changing state

what do the strength of the forces of attraction between materials depend on?

• material (structure, type of bonds)

• temperature

• pressure

describe (particles in) gases:

• very weak forces of attraction between particles

• don’t keep a definite shape/volume

• free to move

• far apart

• travel in straight lines

what happens to gases when they are heated?

• expand

• pressure increases

• particles move faster

describe (particles in) liquids:

• weak forces of attraction between particles

• randomly arranged

• free to move past each other, but tend to stick closely together

• definite volume, but not a definite shape

• particles constantly moving with random motion

what happens to liquids when they are heated?

• expand slightly

• particles move faster

describe (particles in) solids:

• strong forces of attraction between particles

• fixed positions

• regular lattice arrangement

• keep a definite shape/volume (particles don’t move)

• vibrate about their positions

what happens to solids when heated?

• vibrate faster

• expand slightly

how do solids change to liquids?

1. particles gain energy when heated

2. vibrate more = weakens forces holding the solid together

3. at a certain temperature (melting point), particles have enough energy to break free from their positions - melting

how do liquids change to gases?

1. liquid heated = particles gain more energy

2. particles move faster = weakens and breaks bonds of the liquid

3. at a certain temperature (boiling point), particles have enough energy to break bonds - boiling/evaporating

how do gases change to liquids?

1. gas cools = particles don’t have enough energy to overcome the forces of attraction between

2. at the boiling point, many bonds are formed - condensing

how do liquids change to solids?

1. liquid cools = particles have less energy

2. not enough energy to overcome attraction between particles so more bonds form

3. melting point = so many bonds formed that they’re held in place - freezing

what does the amount of energy needed for a substance to change state depend on?

• how strong the forces between particles are

• stronger forces = more energy needed = higher melting/boiling point of substance