Particle Model of Matter

Density

Measure of the compactness of a substance. correlation between mass and volume.

Density formula

p = m/v

Reasons for density

• Dense material will have particles tightly packed together

• Less dense material particles are more spread out

• Compress material —> particles move closer together —> density increases mass doesnt change volume decreases

Solids

• strong forces of attraction hold particles close together

• fixed regular arrangement

• minimal energy so they can only vibrate in the positions

liquids

• weaker forces of attraction between particles

• close together put can move and form irregular arrangements

• more energy than particles in solid move in random directions at low speeds

gas

• no forces of attraction between particles

• more energy in particles than lquid and solid

• free to move and travel in random directions at high speeds

Properties of solids liquids and gases

• density of a substance is highest when in solid form as particles are closest to each other

• gases and liquids can flow as their particles can move past each other solid cant

• gases are compressible as particles are very spread out solid and liquid cant get much closer together so it harder

Internal energy

Total energy that its particles have in its kinetic and potential energy stores

Changes of state examples

S <- >L = freezing + melting

L < - > G = Condensing + boiling/evaporating

S → G = subliamting

change of state

• reversible

• physical change

• no of particles do not change just arranged differently

• mass is conserved

Bond Graphs

Flat lines - > Change of state

• Up solid,liquid,gas

• Down gas,lquid,solid

Specific latent heat

Amount of energy need to change 1kg of a substance from one state to another without changing its temperature

Specific latent heat of ?

• fusion for change between liquid and gas

• vaporisation between liquid and gas

specific latent heat

E (joules energy of state) = mL

Temperature of gas 

• increases temperature of gas 

• transfer thermal energy to kinetic energy store of gas particles

Gas pressure

• when gas particles collide with a surface they exert a force on it

• pressure is force per unit area

• faster particles and more collisions with wall lead to increase is net force - gas pressure

pressure formula

pV= constant (inversely proportional)

Pressure and effect on container size

• pressure of gas is net outward force at right angles to the surface of the container

• if the outward pressure is larger than inward pressure then compresses if smaller than expands

• this happens if the containter change easily change shape

doing work on gas

• if you transfer energy by applying force you do work

• doing work on gas can increase its interal energy which can increase temp