc?

Answer 29

- Higher conc more area of reactant molecules that have Ea.

Question 30

Does incresing temp or conc have a more significant affect on ror?

Answer 30

- Increasing temp.