Unit R - Solids, liquids, gases (copy)

5c (5.9-5.10), 5d (5.15-5.22)

Solid

Solid

• Strong forces of attraction hold particles close together in fixed, regular arrangement

• Particles don’t have much energy so can only vibrate about fixed positions

Liquid

• Weaker forces of attraction between particles

• Particles close together, but can move past each other and form irregular arrangements

• More energy than particles in solid

• Particles move in random directions at low speeds

Gas

• Almost no forces of attraction between particles

• Particles have more energy than those in liquids/solids

• Free to move

• Travel in random directions at high speeds

Melting

Extra energy makes particles vibrate faster until eventually forces between them are partly overcome and particles start to move around

Boiling

When you heat liquid, extra energy is transferred into particles’ KE stores, making them move faster

Eventually, when enough of particles have enough energy to overcome attraction to each other, big bubbles of gas form in liquid

Evaporation

• When particles escape from liquid and become gas particles

• Particles can evaporate from liquid below liquid’s boiling point

• Particles near surface of liquid can escape and become gas particles if:

  • Particles are travelling in right direction to escape liquid

  • Particles are travelling fast enough (have enough energy in KE stores) to overcome attractive forces of other particles

• Fastest particles are most likely to evaporate from liquid
  When they do, the avg. speed + energy in KE stores of remaining particles decreases

• Decrease in avg. particle energy means temp of remaining liquid falls - liquid cools

Gas pressure

• As gas particles move around, they randomly collide with each other and whatever else is in the way

• Gas particles have mass, though very light
  When they collide with something, they exert force on it and their momentum + direction change
  In sealed container, gas particles smash against wall’s - creating outward pressure

• Pressure depends on speed of particles + how often they hit walls

Absolute zero

273ᵒC / 0K

The coldest that anything can ever get

At absolute zero, particles have as little energy in KE stores as possible

Start of Kelvin scale

Temp conversion (ᵒC to K)

ᵒC → K = +273

K → ᵒC = -273

Gas temp and speed of particles

• Gases consist of very small particles, constantly moving in random directions
  Particles take up hardly any space

• Particles constantly collide with and bounce off each other + container walls

• If you increase temp of gas, particles get more energy
  Double temp (measured in K) = double average energy in KE stores of particles

• As you heat up gas, average speed of particles increases
  Anything moving has energy in KE store, equal to 1/2mv²

Relationship of pressure and volume in gas

• Same fixed amount of gas in bigger container = pressure decrease, due to fewer collisions between gas particles and container walls

• When volume reduced, particles get more squashed up and hit walls more frequently → larger force over smaller SA → increased pressure

Relationship of pressure and temp in gas

• If you heat gas, particles move faster + have more energy in KE stores

• Increase in energy → particles hit container walls harder and more frequently → larger force → more pressure

• Temp (in K) and pressure are proportional - double temp of fixed amount of gas = double pressure

Equation: Pressure and Temp for fixed mass of gas at constant volume

Pressure₁/Temp₁ = Pressure₂/Temp₂

p₁/T₁ = p₂/T₂

[Pa]/[K] = [Pa]/[K]

Equation: Pressure and Volume for fixed mass of gas at constant temp

Pressure₁*Volume₁ = Pressure₂*Volume₂

p₁V₁ = p₂V₂

[Pa]*[m³] = [Pa]*[m³]