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.
How a hot air balloon is inflated (pressure + temperature
- Air is heated inside the balloon
–> Temperature increases so gas particles move faster + collide more with balloon material
–> Creates gas pressure
–> As prcessure increases, balloon inflates.
Increasing temperature of a gas
- Particles move faster
- Not all particles move at the same speed because collisions cause diffrent speeds etc.
- Therefore there is a range of speeds
- Temperature of gas is related to the mean/average speed.
The hotter the gas –> the higher the mean speed of particles
Momentum + pressure in gases (changing temperature)
- If temp increases –> velocity increases –> momentum increases –> force increases –> higher pressure
How to increase pressure of a gas
Double the rate of particles in balloon = double the collision = double the force on the rubber = double the force per unit area or double the pressure.
Brownian motion
- The random motion of small, microscopic particles caused by collisions with even smaller, invisible particles.
Named after Robert Brown’s observations of the movement of pollen grains in water.
Describing brownian motion
- Cause by the impacts of molecules or atoms on larger particles (eg. pollen grains)
- Pollen grains are too small to see individually (microscopic)
- Molecules / atoms cannot be seen even with a powerful microscope –> NOT microscopic therefore.
Why brownian motion works
Small + fast-moving object = momentum of large + slow-moving object.
Therefore small molecules can still collide and have an impact on particles thousands of times larger.
Relationship between pressure of a gas and temperature - Graph
As temperature increases, pressure increases (positive correlation)
Linear graph.
Affect of volume of a gas on pressure
- Volume of a container decreases –> distance gas particles travel between collissions with walls decreases
–> more collision –> increased pressure
(Gas becomes more compressed)