UNIT NINE: THERMAL PROPERTIES OF MATTER

NINE.ONE: Temperature and Internal Energy

what is internal energy?

It is the total energy of the particles in the matter.
It comprises of 2 components: kinetic and potential energy
An increase in temperature leads to an increase in the kinetic component of the internal energy.

NINE.TWO: Melting And Solidification

Melting is he change of state from solid to liquid, without a change in temperature.
Solids melt when the strong intermolecular bonds are broken.
Since energy is needed to break the bond, thermal energy is used to do the work.
Once, the bonds are broken, they are free to move out of their fixed positions.
During melting, the temperature remains constant at the melting point and thermal energy is absorbed by the substance.

Eg: solid ice melting to become liquid water.

The reverse process of melting is solidification, from liquid to solid, without the change in temperature.
The temperature remains constant at the freezing point and thermal energy is released by the substance.

NINE.THREE: Boiling And Condensation

Boiling is the change of state from a liquid into vapour, occurring at a constant temperature called the boiling point.
During boiling the temperature remains constant at its boiling point and thermal energy is being absorbed by the substance.

Condensation on the other hand is the process whereby vapour changes into liquid at the same constant temperature and heat is given out.
During this process, the temperature remains constant at the condensation point and thermal energy is released.

NINE.FOUR: Evaporation

Evaporation like boiling is the change of state from liquid to gas.
The evaporation of liquid is due to molecules at the surface with energy greater than the average kinetic energy escaping from the rest of the liquid.
However, the difference between evaporation and boiling is that evaporation can occur at any temperature.

Boiling	Evaporation
1) Occurs at fixed temperature 2) Quick process 3) Takes place throughout the liquid 4) Bubbles are formed in liquid 5) Temperature remains constant 6) Thermal energy supplied by energy source	1) Occurs at any temperature 2) Slow process 3) Takes place only at the liquid surface 4) No bubbles formed in liquid 5) Temperature may change 6) Thermal energy supplied by surroundings

Factors affecting the rate of evaporation:
-temperature
-humidity of surrounding air
-surface are of liquid
-movement of air
-pressure
-boiling point of the liquid

Here's a video on condesation and evaporation.