Three states of matter that most substances exist in at room temperature
Solids
Have a fixed volume and fixed shape
Cannot flow because particles cannot move from place to place
Cannot be compressed because particles are close together and have no space to move into
Liquids
Have a fixed volume but no fixed shape
Can flow and take the shape of their container because particles can move around each other
Cannot be easily compressed because particles are close together and have no space to move into
Gases
Have no fixed shape or volume
Can flow and completely fill their container because particles can move quickly in all directions
Can be compressed because particles are far apart and have space to move into
Particle model
Explains the difference between solids, liquids and gases
All substances are made up of particles
The particles are attracted to each other
Some particles are attracted strongly to each other and others weakly
The particlesmove around and have kinetic energy
The kineticenergy of the particles increases with temperature
Properties of solids, liquids and gases
Solids: Fixed volume and shape, cannot flow, cannot be compressed
Liquids: Fixed volume, no fixed shape, can flow, cannot be easily compressed
Gases: No fixed shape or volume, can flow, can be compressed
Changes of state
Reversible changes due to changes in pressure or temperature, unlike chemical reactions no new substance is formed
Melting
1. Solid changes into liquid
2. Occurs at melting point
3. Heat is absorbed during melting
4. Impurities lower melting point and increase boiling point
Pure substances melt and freeze at the same temperature, impure substances melt and boil through a range of temperatures
During melting, heat energy is absorbed by the particles and converted to kinetic energy, causing the particles to vibrate faster and overcome attractive forces
Temperature remains constant during melting as the absorbed heat energy is used to weaken attractive forces between particles, not increase kinetic energy
Boiling
1. Liquid changes into gas
2. Occurs at boiling point
3. Heat is absorbed during boiling
4. Higher pressure results in higher boiling point
5. Impurities affect boiling point
During boiling, heat energy is absorbed by the particles, increasing their kinetic energy until they have enough energy to overcome attractive forces and escape the liquid to form a gas
Temperature remains constant during boiling as the absorbed heat energy is used to weaken attractive forces between particles, not increase kinetic energy
Evaporation
Liquid changes into gas, occurs at surface of liquid, no fixed temperature, takes place below boiling point
Condensation
Gas changes to liquid when cooled to boiling point, heat is released to surroundings
Freezing
Liquid changes into solid, occurs at freezing point, impuritieslower freezing point
Sublimation
Solid changes directly into gas, heat is absorbed, examples include dry ice, iodine, ammonium chloride
The state of a substance at a given temperature can be predicted if its melting and boiling points are known
Oxygen
Melting point -218°C, boiling point -183°C, so at -200°C oxygen will be in the liquid state
Heating curve
Graphical representation of changes of state during heating, shows melting and boiling
Cooling curve
Graphical representation of changes of state during cooling, shows condensation and freezing