measuring changes in chemical reactions

• what is hess' law?

  that the amount of heat involved in producing one chemical from another is always the same, no matter how many stages are taken to obtain the desired product.
• what is SLC?

  24.8
• what is butane?

  C4H10
• what is oxygen?


  O2
• what is methane?

  CH4
• what do complete combustion equations produce?

  carbon dioxide and water
• what is ethanol?

  C2H5OH
• what can a solution calorimeter be used for?

  Measuring heat changes during chemical reactions.
• what are the steps to experimental determination?

  1. measure the volume of H2O and measure the initial temperature of H2O
  2. measure the mass of spirit burner and fuel or the mass of food and holder.
  3. light the burner or food and heat
  4. extinguish burner and record highest temperature reached by water
  5. measure the mass of the burner and the remainder fuel
• what is the specific heat capacity of water?

  4.186 J/g°C
• what is calorimetry? measuring the heat energy released by a substance when it is heated
• how to prevent heat loss?

  • place lid on calorimeter
  • insulating beaker of water
  • placing insulation around burning food
• what is a calibration factor?

  A calibration factor is a constant value used to adjust measurements or readings to account for systematic errors or variations in a measuring instrument.
• what units does a calibration factor use?


  Joules of degrees
• once a CF is known what is it known as?

  its known as 'calibrated'
• how can a calorimeter become calibrated?

  By using a known heat source or a substance with a known heat capacity to determine the calorimeter's response to heat.
• energy changes that occur in reactions can be measured with a?

  solution calirometer
• why is styrofoam used in solution calorimetry?

  Insulation and helps minimise heat loss.
• what does exothermic mean?

  Releasing heat.
• what does endothermic mean?

  Absorbing heat.
• what is Solution calorimetry?

  Measurement of heat released or absorbed during a chemical reaction.
• Solution calorimetry can not be measured when?

  gases are produced.
• why is it important to calibrate a calorimeter?

  Calibrating a calorimeter accounts for any heat loss, meaning that the calorimeter does not need to be perfectly insulated. This improves the accuracy of results.
• a complete combustion always involves?

  a fuel reacting with oxygen gas to produce carbon dioxide and water
• Percentage energy efficiency for combustion is the percentage of?

  chemical energy converted to useful energy.
• what are the 3 main greenhouse gases?

  H2O (water vapour), CO2 (carbon dioxide), and CH4 (methane)
• what is the most potent green house gas?

  water vapour
• how much energy does fibre provide?

  none
• SOLUTION calimetry is used for?

  precipitation reactions (all liquid products)
• Percentage energy efficiency for combustion is the percentage of chemical energy converted to useful energy
• Greenhouse gases

  Gases that contribute to the enhanced greenhouse effect by absorbing and emitting infrared radiation from the sun
• Molar heat of combustion

  Amount of heat, in kJ mol−1, released when 1 mole of substance completely combusts in excess oxygen gas
• Molar volume of gases (Vm)

  Volume occupied by one mole of an ideal gas at a given temperature and pressure
• Standard laboratory conditions (SLC)

  Set of conditions used as a standard, involving a temperature of 25 °C (298 K) and a pressure of 100 kPa
• Stoichiometry

  The relationship between relative quantities of reactants and products in a chemical reaction
• Mass to mass calculations involving combustion

  1. Convert known substance mass to an amount (in mol)

  2. Multiply the number of moles of the known substance by the stoichiometric ratio from the balanced (thermo)chemical equation to determine the number of moles of the unknown substance

  3. Convert the number of moles of the unknown substance to a mass
• Mass to volume calculations involving combustion

  1. Convert known substance mass to an amount (in mol)

  2. Use the formula n = V/Vm to convert moles to volume at SLC
• Calculating the quantity of greenhouse gases produced by combustion reactions

  1. Calculate the total mass or volume of greenhouse gases produced

  2. Use the formula: Net amount = amount produced - amount consumed
• At SLC (298 K or 25 °C), water is always a liquid
• Methane is ten times more potent (strong) as a greenhouse gas than carbon dioxide

  The combustion of methane to produce carbon dioxide can be a 'net-green' process if the alternative is the release of methane into the atmosphere