energy changes & states of matter. evaporation melting condensation f reezing melting* point...
TRANSCRIPT
ENERGY CHANGES & STATES OF MATTER
Evaporation
Melting
Condensation
Freezing Melting* point
Boiling point
SOLID
LIQUID
GAS
CHANGE OF STATE
ENERGY OUT
When a liquid EVAPORATES, the energy to BREAK THE BONDS between the liquid particles is taken from the liquid...
...which cools downHigher – continue to speed distribution
Foundation jump to examples
In a liquid (or a gas) where the particles are moving around, they move at DIFFERENT SPEEDS.
SLOW FAST
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Energy
Energy needed to escape the liquid
When a liquid evaporates, only some of the particles have enough energy to escape the liquid (evaporate).
These move fast enough to escape
These move too slowly so stay
behind in liquid
Because the high energy particles escape, the AVERAGE energy of those left behind GOES DOWN – so the liquid cools
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40°C
0°C
70°C
100°C
Particles need to move faster than 750 m/s to escape the liquid
What happens when the temperature of the liquid increases?
What happens to the rate of evaporation as the temperature increases? Why?
What else do you notice about the graph for 100°C ?
Evaporation ABSORBS ENERGY from the surroundings which COOL DOWN
Liquids which evaporate quickly feel COLD on the skin
Unglazed clay pot soaked in water cools as water evaporates
ENERGY PUT IN
When a gas CONDENSES, energy released by making new bonds between the liquid particles goes into the liquid.....
...which heats up.
Condensation RELEASES ENERGY to the surroundings which HEAT UP
Water vapour condensing on a cold window warms it up.
The heat released by the condensation of water vapour over the ocean provides most of the kinetic energy of a hurricane
ENERGY REMOVED
ENERGY
REMOVED
...which cool down.
When a gas EXPANDS, the energy needed for the particles to move further apart is taken from the surroundings...
Gas expanding out of a CO2 cylinder leaves it covered in frost
When a gas expands quickly it cools down
Aerosol sprays get very cold as the gas inside expands (the mist that can be seen is droplets of liquid mixed with the gas)
ENERGY PUT IN
When a gas is COMPRESSED, the energy used to force the particles closer together ends up giving them extra kinetic energy..
...so the gas heats up.
The valve on a bicycle pump can get very hot when air is pumped hard through it In a fire piston the air is compressed
so quickly it gets hot enough to ignite cotton wool put inside
When a gas is compressed quickly it heats up.
In a DIESEL ENGINE air is compressed so much it gets hot enough to ignite the fuel
Air (blue) is drawn in (1)
The air is COMPRESSED and HEATS UP (2)
Fuel is injected and explodes (3)
Exhaust gases (brown) are pushed out (4)
FUEL
AIREXHAUST
SUMMARY
COMPRESSING a gas HEATS IT UP
EXPANDING a gas COOLS IT DOWN
CONDENSATION causes HEATING
EVAPORATION causes COOLING