2 - MEASURING ENTHALPY CHANGE

• ENTHALPY CHANGE OF COMBUSTION METHOD?

  1. Add fuel to spirit burner and record initial mass
  2. Add known volume of water to calorimeter
  3. Clamp in position above spirit burner
  4. Use thermometer to measure initial temperature of water
  5. Use spirit burner to heat water in calorimeter to 40 degrees Celsius
  6. Record temperature change
  7. Reweigh spirit burner
  8. Calculate change in mass of fuel
  9. Calculate energy release q = mcT
  10. Calculate enthalpy change H = q / (n x 1000)
• LOWER EXPERIMENTAL VALUE OVER QUOTED VALUE?

  • heat loss
  • incomplete combustion
  • evaporation of fuel from spirit burner
  • not under standard conditions
• HOW TO MINIMISE HEAT LOSS?

  • reduce distance between flame and beaker/ calorimeter
  • protective sleeve around flame
  • lid on beaker/ calorimeter
• ENTHALPY CHANGE OF REACTION METHOD?

  1. Add x g of water to polystyrene cup
  2. Record initial temperature using thermometer every minute for 3 minutes
  3. Add x g of solid NaOH to cup
  4. Record temperature using thermometer every minute, starting at 5 minutes
  5. Plot graph of temperature (y-axis) versus time (x-axis)
  6. Extrapolate to time of mixing
  7. Calculate temperature change
  8. Calculate H = mcT/ n x 1000