Practical 2

• Write a method to determine the enthalpy of combustion of a fuel

  1. Measure 100 cm3 of water into a calorimeter which is the same as 100g of water
  2. Weigh a spirit burner containing the liquid to be burnt
  3. Measure the initial temperature of the water using a thermometer
  4. Use the spirit burner to heat the water
  5. Stop heating when there is a reasonable temperature rise, stir and measure the final temperature
  6. Reweigh the spirit burner and calculate the mass of fuel used in the burner by subtraction
• Write a method to determine the tnhalpy change of neutralisation

  1. Place a polystyrene cup in a glass beaker for insulation + support
  2. Rinse volumetric pipette with acid and then transfer 25 cm3 of acid into cup
  3. Stir the acid with a a thermometer and record the temperature every minute for 3 minutes
  4. Rinse a second volumetric pipette with base and then measure out 25 cm3 of base
  5. Add base to the acid at 4th minute, stir and record temperature every minute for several minutes
• If a reaction is slow and the exact temperature rise can be difficult to obtain how can this be calculated?

  Take temperature readings at regular intervals

  Plot a graph with temperature (y axis) against time (x axis)

  Extrapolate the temperature curve/line back to the time the reagents were added together
• Suggest why the value measured in a combustion experiment is less exothermic than the data book value

  Incomplete combustion

  Heat loss to surroundings/apparatus

  Evaporation of fuel