catalysts

homogeneous catalysts are

in the same phase as the reactants

heterogeneous catalysts are

in different phase to reactants

examples of heterogeneous catalysts is

in the haber process, in catalytic converters

heterogeneous catalysts are used in the haber process because

a solid iron catalyst is used to speed up the reaction between hydrogen and nitrogen gases

transition metals make good catalysts because

they have variable oxidation states and electrons are transferred to produce a reactive intermediate and speed up the reaction rate

catalysts effect on equilibrium is

no effect, but effects the rate at which equilibrium is attained

benefits of catalysts

they allow reactions to take place at lower temperatures, enable different reactions to be used, are often enzymes, great economic importance, can reduce pollution

catalysts allow reactions to take place at lower temperatures which

saves energy and reduced co2 output

catalysts enable different reaction to be used

which reduces waste can cause better atom economy

catalysts are often enzymes so

they generate specific products and operate effectively at room temperatures

heterogeneous catalysis takes place

at active sites on the surface of a solid and gases are adsorbed onto the surface and form weak bonds between the gas and metal atoms

the stages of heterogeneous catalysis are

adsorption, reaction, desorption

adsorption stage is

the formation of bonds with surface weakens bonds in gas molecules making subsequent reaction easier

reaction stage is

adsorbed gases may be held on the surface which increases chances of favourable collisions

desorption stage is

the products are then released from the active sites

the strength of adsorption is critical because it can be

too weak which means there is little adsorption so molecules will not bond to the surface, too strong so molecules are held tightly an remain on the surface thus blocking reactive sites an preventing further reaction, just right where reactants are attracted yet products can leave to open up active sites

heterogenous catalysis can increase the ROR as

one species is adsorbed onto the surface so is more likely to undergo a collision, one species is held in a favourable position or reaction to occur, adsorption onto the surface allows bonds to break and fragments to react quicker, two reactants are adsorbed alongside each other gives a greater concentration

heterogeneous catalysts come in the form of

finely divided and mounted in a support medium to increase the surface area providing more collision sites and maximising the surface area to reduce costs

homogeneous catalysis reaction proceeds through

an intermediate species with lower energy, there is usually more than one reaction step and transition metal ions are often involved

examples of homogeneous catalysis is

in acids like the hydrolysis of esters, in gases like in the ozone layer