chem

• Rate of reaction


  The quantity of product formed over time

  or

  The quantity of reactant used up over time
• Unit for rate of reaction

  cm^3/s

  or

  g/s

  or

  moles/s (HT only)
• Equation for mean rate of reaction


  quantity of reactant used ÷ time taken

  or

  quantity of product formed ÷ time taken

  
• Factors affecting rate of reaction (5)

  Concentration of reactants in solution

  Pressure of reacting gases

  Surface area of solid reactants

  Temperature

  Presence of a catalyst
• Collision theory


  For a reaction to occur, particles must collide with each other with sufficient energy
• Activation energy


  The minimum amount of energy that particles must have to react
• Using collision theory, why does increasing concentration of reactant in solutions increase rate of reaction?

  Increases the frequency of collisions as there are more particles to collide with each other.
• Using collision theory, why does increasing surface area of solid reactants increase rate of reaction?

  Increases the frequency of collisions as there are more particles exposed on the surface of the solids to collide with each other.
• Using collision theory, why does increasing pressure of gas reactants increase rate of reaction?

  Increases the frequency of collisions as the particles are more tightly packed.
• Using collision theory, why does increasing temperature of particles increase rate of reaction?

  Increases the frequency of collisions and makes the collisions more energetic so more likely to have more successful collisions.
• Catalyst


  Substance that speeds up the rate of a chemical reaction by lowering the activation energy. It is not used up in the reaction so can be reused.
• Using collision theory, why does adding a catalyst increase rate of reaction?

  Catalysts lower the activation energy required to have a successful collision, so therefore there are more successful collisions
• Reversible reaction


  A chemical reaction in which the products react to re-form the original reactants

  
• Equilibrium


  When a reversible reaction occurs in a closed system (the products and reactants can't escape) an equilibrium is reached where the forward and backward reaction occur at exactly the same rate.

  
  

  This would mean the concentrations of the reactants and products would be constant at equilibrium
• Crude oil


  Remains of ancient biomass consisting of mainly plankton that was buried in the mud millions of years ago.

  
  

  It is a mixture of a very large number if hydrocarbon compounds
• Hydrocarbon


  A molecule consisting of only hydrogen and carbon
• Alkanes


  The homologous series with the general formula: C(n)H(2n+2).

  
  

  They are all single carbon-carbon bonds
• Methane


  CH4

  
• Ethane


  C2H6

  
• Propane


  C3H8

  
• Butane


  C4H10

  
• What is fractional distillation


  Separating the many hydrocarbons in crude oil into fractions which all contain molecules with similar numbers of carbon atoms.
• How does fractional distillation work?

  Crude oil heated up and evaporated.

  Vapour pumped into fractional distillation column.

  Vapour rises up column where it becomes temperature drops higher in the column

  Fractions condense at different levels depending on their boiling point.

  
• How does length of hydrocarbon affect boiling point?

  The longer the hydrocarbon the higher the boiling point
• How does length of hydrocarbon affect viscosity?

  The longer the hydrocarbon the more viscous
• How does length of the hydrocarbon affect flammability?

  The longer the hydrocarbon the more flammable
• Cracking


  Breaking down longer hydrocarbons into shorter more useful ones
• Conditions for cracking


  High temperature and a catalyst
• Products of cracking


  An alkane and an alkene
• Alkene


  The homologous series with the general formula C(n)H(2n).

  
  

  These have one carbon-carbon double bond

  
• Test for alkenes


  Turn orange bromine water colourless.
• C10H22 --> C4H10 + ???


  C6H12
• Pure substance


  A single element or compound, not mixed with any other substance. Has a specific melting and boiling point.
• Formulation


  A mixture that has been designed as a useful product.

  
  

  Made by mixing components in carefully measured quantities for consistency
• Examples of formulation


  Fuel, cleaning agents, paints, medicines, alloys, fertilisers and foods
• What is chromatography?


  Method to separate mixtures based on how soluble they are in a solvent
• How to carry out chromatography

  Draw a pencil line near to bottom

  Place ink sample(s) on the pencil line

  Place bottom of paper in solvent (water) so solvent level is under pencil line

  Allow solvent to run up the paper

  Take paper out of solvent before solvent front reaches the top of the paper
• Equation for Rf value


  Distance moved by substance / distance moved by solvent.

  
  

  Always a number between 0 and 1
• How to chromatography results

  Either run sample against known chemicals and compare heights travelled and colours. Those with same height and colour are same chemical.

  
  

  Or calculate Rf value and compare this to database
• Test for hydrogen


  Squeaky pop when lit splint placed in hydrogen