Thermal Properties of Matter

INTERNAL ENERGY

Definition:

Internal energy is the total energy of particles that are in a solid, vibrating about their fixed positions and held together by interatomic bonds.

2 components:

1. Kinetic component

-due to the vibration of the particles

-DIRECTLY related to temperature

-the higher the temperature, the more vigorous the vibrations of the particles

2. Potential component
-due to the stretching and compressing of the interatomic bonds as particles vibrate

-amount of potential energy stored in the bonds depends on: force between particles

: distance between particles

MELTING & SOLIDIFICATION
Melting

Solids melt at a certain temperature. The melting point of ice, for example, is zero degrees celsius. During the change of state from ice to water, there is no change in temperature even though thermal energy is being absorbed.

How does a solid melt?

-The molecules in a solid are held by strong interatomic bonds

-When these bonds are broken by thermal energy, the molecules can move out of their fixed positions and hence change state.

Solidification

It is the reverse process of melting. It changes a liquid into a solid.

BOILING & CONDENSATION

Boiling

When a liquid is heated and changes state to a gas at a certain temperature, boiling takes place.

-A liquid boils when thermal energy separates the molecules and pushes back on the atmosphere.

-The molecules are further apart and the forces of attraction is much weaker.

-Boiling occurs at a fixed temperature

-Boiling is a quick process which takes place throughout the liquid

-The temperature remains constant throughout

-Thermal energy is supplied by an energy source

Condensation

Condensation is the exact oppposite of boiling.

-It is the change of state from vapour to liquid when a substance is cooled at the same constant temperature.

EVAPORATION

Evaporation is the change of state from liquid to gas. However, it differs from boiling in a few ways.

-Evaporation occurs at ANY temperature

-It is a slow process

-Takes place only at the liquid surface

-Temperature may change

-Thermal energy is supplied by the surroundings

Evaporation also causes cooling.

Evaporation occurs when the molecules of the liquid move at different speeds randomly. At the liquid surface, the more energetic molecules are able to overcome the downward attractive forces of either molecules and escape into the atmosphere. This leaves a liquid with not so energetic molecules.

Factors to take into consideration:

1. Temperature

2. Humidity of surrounding air

3. Surface area of liquid

4. Movement of air

5. Pressure

6. Boiling point of liquid

END OF CHAPTER 9!!!

Transfer of Thermal Energy

Transfer of thermal energy.

1. Thermal energy is transferred ONLY when there is a difference in temperature.

-Transferred by conduction, convection and radiation

2. Thermal energy ALWAYS flows from a region of higher temperature to a region of lower temperature.

3. Thermal equilibrium is no gain or loss of thermal energy

CONDUCTION

Definition:

Conduction is the process of thermal energy transfer without any flow of the material medium.

Doing an experiment involving different metal rods coated with wax, a few observations and conclusions can be drawn.

1. Thermal energy flows through the material of each rod without any flow of the material itself.(similar to sound energy for e.g, the object is not transferred though the energy is) Such is called conduction.

2. Different materials conduct heat at different rates.

Conduction in liquids and gases

-process of conduction is inefficient

-particles in liquids and gases are spaced further apart than those in solids

-hence transfer of kinetic energy is slower

-hence air is a poor conductor of heat compared to water

-solids are still the best conductors

Fun fact:

Have you ever noticed that metals tend to feel cold? Believe it or not, they are not colder! They only feel colder because they conduct heat away from your hand. You perceive the heat that is leaving your hand as cold.

CONVECTION

Definition:

Convection is the transfer of thermal energy by means of currents in a fluid (liquids or gases)

How convection works:

When water is heated, it expands and becomes less dense than the surrounding water. It therefore starts to rise while the cooler regions in the upper part sink. This movement is due to a difference in its density and sets up a convection current.

Convection currents occur only in fluids but not in solids as convection involves the bulk movement of the fluids which carry thermal energy with them.

RADIATION

Definition:

Radiation is the continual emission of infrafred waves from the surface of all bodies, transmitted without the aid of a medium.

Absorption of infrared radiation

-Infrared radiation is absorbed by all objects and surfaces

Factors that affect rate of infrared radiation

1. Colour and texture of the surface

-Black surfaces are better absorbers of infrared radiation than shiny white surfaces.

2. Surface temperature

-The higher the temperature of the surface of the object relative to the surrounding temperature, the higher the rate of infrared radiation.

3. Surface area

-The object with the larger surface area will emit infrared radiation at a higher rate.

Applications of thermal energy transfer:

CONDUCTION

1. Cooking utensils

2. Soldering iron rods

(these are the good conductors of heat)

3. Handles of utensils

4. Table mats

5. Woollen clothes

(these are the bad conductors of heat)

CONVECTION

1. Electric kettles

2. Air conditioners

3. Refrigerators

RADIATION

1. Teapots

2. The Greenhouse

END OF CHAPTER 8!!!

Matter

CHAPTER 7

I just finished reading chapter 7 and I discovered that Chem and Physics is kind of connected, especially in the arrangement of particles in the 3 defferent states. We just learnt the exact same thing a few months ago. The first part of this chapter is really a revisit of lower secondary work, about the properties of solid, liquids and gases.This is a solid wall and if you see the way the molecules are arranged in this wall, its kind of interesting.

Okay just look at the liquid inside the glass.

The last one now, gas and their molecules (look at the smoke)

The pictures of the molecules above are called the kinetic model of matter. To break it up a bit,

Solid:

-Molecules are packed together in an orderly and fixed fashion

-high density

-vibrate only about their fixed positions

-hence they have fixed volumes and shapes

Liquid:

-Molecules are packed together (not as much as solid) in a random arrangement

-relatively high densities

-free to move about the liquid

-hence they have fixed volumes but NOT fixed shapes

Gas:

-Molecules are very far apart and randomly arranged

-very low densities

-molecules move about randomly at high speeds

-easily compressed

Brownian motion

It is the random or irregular motion of smoke particles in air that only occurs in fluids (gas or liquids).

You can go to this website it has a short clip on how the particles move.

http://www.aip.org/history/einstein/brownian.htm

How does temperature affect it?

Air molecules have greater speeds at higher temperatures. When the temperature increases, a larger amount of thermal energy is converted to kinetic energy of the air molecules, causing them to move faster.

END OF CHAPTER 7!!!