AQA Chem 1 - Essential Cramming Cards

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  • Created by: Anna
  • Created on: 14-05-12 23:11

Relative Mass

Relative atomic mass =                 average mass of an atom

                                               1/12th mass of 1 atom of 12-Carbon

Relative formula mass =                average mass of an entity

                                                1/12th mass of 1 atom of 12-Carbon

Relative molecular mass =           average mass of a molecule

                                                1/12th mass of 1 atom of 12-Carbon

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Economy & Yield

% Atom economy = 100 x    mass of desired product

                                             total mass of reactants

Yield = 100% x         number of moles of a specified product

                           theoretical maximum numer of moles of product

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Number of Moles

Number of moles =         mass in g        

                               mass of 1 mole in g

Number of moles in solution = Mass x Volume

                                                     1000

Concentration =  numer of moles

                           volume in dm3

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Ideal gas equation

PV = nRT

V = nRT

      P

P = nRT

      V

n = PV

      RT

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Combustion

Complete:

CH4 + 2O2  --> CO2  + 2H2O

Incomplete (lack of oxygen):

C3H8 + 31/2O2 --> 3CO  +  4H2O

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Polluntants

Carbon Monoxide, CO 

  • posionous gas formed by incomplete combustion

Nitrogen Oxides, NO NO2 N2O4

  • Produced when there is enough energy for N2 and O2 to combine
  • Occurs in a petrol engine (high temp when spark lights fuel)
  • Contributes to photochemical smog and acid rain

Sulfur Dioxide, SO2

  • Contributes to acid rain, produced from sulphur impurities in crude oil

Water Vapour, unburnt hydrocarbons and CO2

  • Greenhouse gases that contribute to the warming of the earth
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Pollutants - Equations

Nitrogen Oxides:

N2 + O2 --> 2NO

Sulfur dioxide:

SO2 + H2O --> H2SO3 + 1/2O2 --> H2SO4

Removing sulfur:

  • Use Calcium Oxide (CaO) or limstone (CaO3) in flues to absorb sulfur
  • Greates gypsum (CaSO4) which is used in plaster - flue gas desulfurisation
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Catalytic Convertors

Catalytic Convertors:

  • all new cars equipped with a catalytic convertor in exhaust system
  • reduces output of nitrogen oxides, unburnt hydrocarbons and CO
  • ceramic honeycomb (greater surface area) coated in platinum and rhodium metals
  • polluting gases pass over catalyst to form less harmful products:

1. 2CO  +  2NO  --> N2 + 2CO2

2. hydrocarbon + nitrogen oxide --> nitrogen + carbon dioxide + water

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Cracking

Cracking has two purposes:

  • Creates shorter, more useful chains e.g. petrol
  • Some products are alkenes, more reactive than alkanes

Thermal Cracking:

  • done under high pressure and high temperature
  • briefly forms free radicals
  • one product is always an alkene

Catalytic Cracking:

  • lower temperature and pressure than thermal cracking
  • uses a zeolite catalyst - silicon dioxide and aluminium oxide (acidic)
  • mainly used to produce motor fuels
  • products include branched alkanes, cycloalkanes and aromatic compounds
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