Catalysis

Question 1

catalyst

Answer 1

substance that speeds up the rate of a reaction without itself being consumed in the reaction

Question 2

Catalysts and their associated catalytic reactions come in three main types

Answer 2

homogeneous catalysts
heterogeneous catalysts
biocatalysts

Question 3

homogeneous catalysis

Answer 3

when the catalyst and the reactant(s) are in the same physical state or phase
often happens with gaseous catalyst-reactant pairs
organic acids in which the donated hydrogen atom is replaced by a metal, a number of compounds blending carbon and metal elements in some form, and carbonyl compounds joined to cobalt or iron

Question 4

conversion of persulphate and iodide ions to sulfate ion and iodine equation + explanation

Answer 4

S2O82- + 2 I- → 2 SO42- + I2

both reactants are negatively charged
electrostatic qualities are in opposition to their chemical qualities
iron ions, which carry a positive charge, are added to the mix, the iron “distracts” the negative charges and the reaction moves forward quickly

Question 5

naturally occurring gaseous homogeneous catalysis

Answer 5

conversion of oxygen gas, or O2, in the atmosphere to ozone, or O3, where oxygen radicals (O-) are intermediates. Here, ultraviolet light from the sun is the true catalyst, but every physical compound present is in the same (gas) state

Question 6

Heterogeneous Catalysis

Answer 6

when the catalyst and the reactant(s) are in different phases
inorganic – that is, non carbon-containing – solids such as elemental metals, sulfides and metallic salts, as well as a smattering of organic substances, among them hydroperoxides and ion exchangers.

Question 7

Zeolites

Answer 7

important class of heterogeneous catalysts
crystalline solids made up of repeating units of SiO4
Units of four of these joined molecules are linked together to form different ring and cage structures. The presence of an aluminium atom in the crystal creates a charge imbalance, which is offset by a proton (i.e., a hydrogen ion).

Question 8

How the heterogeneous catalyst works

Answer 8

One or more of the reactants are adsorbed onto the surface of the catalyst at active sites.
interaction between the surface of the catalyst and
the reactant molecules which makes them more reactive, e.g. bond weakening
reaction happens
both of the reactant molecules might be attached to the surface, or one might be attached and hit by the other one moving freely in the gas or liquid
product molecules are desorbed

Question 9

Adsorption

Answer 9

where something sticks to a surface

Question 10

Silver and Tungsten isn’t a good catalyst

Answer 10

Silver doesn’t form strong enough attachments with reactant molecules.
Tungsten, on the other hand, isn’t a good catalyst because it adsorbs too strongly

Question 11

platinum and nickel make good catalysts

Answer 11

adsorb strongly enough to hold and activate the reactants, but not so strongly that the products can’t break away

Question 12

Autocatalysis

Answer 12

reaction is catalysed by one of its products

Question 13

Autocatalysis example

Answer 13

oxidation of a solution of ethanedioic acid (oxalic acid) by an acidified solution of potassium manganate(VII) (potassium permanganate)