Specific Latent Heat

Created by: theninjaemu
Created on: 11-07-17 09:35

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Specific Latent Heat
- Defining SLH
  - The energy required to change the phase per unit mass while at a constant temperature
  - L = E/m
    - E is energy transferred
    - m is the mass
  - When the substance changes from solid to liquid phase, this is the SLH of fusion
  - When the substance changes from liquid to gas phase, this is the SLH of vaporisation
- SLH of fusion
  - When a substance is at its melting point, energy is required to change phase to a liquid
  - The energy transferred increases the internal energy, without increasing the temperature of the substance
  - A circuit can be used to determine SLH of fusion
    - Ammeter connected in series
    - Voltmeter connected in parallel with a heater
    - Variable resistor used to control current
  - A thermometer is used to ensure the ice is at its melting point. The ice should just be starting to melt when the heater is switched on
  - The energy transferred is current x p.d. x time
  - The mass is the mass of ice melted, calculating by subtracting the mass of an empty beaker from a beaker with melted ice in it
- SLH of vaporisation
  - Energy required for SLH of vaporisation is usually considerably more than SLH of fusion
  - To determine SLH of vaporisation, a heater can be used with a condenser to collect and measure the mass of liquid that changes phase
  - SLH of vaporisation can be found using L = (IVt)/m
  - m is the mass of water that changes phase during heating
- Combining SLH and SHC
  - Considering both SHC and SLH, you can determine the total energy required to heat and then change the phase of a substance
  - Heating a solid to a melting point (E = m x c of solid x temp. change)
  - Melting solid at constant temperature (E = m x SLH(f))
  - Heating liquid to its boiling boint (E = m x c of liquid x temp. change)
  - Boiling the liquid at constant temperature (E = m x SLH(v))
  - The total energy is determined by adding up all the energy transferred in each section