9:Kinetics

Question 1

What is the rate of reaction?

Answer 1

Change in concentration of a reactant or product over time

Question 2

What are the two conditions required for a successful collision?

Answer 2

• correct orientation
• energy equal to or more than the activation energy

Question 3

What is the initial rate?

Answer 3

The reaction rate at time zero

Question 4

What is steric hindrance?

Answer 4

When shapes of the molecules influences reactions

Question 5

What is the effect of increased concentration on the rate of a reaction?

Answer 5

More reacting particles in unit volume, distance between particles is shorter. So increases chance of collisions between particles.

Question 6

What is the effect of increased pressure on the rate of a reaction?

Answer 6

Volume decreases, more reacting particles in unit volume. Distance between particles is shorter, increased chance of collision between particles

Question 7

What is the effect of increased surface area on the rate of a reaction?

Answer 7

Higher chance of collision between particles due to more area exposed

Question 8

What does the Maxwell-Boltzmann distribution curve show?

Answer 8

The range of kinetic energies the particles in a gaseous system posses at a particular temperature

Question 9

What is the area under the curve of a Maxwell-Boltzmann distribution graph?

Answer 9

The total number of particles

Question 10

What happens to the Maxwell-Boltzmann distribution curve when you increase the temperature?

Answer 10

The maximum point of the curve shifts to the right and gets lower.

Question 11

Why does the rate of reaction increase when you increase the temperature?

Answer 11

1) more particles have equal to or more energy than the activation energy
2) particles move faster and further

Question 12

How do catalysts work?

Answer 12

Provides an alternative reaction path that requires a lower activation energy

Question 13

What happens to the Maxwell-Boltzmann distribution graph when you add a catalyst?

Answer 13

The activation energy point (Ea) is moved to the left. Curve stays the same

Question 14

Why are catalysts generally used in industry?

Answer 14

1) lowers energy cost
2) allows for a lower temp + pressure to be used for the same rate
3) can also give a higher atom economy

Question 15

What are heterogenous catalysts?

Answer 15

Catalysts that an in a different phase or state to the species in the reaction.

Question 16

Why do transition metals make good catalysts?

Answer 16

They have variable oxidation states

Question 17

How do solid catalysts work?

Answer 17

1) By adsorbing molecules onto an active site on the surface of the catalyst.
2) These active sites increase the proximity of molecules and weaken the covalent bonds in the molecules so that reactions occur more easily

Question 18

What is activation energy?

Answer 18

The minimum energy that colliding particles must have to cause a reaction
- only collisions with energy more than or equal to the activation energy results in a bond breaking and forming

Question 19

Why are solid heterogenous catalysts used in industry?

Answer 19

To give a surface for the reaction to occur on

Question 20

What is the effect of increased temperature on the rate of a reaction?

Answer 20

Increases kinetic energy means more collisions and more particles with equal to or more activation energy

Question 21

How do heterogenous catalysts work? - in the case of solid-based catalyst and gaseous reactants

Answer 21

1) The reactant diffuses to the catalyst and ‘lands’ on the surface
2) Reactants the get adsorbed onto the surface of the catalyst
3) After adsorption has taken place, bonds within the reactant are weakened to the point where the reaction can start to take place, and an intermediate is formed
4) After the reaction has completed, the product remains adsorbed on the surface of the catalyst
5) The product will desire from the surface of the catalyst and will diffuse away

Question 22

What are the economic benefits of a catalyst?

Answer 22

• Allow reactions to occur at lower temperatures and pressures, saving energy
• Increase reaction rate, giving higher productivity