What are the key learning points about kinetic theory?
Kinetic theory describes Sub-atomic particles and anything made from them, such as atoms and molecules, are matter. Energy and forces are not matter. as a large number of A particle is a tiny piece of matter which is too small to be seen. Particles can be atoms, molecules or ions..
In solids, the particles are in fixed positions, can only vibrate and have strong forces between them.
In liquids, the particles are mainly touching, but some gaps have appeared in the structure; these gaps allow the particles to move.
In a gas, the particles have larger gaps between them and are entirely free to move; the forces between particles are weak.
What are the different states of matter?
All Sub-atomic particles and anything made from them, such as atoms and molecules, are matter. Energy and forces are not matter. consists of particles including All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. and A collection of two or more atoms held together by chemical bonds..
In everyday life, there are three states of matter - solids, liquids and gases.
The differences between the three states are due to the arrangement and spacing of the particles and their motion.
All matter contains particles.
The difference between the different states of matter is how these are arranged.
Solids
The particles in a solid:
- sit very closely together
- are in a regular arrangement and in fixed position
- vibrate about a fixed position but do not move through the solid
- are held together by strong forces
This explains why solids have a fixed shape and The volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 cm3..
Liquids
The particles in a liquid:
- sit close together but some gaps have appeared
- can move past each other because of the gaps
- have enough energy to prevent the forces between them holding them in a fixed, regular arrangementare randomly arranged
- this explains why liquids have a fixed volume but take on the shape of their container ie no fixed shape
Gases
The particles in a gas:
- are much further apart
- are entirely free to move because the forces between them are weak
- are randomly arranged
- move quickly and randomly in all directions
- this explains why gases completely fill their container and have the same volume as their container ie no fixed shape and no fixed volume
Key facts
In solids the particles are in fixed positions; the only motion allowed to them is vibration; the particles are held by strong forces; this explains why solids have a fixed shape and volume.
In liquids the particles are mainly touching, but some gaps have appeared in the structure; these gaps allow the particles to move and, although there are also forces between them, the particles have enough energy to prevent the forces holding them in a fixed arrangement; this behaviour of particles explains why liquids have a fixed volume but take on the shape of the container.
In a gas the particles have larger gaps between them and are entirely free to move; the forces between particles are weak and this explains why gases completely fill their container.
What is density?
Density of solids, liquids and gases
The difference between the densities of solids, liquids and gases is due to the distance between the particles in each state of Sub-atomic particles and anything made from them, such as atoms and molecules, are matter. Energy and forces are not matter..
Solids and liquids
The particles of a solid are very close together.
It melts when it changes from the solid state to the liquid state.
The particles remain close together, so there is usually only a small increase of The volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 cm3..
The same mass of liquid will have slightly greater volume than the solid.
As density equals \(\frac{\text{mass}}{\text{volume}}\), the liquid will have slightly lower density.
The density of solid iron = 7.8 g/cm3
The density of liquid iron = 6.9 g/cm3
Liquids and gases
A substance evaporates when it changes from the liquid state to the gas state.
Its particles move freely and are very far apart, so there is a large increase of volume.
The same The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). of gas will have very much greater volume than the liquid, and so will have much lower density.
The density of liquid oxygen = 1.1 g/cm3
The density of gaseous oxygen = 0.0014 g/cm3
| State | Distance between particles | Density | Density in g/cm3 |
|---|---|---|---|
| Solid | Very close together | High | Solid iron = 7.8 |
| Liquid | Slightly further apart than a solid | Slightly less than the solid | Liquid iron = 6.9 |
| Gas | Very much further apart than a solid or liquid | Very much less than the solid or liquid | Oxygen gas = 0.0014 |
How to calculate density
The density of a material is the mass of 1 cm3 (or 1 m3) of the material. It is a measure of the compactness of a material. Density is measured in grams per centimetre cubed (g/cm3) or kilograms per metre cubed (kg/m3). can be calculated using the equation:
Density = \(\frac{mass}{volume}\)
D = \(\frac{m}{V}\)
D = density in g/cm3
m = mass in g
V = volume in cm3
| D = \(\frac{\text{m}}{\text{V}}\) | D = \( m \div V\) |
| \(m = VD\) | \(m = V \times D\) |
| \(V =\frac{\text{m}}{D}\) | \(V = m \div D\) |
Note: If using the formula triangle, it is important to also write out the correct formula in full (both sides of the equals sign) to obtain credit for this in the exam.
If the mass is given in grams (g) and the volume is given in cm3 then the density will have units of g/cm3.
If the mass is given in kilograms (kg) and the volume is given in m3 then the density will have units of kg/m3.
Example
What is the density of a material if 450 cm3 of it has a mass of 200 g?
D = \(\frac{\text{m}}{\text{V}}\)
m = 200 g
V = 450 cm3
D = \(\frac{\text{200~g}}{\text{450~cm}^3}\)
0.44 g/cm3
The density of the material is 0.44 g/cm3.
What is kinetic theory?
Kinetic theory states:
All matter is made up of moving All substances are made of particles. Particles could be atoms, molecules or ions., and these particles can be All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. or A cluster of atoms that are chemically bonded together in a fixed ratio. Molecules are always made from non-metal atoms. A molecule can be represented with a chemical formula, for example, O₂ or CH₄..
The particles are continually moving and if the temperature is raised, the heat energy gives the particles more The energy an object possesses by being in motion. and they move more quickly.
In a solid, the particles are vibrating.
When heated they gain more kinetic energy.
This causes the particles to vibrate more vigorously and the solid expands.
At melting point, particles overcomeThe chemical link that holds molecules together. and the solid turns into a liquid.
When liquid is heated, the particles gain kinetic energy and move faster and further apart.
The liquid expands.
At boiling point, particles overcome bonds and the liquid turns into a gas.
Question
Calculate the mass of oxygen that occupies 0.250 m3 in the liquid state, if the All substances are made of particles. Density is a measure of how close together particles are. Closely packed particles have a higher density than particles that are spread out. of liquid oxygen = 1100 kg/m3.
m = V x p
D = 1100 kg/m3
V = 0.250 m3
m = 0.250 m3 x 1100 kg/m3
m = 275 kg
The mass of 0.250 m3 of oxygen in the liquid state is 275 kg.
Question
Calculate the mass of oxygen that occupies 0.250 m3 in the gas state. (Density of oxygen gas = 1.4 kg/m3)
m = V x p
D = = 1.4 kg/m3
V = 0.250 m3
m = 0.250 m3 x 1.4 kg/m3
m = 0.35 kg
The mass of 0.250 m3 of oxygen in the gas state is 0.35 kg.
Liquid oxygen has much greater mass than an equal volume of oxygen gas because the density of liquid oxygen is very much greater than the density of oxygen gas.
How much do you know about kinetic theory?
More on Unit 1: Density and kinetic theory
Find out more by working through a topic
- count1 of 3
