Friday, September 5, 2008
EVAPORATION-change of state from liquid to gas.
-can occur at any temperature.
-slow process
-takes place only at the liquid surface
-no bubbles are formed in the liquid.
-temperature may change
-thermal energy supplied by the surroundings.
evaporation causes cooling.
Applications of evaporation
-experience cooling effect
-wet clothes/puddles will evaporate after awhile.
-refridgerator:
it uses the principles of condensation and evaporation to keep its content cold
Factors
- temperature
raising the temperature= increase^ rate of evaporation
- humidity of the surrounding air
humid increase = rate of evaporation decrease
- surface area of the liquid
larger surface area= rate of evaporation increase^
- movement of air
surrounding air is moving= rate of evaporation increase^
- pressure
reduced atmospheric pressure= rate of evaporation increase^
- boiling point of liquid
liquid with lower boiling points evaporate faster.
and finally we come to the end of this very long chapter.
hope that you guys would find my blog useful.
~~~~~~~The End~~~~~~~
Posted @ 4:49 AM
Posted @ 4:32 AM Melting
-occurs when solid changes into liquid upon heating.
-when a pure substance melt at a particular point= melting point
*For a solid to melt, the strong intermolecular bonds that holds the molecules in the solid together have to be broken
*once the intermolecular bonds are broken, the molecules can move out of their fixed position, therefore, the solid melts
solidification
-reverse process of melting
-changing liquid into solid without change of temperature.
-when liquid molecules come together and solidify, intermolecular bonds are formed, and thermal energy is released.
click on the link to see a demostration on changing water into ice.
http://www.youtube.com/watch?v=R5FjY4qjl9k&feature=related
Posted @ 3:38 AM
(Potential Energy is stored in the slinky(above^) as it stretched or compressed.
much like the intermolecular or interatomic bonds of particles.)
Posted @ 3:02 AM
Wednesday, September 3, 2008
chapter 8-transfer of thermal energy- thermal energy is transferred only when there is a diffrence in the temperature.
- thermal energy always flows from a region of higher temperature to a region of lower temperature.
how is thermal energy transferred
1. conduction
2.convection
3.radiation
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Conduction
e.g
if 1 end of a metal rod is heated with a flame,the other end of the rod would also become hot after a while.
reasoning: thermal energy is transferred from one end of the rod to the other.
CONDUCTION is the the process of thermal energy transfer without any flow of the material medium.
good conductors of heat : metals like copper, silver and iron
bad conductors of heat : non-metal like glass, plastic, wood, brick, wool, water and air
-the transferring of thermal energy from the hot end to the cold end by atomic/molecular vibration can take place in both metals and non-metals.
-when Thermal energy is supplied to one end of the medium, the particles at the hot end will vibrate vigorously
-the higher the temperature, the more vigorous the particles.
-this causes the neighbouring particles to vibrate as well
conduction is liquid and gases
-thermal energy is conducted from a hotter region to a cooler region.
-particles in liquid & gases is spaced further apart than those in solid, therefore , collisions are less frequent
-the transfer of kinectic energy from the fast-moving particles to neighbouring particles is slower.
CONVECTION
-it is the transfer of thermal energy by means of currents in a fluid(liquid/gas)
http://www.youtube.com/watch?v=G31NpGlWuUk&feature=related
the link above shows a demostration of convection in water.
reasoning:
-when water at the bottom is heated, it expands.
-the expanded water is less dense than the surrounding water, therefore, it rises.
-and the cooler regions of the water, being denser, would sink.
-the movement of water is due to the diffrence in density sets up a convection current.
TAKE NOTE: convection currents occurs only in fluids such as liquids and gases BUT not in solid
RADIATION
-its the continual imission of infared waves from the surface of all bodies, transmitted without the aid of a medium.
-it DOES NOT need a medium for energy transfer.
-therefore, it CAN take place in vacumn-
-thermal energy from infrared waves is called radiant heat.
Absorption of infrared radiation
-infrared absorption is absorbed by ALL objects and surfaces.
-the absorbtion of radiant heat causes a temperature rise
EMISSION of infrared radiation
-infrared radiation is emitted by ALL objects and surfaces.
-this would cause the temperature of the objects to fall.
factors that affects the rate of infrared radiation
-Colour and texture of surface
- dull,black surfaces are better absorbers than shiny white surfaces.
- also, dull,black surfaces are better emitters of infrared radiation
-Surface temperature
The higher^ the temperature of the surface of the object relative to the surrounding temperature, the higher^ the rate of infrared radiation.
-surface area
- the larger the surface area, the more infrared radiation will be emitted at a higher rate.
~~~~~~~END OF(a long long long) CHAPTER~~~~~~~
Posted @ 3:33 AM chapter 7: kinetic models of matter
7.1- states of matter
SOLID
-fixed shaped
-fixed volume
-high density
-incompressible
-hard and rigid
-needs a large amt of force to change shape
LIQUID
-fixed volume
-NOT fixed shape
-high density
-incompressible
GAS
-NO fixed shape or volume
-low density
-compressible
arrangement of particles.
SOLID
why does solid have high densities?
1.closely packed together.
2.regular patterns.
3. occupy minimum space.
why does solid have fixed volume and shape?
1.particles vibrate about fixed position only.
2.it is held in position by strong INTERMOLECULAR bonds.
LIQUID
why does liquid have high densities?
1.particles randomly arranged
2.particles slightly furher apart.
(compared to solid)
why does liquid have fixed volume BUT will take shape of the object containing them?
1.free to move about.
2.BUT confined within the vessel
3.have attractive forces between particles.
GAS
why does gas have low densities?
1.particles are far apart
2.randomly arranged
3.occupy any available space
why does gas have no fixed volume & shape?
why does gas are highly compressible?
1.particles have very little attraction.
2.move about randomly at very high speed.
------------------------------------------------------------------
BROWNIAN MOTION
defined as:
random movement of mircoscopic particles suspended in fluid
click link to see demostration of the BROWNIAN MOTION
http://www.aip.org/history/einstein/brownian.htm
the brownian motion of smoke will be more vigorous and agitated at a higher temperature because the air molecules have greater speed at higher temperature.
Temperature increase^= LARGER amt of thermal energy is CONVERTED to kinetic energy.
this will cause the molecules to move faster.
~~~~~~~END OF CHAPTER (^^)v~~~~~~~
Posted @ 12:41 AM