ENERGY CHANGES & STATES OF MATTER. Evaporation Melting Condensation F reezing Melting* point Boiling point SOLID LIQUID GAS CHANGE OF STATE.

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