PHYSICS - PROPERTIES OF MATTER - Specific latent heat

change if state

physical change where a substance changes from 1 state to another without a change in chemical composition

During change of state:

Temperature remains constant

energy is either absorbed or released

energy is used to break or form intermolecular bonds, not increase kinetic energy

melting

solid to liquid

freezing

liquid to solid

evaporation

liquid to gas

condensation

gas to liquid

sublimation

solid to gas

specific latent heat (L)

amount of heat energy required to change the state of 1kg of a substance without change of temperature

J/kg

specific latent heat if fusion (Lf)

energy required to change 1kg if a substance from solid to liquid at a constant temperature

specific latent heat of vapourisation (Lv)

energy required to change 1kg of a substance from liquid to gas at a constant temperature

formula of SLH

E = mL

no temperature change when heat energy is added or removed during state change

temperature remains constant until change is complete

energy is used to overcome forces of attraction between particles in a substance

different substances have different Lf and Lv

substances with strong intermolecular forces have higher L as more energy is required to change their state

energy conservation

total energy gained by another substance = total energy lost by another substance

practical applications of SLH

melting and freezing - ice absorbs a lot of energy as it melts without changing temperature, useful of cooling drinks and preserving food

boiling and condensation - steam releases a lot of energy when it condenses, steam burns more severe than burns from water

refrigeration - fridges remove heat from food using SLH, refrigerants absorb heat during evaporation and release it during condensation

cooling curve

a graph that shows how the temperature of a substance changes over time as it loses heat

used to analyse the cooling and phase changes of a substance

key features of a cooling curve

cooling in gas phase - temperature of gas decreases as it loses heat, particles lose kinetic energy, resulting in reduced temperature

condensation - during condensation, temperature remains constant even though heat is beung released, as energy is being used to form intermolecular bonds as gas becomes liquid

cooling in liquid phase - temperature of liquid decreases as it loses heat, particles move slower as their kinetic energy decreases

freezing - energy used to form stronger intermolecular bonds as liquid becomes solid

cooling in solid phase - temperature of solid decreases as it loses heat, particles vibrate less as their kinetic energy decreases

cooling curve interpretation

flat sections represent state changes

sloped sections represent temperature changes

SLH and cooling curves

flat sections of curve represent energy involved in a change of state

latent heat of fusion - occurs during freezing

latent heat of vapourisation - occurs during condensation