DF - Catalysts

Question 1

What does a catalyst do?

Answer 1

Increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy. The catalyst is chemically unchanged at the end of the reaction.

Question 2

What is catalysis?

Answer 2

Speeding up a chemical reaction by using a catalyst.

Question 3

When is an iron catalyst used?

Answer 3

In the haber process to make ammonia.

Question 4

What type of chain hydrocarbons are more useful?

Answer 4

Short chain.

Question 5

How can long chain hydrocarbons be turned into short chain hydrocarbons?

Answer 5

Broken up in the cracking process.

Question 6

How are the products of cracking determined?

Answer 6

It is random and the same molecule can give different cracking products.

Question 7

What would the consequences be for cracking is a catalyst wasn’t used?

Answer 7

It requires extremely high temperatures and pressures making it expensive.

Question 8

How does cracking take place?

Answer 8

By passing hydrocarbon vapour over a heated solid catalyst.

Question 9

What are the benefits of passing hydrocarbon vapour over a heated solid catalyst for the cracking process?

Answer 9

Cracking can take place at much lower temperatures (around 450 degrees celsius) and pressures, saving a lot of money.

Question 10

What are heterogeneous catalysts?

Answer 10

Catalysts in a different physical state from the reactants.

Question 11

What catalyst is used in the haber process?

Answer 11

Iron.

Question 12

Why is iron a heterogeneous catalyst in the haber process?

Answer 12

Iron is a solid and the reactants are hydrogen gas and nitrogen gas.

Question 13

What is platinum catalyst used in?

Answer 13

Catalytic converters.

Question 14

What type of catalyst do catalytic converters use?

Answer 14

Heterogeneous platinum catalysts.

Question 15

What do catalytic converters do?

Answer 15

Stop pollutants coming out of the engine. They turn them to harmless gases like water vapour and nitrogen, or to less harmful ones like carbon dioxide.

Question 16

How do heterogeneous catalysts work?

Answer 16

The reactions happen on the solid catalyst. They can provide a surface for a reaction to take place on.

Question 17

How does a reaction take place on a heterogeneous catalyst?

Answer 17

Reactant molecules arrive at the surface and bond with the solid catalyst. This is called adsorption.

The bonds between the reactant’s atoms are weakened and break up. This forms radicals - atoms or molecules with unpaired electrons. These radicals then get together and make new molecules.

The new molecules are then detached from the catalyst. This is called desorption.

Question 18

What is it called when the reactant molecules arrive at the surface and bond with the solid catalyst?

Answer 18

Adsorption.

Question 19

What is the first stage in how a heterogeneous catalyst works?

Answer 19

Adsorption.

Question 20

What is it called when the new molecules are then detached from the catalyst?

Answer 20

Desorption.

Question 21

What does it mean if a catalyst becomes poisoned?

Answer 21

They don’t work anymore.

Question 22

What poisons the iron catalyst in the haber process?

Answer 22

CO

Question 23

What poisons the catalyst in catalytic converters?

Answer 23

Lead (but now we get unleaded petrol).

Question 24

Why do heterogeneous catalysts get poisoned?

Answer 24

Because the poison clings to the catalysts surface more strongly than the reactant does. So the catalyst is prevented from getting involved in the reaction it’s meant to be speeding up.