3.2.2 Catalysts

Question 1

define catalyst

Answer 1

A catalyst is a substance that changes the rate of a chemical reaction without undergoing any permenant change itself.

Question 2

what could happen to catalysts in a reaction

Answer 2

• The catalyst is not used up
• The catalyst may react with a reactant to form an intermediate or may provide a surface on which the reaction can take place
• At the end the catalyst is regenerated

Question 3

What does a catalyst do in a reaction

Answer 3

A catalyst increases the rate of a chemical reaction by providing an alternative reaction pathway of lower activation energy.

Question 4

how is activation energy with a catalyst represented on an enthalpy profile diagram

Answer 4

Ec

Question 5

what are the types of catalysts

Answer 5

• Heterogeneous
• Homogeneous

Question 6

Explain what a homogeneous catalyst is and does

Answer 6

A catalyst that has the same physical state as the reactants. The catalyst reacts with the reactants to for an intermidiate. The intermediate then breaks down to give the producct and regenerated the catalyst.

Question 7

Explain what a heterogeneous catalyst is and does

Answer 7

A heterogeneous catalyst is a catalyst that has a different physical state from the reactants. They are usually solids in contact with gaseous reactants or reactants in a solution. Reactant molecules are absorbed (weakly bonded) onto the surface of the catalyst, where the reaction takes place. After the reaction, the product molecules leave the surface of the catalyst by desorption.

Question 8

Give an example of how heterogeneous catalysts are used in real life

Answer 8

All petrol vehicals in the UK must be fitted with a catalytic converter.
Catalytic converters contain a catalyst made of platinum, rhodium and palladium on a honeycomb mesh (provides large surface area). The hot exhaust gases pass over this heterogeneous catalyst and harmful gases are converted into less harmful products.
combustion in a petrol engine produces CO and nitrogen monoxide, the converter turns it into CO₂ and nitrogen products that are non-toxic.

Question 9

why do industries use catalysts

Answer 9

• Catalysts increase the the rate of many industrial chemical reactions by lowering the Ea. This then reduces the temperature needed for te process and the energy requirements.
• if a chemical process requires less energy then less electricity/ fossil fuel is used.
• Making the product faster and using less energy can cut costs and increase profitability.
  (the economic advantages of using a catalyst outweigh any costs associated with developing a catalytic process.)
• Additionally the modern focus on sustainability requires industry to operate processes with high atom economies and fewer pollutants. Using less fossil fuels will cut emissions of carbon dioxide.

Question 10

Give some examples of industrial processes involving heterogeneous catalysts

Answer 10

• Haber process (Fe catalyst)
• hydrogenation of alkenes (Ni catalyst)