C2bL6 Catalysts

Key Words

Acid Rain - rain into which an acid gas has dissolved to make an acid

Adsorb - to collect a gas on a surface (NOT absorb).

Ammonia - NH₃, a pungent and toxic gas.

Contact Process - industrial process to make sulphur trioxide and sulphuric acid.

Desorbed - remove the gas from a surface.

Enzymes - catalysts produced by living organisms.

Haber process - industrial process to make ammonia.

Grade E

All cars have to have catalytic converters

carbon monoxide + nitrogen dioxide  ®  carbon dioxide  + nitrogen

4CO _(g) + 2NO_{2 (g)} ® 4CO_{2 (g)} + N_{2 (g)}

Nitrogen dioxide reacts with water to give nitric acid, making acid rain.  Carbon monoxide is a poisonous gas.

Without a catalyst, the reaction does not happen.

Hydrogen peroxide slowly breaks down to form water and oxygen.

hydrogen peroxide ® water + oxygen

2H₂O_{2 (aq)} ® H₂O _(l) + O_{2 (g)}

The reaction occurs much faster of manganese oxide (MnO₂) is added.  The same is seen if you drop a piece of liver into the hydrogen peroxide.  This is due to an enzyme called catalase.

Grade C

You can weigh the manganese oxide, do the reaction with hydrogen peroxide, filter it off, and weigh it again.  You will find that the mass before and after are the same.  The catalyst is not used up in the reaction

You can try other transition metal catalysts to see how the rate of reaction is changed.  Even if the rate of reaction is even quicker, the same amount of hydrogen is always the same.

Catalysts will not only speed up a reaction, they also can make reactions happen that will not occur in normal conditions:

• The Contact Process used in the manufacture of sulphuric acid uses vanadium pentoxide (V₂O₅).
• The Haber Process uses iron as a catalyst to make ammonia from nitrogen and hydrogen;
• Nickel catalyses reactions that convert vegetable oils to margarine.

Grade A

The catalyst in a car adsorbs gas onto the surface and stretches the bonds, making it easier for a reaction to happen.  Then the gases are desorbed to go up the exhaust.  The catalyst is a very expensive metal, platinum.

  Adsorbing is NOT the same as absorbing.

Petrol used to have tetraethyl lead as an anti-knock agent.  It did its job really well, but large amounts of lead in the environment is not a good idea, so leaded petrol was banned in new cars.  It was available for really old cars.  However if you put leaded petrol into a car with a catalytic converter, the lead would coat the metal, wrecking the catalyst.  The catalyst was poisoned.  You can do similar damage if you put diesel into a petrol car by mistake.  (In the old days, you would only have to get rid of the diesel fuel and put in petrol.  The engine would smoke a bit, but it would be OK in the end.  Nowadays you can do very expensive damage to all the sophisticated control equipment.  So don't.)

Enzymes are catalysts that make biological reactions happen.  They make the difficult reactions in living things go.  They are very complex, and work best at 37 ^oC.  Anything above 40 ^oC will cause enzymes to denature, ruining their catalytic action