10.2 Catalysts

Question 1

What is a catalyst?

Answer 1

• a catalyst is a substance that changes the rate of a chemical reaction without undergoing any change itself (without being used by the reaction itself) therefore is chemically unchanged.
• It may react with a reactant to form an intermediate
• At the end of the reaction the catalyst is regenerated
• A catalyst increases the rate of a chemical reaction by providing an alternative reaction pathway of a lower activation energy.

Question 2

What is a homogenous catalyst?

Answer 2

• same physical state as the reactants (for example, both the reactants and the catalysts are all in solution therefore is aqueous)
• Reacts with the reactants to form an intermediate
• Breaks down to give the product and regenerates/reform the catalyst

Question 3

What are heterogenous catalysts?

Answer 3

• different physical state from reactants (for example, the reactants are gases but the catalyst is a solid)
• Usually solids in contact with gaseous reactants or reactants in solution
• Reactant molecules are weakly bonded (adsorption) on to the surface of the catalyst where the reaction takes place- after the reaction the product molecules leave the surface of the catalyst by desorption
• Increasing the surface area of the catalyst increases the number of molecules that can react at the same time, increasing the rate of the reaction

Question 4

What are the advantages of using catalysts in the industry?

Answer 4

• catalysts increase the rate of many industrial chemical reaction by lowering the activation energy therefore reducing the temperature needed for the process
• Requires less energy, less electrical energy/fossil duels are used- making the product faster and the economic advantages with using a catalyst outweigh any costs (lowers production costs)
• High atom economies and fewer pollutants (catalytic converters are made of metal alloys, they speed the rate of reaction without being used itself) so reduces global warming

Where are catalysts used?

• they are used in the Haber process
• An example of a catalyst is iron and its used in the Haber process to make ammonia
• N2 + 3H2 → 2NH3 (its a reversible reaction and uses the Fe (s) catalyst)
• If we never used a catalyst, we would have to use a temperature high enough for the reaction to be quick enough- it will INCREASE fuel bills but also reduce the amount of ammonia produced

Question 5

What is autocatalysis?

Answer 5

• if a reaction product acts as a catalyst for the reaction- the reaction starts slowly and then speeds up as the products are formed