BRENDA'S PHYSICS BLOG

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2008-09-04T10:50:00.000-07:00

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2008-09-04T09:44:00.000-07:00

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.

2008-09-04T08:20:00.000-07:00

UNIT EIGHT: TRANSFER OF THERMAL ENERGY

EIGHT.ONE: Transfer Of Thermal Energy

What causes transfer of thermal energy?

3 small basins of water labelled A,B & C at 10degrees, 37degrees and 60degrees respectively
Your right hand feels cold when you immerse it in A.
Your left hand feels warm in C.
However when you immerse your hands in B, you will feel neither hot nor cold.
the water in B is the same temperature as your hands, therefore, there is thermal equilibrium.
There is no net gain or loss in temperature betweeen the water in B and your hands. Hence, you will feel neither hot nor cold.

thermal energy is transferred only when there is a difference in temperature
it always flows from a region of higher temperature to a region of lower temperature

How is thermal energy tramsferred?

Thermal energy is transferred through 3 processes: conduction, convection and radiation.

1)Conduction is the process of thermal energy transfer without any flow of material medium.
The two main mechanism for conduction are atomic or molecular (non-matals & metals) and free electron diffusion(for metals only).
Liquid and gases are poor conductors of heat compared to solid.
Here's a video about conduction.

2)Convection is the transfer of thermal energy by means of currents in fluid (liquids or gases)
It is the movement of fluid caused by the change in density in various parts of the fluid.

Here's video about convection.

3)Radiation is the continual emission of infared waves from the surface of all bodies, transmetted without the aid of a medium. It does not require a medium for thermal transfer.
Factors affection rate of infared radiation:
-colour and texture of surface
eg: dull, black shiny surfaces are better absorbers and emitters of infared radiation than shiny, white surfaces.
-surface temperature
-surface area

Here's a video on radiation.

EIGHT.TWO: Application of thermal energy transfer

Uses of good conductor of heat:
-cooking utensils like kettles and boilers
-soldering iron rods
-heat exchangers

Uses of bad conductor of heat:
-handles of appliaces and untensils like kettles and boilers
-table mats
-sawdust
-wooden ladles
-woollen clothes

Common applications of convection:
-electric kettles
-household hot water system
-air conditioners
-refrigerator

Common applications of radiation:
-teapots
-the greenhouse
-vacuum flasks

2008-09-04T07:21:00.000-07:00

UNIT SEVEN: Kinetic Model Of Matter

SEVEN.ONE: The States Of Matter

There are 3 types of matter which are mainly solid, liquid and gas.
There is actually one more, the fourth, which is none other than plasma.
However we won't be touching the properties of this matter in this chapter.
Eg of 3 states of matter
-Water exists is 3 states: ice(solid), water(liquid) and water vapour(gas).

The 3 states change according to it's surrounding temperature and atmospheric pressure.

The table below shoes the properties of the individual matter.

State of matter	Properties
Solid	Fixed shape and volume Normally hard and rigid, large force needed to change its shape High density Incompressible
Liquid	Fixed volume but does not have a fixed shape High density Incompressible
Gas	No fixed shape or volume Low density Compressible

Why does the properties of a substance vary depending on the state it's in?

The Kinetic Model Of Matter
-at microscopic level, all matter is made up of tiny particles called atoms or molecules(atoms joint together).
-these particles are always in continuous motion

The table below is the exlaination of the properties of matter using the kinetic model of matter

State of Matter	Movement of particles
SOLID	Vibrate about fixed position only. Held in position by very strong intermolecular bonds. Resulting in fixed volume and shapes
LIQUID	Free to move about but confined within the vessel containing it Resulting in fixed volumes but will take shape of the vessel containing it
GAS	Particles have little attraction between them. Move about freely and at very high speeds. Resulting in no fixed volume and highly compressible

Here are some videos on the molecules in solid and liquid.