DF - Kinetics *02

Question 1

catalyst

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

catalysis

Answer 2

speeding up a chemical reaction by using a catalyst

Question 3

catalyst poison

Answer 3

catalysts can be poisoned so they don’t work anymore

1. carbon monoxide, CO, poisons the solid iron catalyst used in the Haber process
2. lead poisons the catalyst in catalytic converters which was a problem when lead was added to petrols

heterogeneous catalysts often get poisoned because the poison clings to the catalyst’s surface more strongly than the reactant does. so the catalyst is prevented from getting involved in the reaction its meant to be speeding up

Question 4

heterogeneous

Answer 4

heterogeneous catalysts are in a different physical state from the reactants

eg. catalyst solid, the reactants are gases or liquids

iron in Haber process and Lead in catalytic converters

Question 5

model to explain function of heterogeneous catalyst

Answer 5

soild heterogeneous catalysts can provide a surface for a reaction to take place on.

1. ADSORPTION - reactant molecules arrive at the surface and bond with the solid catalyst.
2. the bond between the reactant’s atoms are weakened and break up. This forms radicals, the radicals then get together and form new molecules
3. DESORPTION - the new molecules are then detached from the catalyst

(need to draw this!)

Question 6

explain the needed strength of adsorption

Answer 6

mustn’t be too strong or the catalyst wont let go of the atoms after the reaction BUT strong enough to weaken bonds between the reactant molecules or that he new molecules can form

Question 7

cracking

Answer 7

1. short-chain hydrocarbons more useful than long ones (5-10 used in petrol)
2. long-chain alkenes can be cracked (broken up) into smaller hydrocarbons
3. the products of cracking are random as the same molecule can give different cracking products

Question 8

use of catalysts in cracking

Answer 8

without catalysts, the cracking process requires extremely high temp. and pressure which makes it expensive

By passing hydrocarbon vapour over a heated solid catalyst cracking can take place at much lower temperatures (around 450c) and pressures, saving a lot of money