1. ENERGY CHANGES & STATES OF MATTER

2. GAS LIQUID SOLID CHANGE OF STATE Evaporation Condensation Melting
Boiling point
LIQUID
Melting
Freezing
Melting* point
SOLID

3. When a liquid EVAPORATES, the energy to BREAK THE BONDS between the liquid particles is taken from the liquid...
ENERGY OUT
...which cools down
Higher – continue to speed distribution
Foundation jump to examples

4. In a liquid (or a gas) where the particles are moving around, they move at DIFFERENT SPEEDS.
FAST
SLOW

5. When a liquid evaporates, only some of the particles have enough energy to escape the liquid (evaporate).
Because the high energy particles escape, the AVERAGE energy of those left behind GOES DOWN – so the liquid cools
Number of particles
Energy
Energy needed to escape the liquid
These move too slowly so stay behind in liquid
These move fast enough to escape

6. What happens when the temperature of the liquid increases?
Number of particles
40°C
70°C
100°C
Particles need to move faster than 750 m/s to escape the liquid
What happens to the rate of evaporation as the temperature increases? Why?
What else do you notice about the graph for 100°C ?

7. Liquids which evaporate quickly feel COLD on the skin
Evaporation ABSORBS ENERGY from the surroundings which COOL DOWN
Unglazed clay pot soaked in water cools as water evaporates
Liquids which evaporate quickly feel COLD on the skin

8. When a gas CONDENSES, energy released by making new bonds between the liquid particles goes into the liquid.....
ENERGY PUT IN
...which heats up.

9. Condensation RELEASES ENERGY to the surroundings which HEAT UP
The heat released by the condensation of water vapour over the ocean provides most of the kinetic energy of a hurricane
Water vapour condensing on a cold window warms it up.

10. When a gas EXPANDS, the energy needed for the particles to move further apart is taken from the surroundings...
ENERGY REMOVED
ENERGY REMOVED
...which cool down.

11. When a gas expands quickly it cools down
Gas expanding out of a CO2 cylinder leaves it covered in frost
Aerosol sprays get very cold as the gas inside expands (the mist that can be seen is droplets of liquid mixed with the gas)

12. When a gas is COMPRESSED, the energy used to force the particles closer together ends up giving them extra kinetic energy..
ENERGY PUT IN
...so the gas heats up.

13. When a gas is compressed quickly it 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

14. Air (blue) is drawn in (1) The air is COMPRESSED and HEATS UP (2)
In a DIESEL ENGINE air is compressed so much it gets hot enough to ignite the fuel
FUEL
EXHAUST
AIR
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)

15. SUMMARY COMPRESSING a gas HEATS IT UP CONDENSATION causes HEATING
EXPANDING a gas COOLS IT DOWN
EVAPORATION causes COOLING