THE KINETIC MODEL OF MATTER
STATES OF MATTER
solid: occupies a fixed volume and has a fixed shape
liquid: occupies a fixed volume and takes the shape of its container
gas: expands to fill its container and takes its shape
Changes of state
melting: from solid to liquid
boiling or evaporation: from liquid to gas
condensing: from gas to liquid
freezing: from liquid to solid
How does a change of state happen?
If we supply energy to ice, its temperature will rise until it arives at 0°C (melting point). At this temperature the ice begins to melt and even if we continue to supply energy, the temperature does not rise.
When the ice is completely melted, the temperature rises again up to 100 ° C (boiling point). The water begins to turn into vapor and the temperature stops rising again for an even longer period, until all the liquid has become vapor.
When a substance is heated, its particles start to vibrate more and more strongly until some of the bonds are broken
The particles of solids and liquids stick together because there are attractive forces (or bonds) between them
FORCES AND THE KINETIC THEORY
THE KINETIC MODEL OF MATTER
kinetic model of matter = related to the movement of particles
Arrangements of particles
solid: the particles are packed closely together and are in close contact with their neighbours; they cannot move around, they can only vibrate about a fixed position
liquid: the particles are slightly less tightly packed than in a solid and they can move around
gas: the particles are wide separated from one another, they are no longer in contact and they can move freely about
Brownian motion
Robert Brown observed the behavior of some grains of dust in the water and noticed them jiggling about.
It happens because the moving particles are constantly buffeted by the fast-moving particles of the air.
We can witness the same phenomenon if we look with a microscope at the smoke particles enclosed in a smoke cell.
Evaporation
evaporation = transition from liquid to vapour at a temperature below the boiling point
vapour = a gas at a temperature below its boiling point
The particles of a liquid move and some move faster than others. Some can move fast enough to escape the surface of the water and become vapor particles in the air.
Evaporation makes things cooler because because the particles that escape from the water are the fastest-moving and the ones with the most energy.
GASES AND THE KINETIC THEORY
Gay-Lussac's law
Boyle's law
For a gas, temperature and pressure are directly proportional. As the temperature of a gas goes up, its pressure goes down. As the temperature of a gas goes down, its pressure goes down.
Gay-Lussac estabilished a gas law describing the relationship between temperature and pressure.
Gay-Lussac's law: when the volume and the amount of gas are constant, pressure and temperature are directly proportional
P₁/T₁ = P₂/T₂
For a gas, pressure and volume are inversely proportional. As the pressure on a gas goes up, its volume goes down. As the volumes a gas occupies goes up, its pressure goes down.
Robert Boyle stated the inverse relationship between pressure and volume as a gas law.
Boyle's law: for a given amount of gas, at fixed temperature, pressure and volume are inversely proportional.
P₁V₁ = P₂V₂