10.2 catalysts

catalyst

a substance that changes the rate of a chemical reaction without undergoing any permanent change itself. a catalyst increases the rate of a chemical reaction by providing an alternate reaction pathway of lower activation energy

what does a catalyst do

• the catalyst is not used up in the chemical reaction

• 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 of the reaction the catalyst is regenerated

homogeneous catalyst

• a homogeneous catalyst has the same physical state as the reactants

• the catalyst reacts with the reactants to form an intermediate. The intermediate then breaks down to give the product and regenerates the catalyst

• eg. making esters with sulphuric acid as a catalyst

• ozone depletion using chlorine radicals as a catalyst

heterogeneous catalyst

• has a different physical state from the reactants

• heterogeneous catalysts are usually solids in contact with gaseous reactants or reactants in solution

• reactant molecules are weekly bonded onto the surface of the catalyst where the reaction takes place. After reaction, the product molecules leave the surface of the catalyst by desorption

• making ammonia (haber process using Fe catalyst)

• hydrogenation of alkenes (nickel catalyst)

how are catalysts used for sustainability and economic importance

• catalysts increase the rate of many industrial chemical reactions by lowering the activation energy

• this then reduces the temperature needed for the process and the energy requirements

• if a chemical process requires less energy, then less electricity or fossil fuel is used. This makes the product faster and less energy can cut costs + increase profitability

• the economic advantages of using a catalyst outweigh any costs associated with developing a catalytic process

• the modern focus on sustainability requires industry to operate processes with high atom economy and fewer pollutants. using less fossil fuels will cut emissions of carbon dioxide, a gas linked to global warming