LAST CHAPTER!
CHAPTER 9 - THERMAL PROPERTIES OF MATTER!
SO!
WHAT IS INTERNAL ENGERGY?
- Internal energy is actually, the energy found in the particles that causes them to vibrate :D
- internal energy comprises both K.E. and P.E. (in case you don't know what it is, -.- it's kinetic energy and potential energy!)
Kinetic energy of internal energy is due to the vibration of the particles.
- the higher the temperature, and more vigorous the movements
- in fluids (liquids and gases) K.E. is due to movement
Potential energy of the internal energy is due to the stretching and compressing of the intermolecular bonds (a force that holds particles in solids together) as the particles vibrate
- P.E. stored depends on the force between particles and how far they are from each other :D
Melting and Solidification
Melting:
-When a solid, when heated,changes to a liquid, the change of state (from solid to liquid) is called melting!
- melting occurs at a constant temperature in pure substances (it's called the melting point)
How do solids melt? hmm..
In order for a solid to melt, intermolecular bonds within the solid must be broken.
Since ENERGY is need to break the bonds,
thermal ENERGY is supplied for a period of time for the intermolecular bond to break
Once the intermolecular bonds have broken, the particles can move freely (in liquid state).
Solidification
It's the reverse of melting!
- when liquids becomes a solid again.
- a PURE substance will freez at the temperature equal to it's melting point
- we call that temperature the freezing pont as well.
OOOOOOOOOOHHHHHHH frozen water is COOL...
literally.
BOILING
When a PURE substance changes from liquid to a vapour at a fixed temperature, the process is called boiling and the temperature of which it changes state is called the boiing point.
CONDENSATION
It the reverse of BOILING. It changes state (from gas to liquid) at the same temperature as it's boiling point. Thermal energy is given off.
How does a liquid boil?
Thermal energy causes the molecule to be further apart with negligile intermolecular frces between the particles. When this happens, a change of state (liqud to gas) occurs.
EVAPORATION
Evaporation is like boiling. It is when liquid changes state and becomes gas.
THE DIFFERENCE BETWEEN EVAPORATION AND BOILING!
- NUMBER ONE!: Boiling occurs at a FIXED temperature but evaporation occurs at ANY temperature.
- NUMBER TWO!: boiling is a quick process, evaporation is SLOW....
- NUMBER THREE!: boiling takes place THROUGHOUT the liquid, evaporation takes place only on the surface of the liquid
- NUMBER FOUR!: bubbles ar formed in the water duing boiling, and none are formed in evaporation
- NUMBER FIVE!: temperature remains constant in boiling and temperature might change in evaporation
- NUMBER SIX!: in boiling, thermal energy is supplied by the energy source, whereas in evaporation, therma enery is supplied by the surrounding temperatures
more bout evaporation:
EVAPORATION CAUSES COOLING!
When water evaporates from your skin, thermal energy is taken away as well.
And therefore your body cools....
How does evaporation occur?
It occurs when energetic molecules overcome the downward attractive forces of other molecules and escape. Carrying with it thermal energy.
APPLICATION of EVAPORATION
- when perspiration evaporates off your skin
- wet clothes or puddles of water dry off after some time
- when a person has a fever, the person is sponged with water. when water evaporates from the person's skin, heat will be slighly removed.
- refrigerators use the concept of condensation and evaporation to keep its things cool
Factors that effect evaporation
1. TEMPERATURE (the higher the temp, the higher the rate of evaporation)
2. HUMIDITY OF THE SURROUNDIND AIR (the higher the humidity, the lower the rate of evaporation)
3. SURFACE ARE OF THE LIQUID (the bigger the surface area, the higher the rate of evaporation)
4. MOVEMENT OF AIR (the higher the movement in air, the higher the rate of evaporation)
5. PRESSURE (the lower the pressure, the higher the rate of evaporation)
6. BOILING POINT OF THE LIQUID (the higher the temp, the lower the rate of evaporation)
video time!
hahahha enjoy!
that's all for chapter 9!
*cheers*
here's something to laugh at.
hahahahah lecturers are awesome!
HOLLA!
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