cheMistry~

by - 10:38 AM

Other processes and reactions
This means to coat iron or steel with a layer of zinc to stop it rusting (more details on Metal Reactivity page)
The synthesis of ammonia by combining nitrogen and hydrogen using high temperature, pressure and an iron catalyst. (all the details)
Contact Process
  • Part of the manufacture of sulphuric acid from: (all the details)
  • sulphur ==> sulphur dioxide ==V catalyst==> sulphur trioxide* ==> sulphuric acid.
  • S(s) + O2 (g) ==> SO2 (g), * 2SO2 (g) + O2 (g) ==> 2SO3 (g),
  • followed by, indirectly, SO3 + H2O ==> H2SO4
Double decomposition Double decomposition is chemical reaction that takes place between two compounds, in which the first part of one compound combines with the second part of another compound. The bits left over combine to form the second compound. One of the compounds is usually insoluble.
  • e.g. if you mix solutions of sodium chromate with lead nitrate you get a yellow precipitate of lead chromate and sodium nitrate is left in solution.
  • sodium chromate + lead nitrate ==> lead chromate + sodium nitrate
  • Na2CrO4(aq) + Pb(NO3)2(aq) ==> PbCrO4(s) + 2NaNO3(aq)
  • This is the yellow pigment Van Gogh used in his paintings and you see it as the road markings you don't park on!
Catalytic Conversion (car exhaust)
  • One way of reducing pollutants from a car exhaust is to use transition metal catalysts (Pt+Rh set on a heat resistant base = the catalytic converter). A platinum/rhodium catalyst converts toxic carbon monoxide and nitrogen monoxide gases into harmless carbon dioxide and nitrogen gases.
  • 2CO (g) + 2NO (g) == Pt/Rh ==> 2CO2 (g) + N2 (g)
Esterification
  • Combining an organic carboxylic acid with an alcohol, produces an pleasant smelling ester (which are used in perfumes and flavourings) and water.
    • e.g. ethanoic acid + ethanol (c) doc b ethyl ethanoate + water
    • ethanoic acid (c) doc b + ethanol (c) doc b the ester ethyl ethanoate (c) doc b + H2O
    • Its an equilibrium, 2/3 rds conversion, and the reaction is catalysed by a few drops of concentrated sulphuric acid.
Rusting
  • Iron (or steel) corrodes more quickly than most other transition metals and readily does so in the presence of both oxygen (in air) and water to form an iron oxide. This means rusting is an oxidation reaction.
  • iron + oxygen + water ==> hydrated iron(III) oxide
  • 4Fe(s) + 3O2(g) + xH2O(l) ==> 2Fe2O3.xH2O(s)
  • i.e. rust is an orange-brown solid of hydrated iron(III) oxide formed from the reaction with oxygen and water (the equation is not meant to be balanced and the amount of water x is variable, from dry to soggy!).
  • For more details of the chemistry of rusting and its prevention go to the corrosion section on the Metal Reactivity Series page.
Substitution
  • A substitution reaction is where one part of a molecule is replaced by something else.
  • e.g. when chlorine reacts with methane, a hydrogen atom in methane is replaced by a chlorine atom from the chlorine molecule.
  • methane + chlorine ==> chloromethane + hydrogen chloride
  • CH4 + Cl2 ==> CH3Cl + HCl
Addition
  • An addition reaction is when one molecule adds to another molecule resulting in a single product e.g.
  • ethene + bromine ==> 1,2-dibromoethane
  • C2H4 + Br2 ==> C2H4Br2
  • ethene doc b oil notes bromine doc b oil notes 1,2-dibromoethane

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