Topic 5- Kinetics Part 2

Question 1

Describe the format of heterogeneous catalysis?

Give an example of this?

Describe the action of heterogeneous catalysis?

Give an example of this?

Answer 1

Catalysts are in a different phase to the reactants

eg A solid catalyst in a gaseous reaction

Takes place at active sites on the surface of a solid

Gases are absorbed onto the surface where they form weak bonds with metal bonds.

Question 2

Describe the format of homogeneous catalysis?

Give an example of this?

Describe the action of homogeneous catalysis?

Answer 2

Catalysts are in the same phase to the reactants

eg A gaseous catalyst in a gaseous reaction

Takes place throughout the gaseous mixture.

Question 3

Describe the stage of adsorption in catalysis?

Describe the stage of reaction in catalysis?

Describe the stage of desorption in catalysis?

Answer 3

Stage 1-
Incoming species lands on an active site and forms bonds with the catalyst. It may use some of the bonding electrons in the molecules this weakening them and making a subsequent reaction easier

Stage 2 (and 3)-
Absorbed gases may be held on the surface in just the right orientation for a reaction to occur.
This increases the chances of favourable collisions taking place

Stage 4-
This a re-arrangement of electrons and the products are then released from the active sites.

Question 4

What are the three ways to measure reaction rates?

Answer 4

• Timing how long a precipitate takes to form
• Measuring a decrease in mass
• Measuring the volume of gas given off.

Question 5

What happens if you increase the concentration of reactants in a solution?

What does this result in?

What happens if collisions occur more frequently?

What does increasing the concentration do to reactions?

Answer 5

The particles will on average be closer together

If they’re closer, they’ll collide more often

They’ll have more chances to react

Increases the rate of reaction.

Question 6

What happens if a reaction involves gases and you increase the pressure?

What does this mean happens to collisions?

What does increasing the pressure do to certain reactions?

Answer 6

Raising the pressure pushes all of the gas particles closer together, making them more likely to collide

So collisions take place more frequently and the reaction rate increases

Increases the rate of reaction- if gases are present.