2. Thermal physics Flashcards
Solid - Features
- Fixed shape (can alter when forces act on them)
- Usually dense + difficult to compress
Liquid - Features
- Can flow / be poured (no fixed shape)
- Takes the shape of the bottom of the container (no fixed shape)
- Fixed volume (Can’t be compressed)
Gases - Features
- Flow very quickly (faster than a liquid)
- Spread out in a container
- Easy to compress (easier than liquid)
Deposition
Changing directly from a gas to a solid.
Sublimation
Changing directly from a solid to a gas.
Condensation
The individual particles are attracted together and the bonds between them increase in strength.
- Gas –> Liquid
Evaporation
The bonds between particles are broken and the individual particles separate and move about quickly.
- Liquid –> Gas
Freezing
The bonds between the particles increase in strength and the particles end up in fixed positions.
- Liquid –> Solid
Melting
The bonds between the particles weaken and they can flow past each other.
- Solid –> Liquid
Melting point
The temperature at which a material changes from a solid to a liquid
(Same temp as the freezing point for a liquid)
Freezing point
The temperature at which a liquid will change to a solid.
(Same temp as the melting point for a solid)
Freezing point + boiling point of water
(Only applies to pure water)
Freezes at 0C
Boils at 100C
Boiling point
The temperature at which a liquid will change to a gas.
(Same temp as the condensation point for the gas)
Condensation point
The temperature at which a gas will change to a liquid.
(Same temp as the boiling point for the liquid)
Difficulties of classifying materials into states of matter.
- Not all materials fit perfectly into one of the three states eg. Jelly.
- Materials can also contain a combination of states of matter. Eg- A sponge is solid but contains air pockets so it can be compressed.
Molecular structure of a solid
- Closely packed particles in a regular pattern
- Held in place by strong, attractive forces
- Particles vibrate around their positions
- If you try to compress a solid –> the forces holding the particles in position becomre more repulsive –> keeping the particles the same distance apart
Molecular structure of a liquid
- Molecules are still very close together.
- Arranged irregularly –> can therefore move past each other
- Weaker forces of attraction in liquids than in solids.
Molecular structure of a gas
- Particles are spread out
- Move around fast
- Irregular arrangement
- Weak forces of attraction between them (don’t attract each other –> so spread out)
- Particles far apart so can be compressed
A gas cools down
- Particles slow down
- Eventually move slow enough that forces can form between them
- Join together + material becomes a liquid.
A liquid cools down
- Particles slow down
- Particles lose enough energy to form a fixed structure
- Material becomes solid
A solid cools down
- Particles vibrate but as temp decreases, the vibrations become smaller and smaller
- Eventually the particles has the least possible kinetic energy (absolute zero)
Absolute zero
0 Kelvin (0K)
-273 C
20 C = 293 K
Gas pressure
The outward force on the walls of a container caused by the gas particles colliding with the walls.
What happens to the pressure of a gas as temperature changes?
As temperature increases –> particles move faster
–> More collisions with the surface of the container surrounding the gas –> This creates pressure.