6.4 States of Matter & Changes of StateThe three states of matter are: solid, liquid, gas. A change of state requires a change in the thermal energy of a substance.

6.4 States of Matter & Changes of StateThe changes in temperature that occur when a substance absorbs & releases thermal energy can be shown in the heating and cooling graphs below:

6.4 States of Matter & Changes of StateNotice the key aspects of each graph:• Temperature changes occur only when one state is present, represented by the

angled parts of the graph.• Temperature remains constant during a change of state, represented by the flat

parts of the graph. Absorbed or released thermal energy is being transformed into potential energy, rather than kinetic energy.

During melting or boiling, thermal energy absorbed by the particles of a substance is needed to break the bonds that hold them together.During condensation or freezing, thermal energy released by the particles allows them to move closer together rand become more organized.

6.4 Latent HeatLatent Heat (Q) is the total thermal energy absorbed or released by a substance during a change of state; measure in Joules (J).Latent means ‘hidden’ because there is no measurable change in temperature.

Latent Heat of Fusion is the amount of thermal energy required to change a solid into a liquid or a liquid into a solid; solid ↔ liquid.Latent Heat of Vaporization is the amount of thermal energy required to change a liquid into a gas or a gas into a liquid; liquid ↔ gas.

Specific Latent Heat (L) is the amount of thermal energy required for 1 kg of a substance to change from one state into another; SI units: (J/kg)

6.4 Specific Latent Heat

Specific Latent Heat of Fusion (Lf) is the amount of thermal energy required to melt or freeze 1 kg of a substance to change from one state into another; SI units: (J/kg)

Specific Latent Heat of Vaporization (Lv) is the amount of thermal energy required to boil or condense 1 kg of a substance to change from one state into another; SI units: (J/kg)

To calculate the latent heat (Q) during a change of state:

SI units: Q ⤍ J; m ⤍ kg; Lf and Lv ⤍ (J/kg)

6.4 States of Matter & Changes of StateEvery substance has a different specific latent heat because every substance is composed of different particles.

SP #1,2 p.292-293

6.4 Homework

Practice # 1-3 p.293Questions # 1, 3, 5-8 p.295