# Specific Latent Heat

• 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