Chemistry

• The rate of a reaction is a measurement of how quickly reactants get used up or products are made
• To calculate the mean rate of a reaction


  1. Take the quantity of reactant used divided by the time it took

  2. Take the quantity of product made divided by the time taken
• Quantity of reactant or product

  Can be measured in grams as a mass or in cm^3 as a volume
• Steep curve of amount of substance against time

  Indicates a high rate of reaction
• Shallow curve of amount of substance against time

  Indicates a low rate of reaction
• Experimental methods to determine rate of reaction

  1. Measure change in mass using balance and stopwatch

  2. Measure volume of gas produced using syringe/measuring cylinder and stopwatch
• To calculate mean rate of reaction from a graph

  1. Find amount of substance at each time

  2. Find change in amount

  3. Find change in time

  4. Calculate mean rate = change in amount / change in time
• Factors affecting rate of reaction

  • Temperature
  • Pressure
  • Concentration
  • Surface area
  • Catalysts
• Collision theory


  Chemical reactions can only occur when reactant particles collide with each other with sufficient energy
• Increasing temperature


  Increases rate of reaction
• Increasing pressure


  Increases rate of reaction
• Increasing concentration


  Increases rate of reaction
• Increasing surface area


  Increases rate of reaction
• Catalyst


  Substance that can speed up rate of reaction without being consumed, by providing alternative pathway with lower activation energy
• Reversible reactions are shown using the symbol ⇌
• Reversible reaction


  Products can react to form original reactants
• Endothermic reaction in one direction


  Exothermic in opposite direction, with equal energy transfer
• Equilibrium


  In a reversible reaction, forward and backward reactions happening at same rate
• Crude oil is a finite resource composed of remains of ancient biomass
• Hydrocarbon


  Molecule made up of carbon and hydrogen only
• Examples of homologous series

  • Alkanes
  • Alkenes
  • Alcohols
  • Carboxylic acids
• Properties of homologous series

  • Same general formula
  • Molecular formula differs by CH2
  • Similar chemical properties
  • Gradual change in physical properties
• First 4 alkanes


  • Methane
  • Ethane
  • Propane
  • Butane
• Crude oil is a mixture of different hydrocarbons of varying length
• Names of the first four members of the alkane homologous series

  • Methane
  • Ethane
  • Propane
  • Butane
• Alkanes


  • All names end in 'ane'
  • Beginning of names follow the pattern: meth, eth, prop, but
• Monkeys eat peanut butter


  Helps remember the correct order of the first four alkanes: meth, eth, prop, but
• Formulas of the first four alkanes

  • Methane: CH4
  • Ethane: C2H6
  • Propane: C3H8
  • Butane: C4H10
• The formulas of alkanes follow the general formula CnH2n+2
• Crude oil


  A mixture of different hydrocarbons of different lengths
• Fractional distillation of crude oil

  1. Crude oil passes into a furnace and gets heated and vaporized

  2. Vapour passes into a fractionating column

  3. Vapour cools as it rises up the column

  4. Hydrocarbons condense at different heights based on boiling points

  5. Different fractions are collected at different heights
• Products obtained from fractional distillation of crude oil

  • Fuels (e.g. petrol, diesel oil)
  • Feedstock for petrochemical industry (e.g. solvents, polymers, detergents, lubricants)
• Hydrocarbons


  • As the molecules get larger, the boiling points increase, the viscosity increases, but the flammability decreases
• Combustion of hydrocarbons


  Hydrocarbon + Oxygen → Carbon dioxide + Water
• The general formula for complete combustion of a hydrocarbon is CxHy + (x+y/4)O2 → xCO2 + y/2 H2O
• Example balanced equation for combustion of methane: CH4 + 2O2 → CO2 + 2H2O
• Cracking


  Process to break down longer hydrocarbons into shorter, more useful hydrocarbons
• Cracking process


  Longer hydrocarbon → Shorter alkane + Alkene
• Cracking methods


  • Catalytic cracking
  • Steam cracking
• Alkenes


  More reactive than alkanes, can react with bromine water to decolorize it (become colorless)