Measurement of the specific latent heat of vaporisation of water

When steam, at 100 degrees celcius, is bubbled into water, it first condenses to water and then its temperature decreases as it gives heat to the water. If this occurs in an insulated container then the heat lost by the steam is equal to the heat gained by the container and the water. The specific latent heat of vaporisation of water (l) can then be calculated using the formula:

ms l + ms cw (fall in temp of condensed steam) = mc cc (rise in temp of calorimeter) + mw cw (rise in temp of water)

where ms, mc and mw are the masses of steam, calorimeter and water respectively and cw and cc are the specific heat capacities of water and of the material of the calorimeter. Note: ccopper = 390 J / kg / K, cAluminium = 910 J / kg / K

Procedure:

  1. Press "Copper" of "Aluminium" for the calorimeter
  2. Using the mouse, drag the calorimeter on to the top- pan balance
  3. Press "Find Mass". Record mc
  4. Press "Add Water". A random mass of water between 50 and 80g is added.
  5. Press "Find Mass". Record value and find mw
  6. Drag the calorimeter into the insulated container
  7. Press "Thermometer In". Record starting temperature
  8. Press "Add Steam". Steam is added until a random rise in temp between 10 and 18 degrees occurs. Record the highest temp. reached after the steam tube has been removed
  9. Press "Remove Thermometer"
  10. Drag the calorimeter to the balance
  11. Press "Find Mass". Subtract to find ms

Analysis:

Using the formula given above, calculate the specific latent heat of vaporisation of water.

To repeat the experiment press "Reset" and follow steps 1 to 11 above

Precautions:

  • Ensure that only steam (not water) enters the water in the calorimeter. Use a "steam trap" (it actually traps water) if available
  • Use cooled water (about 5 deg. below room temp.) at the start of the experiment so that, on average, heat is neither lost or gained from the surroundings.
  • Use a well insulated calorimeter to avoid loss or gain of heat to the surroundings
  • Stir well and record the highest temperature when the steam has stopped bubbling in to the water