Change in State:	Term for change:	Brief Description:
From solid to liquid	Melting	Heat is absorbed into the solid. (endothermic)
From liquid to solid	Freezing	Heat is removed from the liquid. (exothermic)
From liquid to gas	Evaporation	Heat is absorbed into the liquid. (endothermic)
From gas to liquid	Condensation	Heat is removed from the gas. (exothermic)
From solid to gas	Sublimation	Heat is absorbed into the solid. (endothermic)
From gas to solid	Deposition	Heat is removed from the gas. (exothermic)

1.1.4 – Effect of Temperature and Pressure on the Volume of Gas

The volume of a gas in directly proportional to the temperature, and is inversely proportional to the pressure exerted on the gas.

When the temperature of a gas increases, the volume of the gas also increases. When the temperature of the gas decreases, the volume of the gas also decreases.

This is because increase the temperature provides the gas molecules with more kinetic energy, allowing them gas molecules to move further apart from one another, subsequently increase its volume.

When the pressure exerted on the gas increases, the volume of the gas decreases. When the pressure exerted on the gas decreases, the volume of the gas increases.

This is because an increase in pressure causes the gas molecules to come close to each other, hence decreasing the volume of taken up by the molecules.

1.1.5 – Kinetic Particle Theory (Changes of State)

The kinetic particle theory explains the forces and energies between particles. The 4 main assumptions of the theory are:

• All matter is made up of small particles and molecules that cannot be seen by the naked eye.
• All particles have attractive forces pulling them closer together.
• Particles are constantly moving. The higher the temperature, the greater the kinetic energy, and the faster the particles move.
• Given that the temperature is constant, heavier particles travel at slower speeds while lighter particles travel at faster speeds.

According to the kinetic particle theory, solids have very strong attractive forces in pulling the particles close to each other. Meanwhile, liquids have moderately strong attractive forces in between the particles, while gases have weak attractive forces in between the particles. In both solids and liquids, the attractive forces pulling the particles towards each other is greater than the kinetic energy, thus giving them a constant volume. However, in gases, the kinetic energy of each particle is much larger than the attractive forces between them, hence they do not have a constant volume.

The diagram above shows a representation of the particle configuration of each of the 3 states of matter. As seen from the diagram, solids have the least amount of energy in each particle, while gases have the most amount of energy in each particle.

The kinetic particle theory of the change of states can be explained through a heating and cooling curve.

The graph on the left is a heating curve, while the graph on the right is a cooling curve.

In the heating curve, the solid is being heated and its temperature is gradually increasing. As the temperature increases, the particles gain more energy and is able to change states to liquid, before changing to gas later on.

In the cooling curve, the gas is being cooled and its temperature is gradually decreasing. As the temperature decreases, the particles release more energy and changes states to liquid, before changing to solid later on.

When the curve is sloping, it represents a change in temperature of a singular state. When the curve is straight, it represents a change in state (eg. melting, freezing, evaporation, condensation, etc.). During a change of state, the temperature does not increase or decrease as the energy is used up to either break or form intermolecular bonds in between the particles.

Topic 1.1.6 – Kinetic Particle Theory (Gases)

According to the kinetic particle of theory:

• Increasing the temperature of gas particles causes them to move faster, colliding with each other and the walls of their container more often.
• When this collision happens, there is no loss of energy.
• Due to the momentum caused by the change in direction of the particles upon collision with the walls, it exerts a pressure, increasing the volume of the gas.

1.2 – Diffusion

1.2.1 – Kinetic Particle Theory In Diffusion

Diffusion is the process in which different types of substances (liquids and gases all apply) blend in together as a result of their different and random motions.

Diffusion occurs in liquids and gases as these states of matter have particles that are able to move. In liquids, particles are able to slide over one another (flow) while gas particles are able to move freely and randomly. However, diffusion does not occur in solids as the particles are in a fixed state and can only vibrate in its position.

The movement of these particles in diffusion is based on the Brownian motion and the kinetic particle theory. Particles of liquids and gases diffuse until they disperse out evenly to fill up all the available space. In diffusion, particles move from higher densities to lower densities.

The Brownian motion is the random and uncontrolled movements of particles in a fluid as they constantly collide with other particles around them. Since the movement of atoms and molecules in liquids and gases are random, it is given that larger particles will spread out evenly over time. As stated previously, diffusion is one example of the Brownian motion. Examples of brownian motion include:

• The movement of dusts in a room due to air currents.
• Diffusion of pollutants in the air.
• Diffusion of calcium through our bones.

1.2.2 – Effect of Relative Molecular Mass on Diffusion

Generally, diffusion occurs at a much faster rate in gases than in liquids. This is because the molecules in a gas are not held close to one another, unlike in a liquid.

Another thing that affects the rate of diffusion in both liquids and gases are the relative molecular mass of said state of matter. The higher the relative molecular mass, the heavier the particles will be, thus the substance will diffuse at a slower rate. On the other hand, the lower the relative molecular mass, the lighter the particles will be, hence the substance will diffuse at a faster rate. This rule applies to all substances, whether it be elements, compounds or mixtures.

That is all for topic 1 – states of matter. If you would like to check out more of our revision guides, click the link here.

Table of Contents

• Table of Contents – States of Matter
• Topic 1.1 – Solids, Liquids and Gases
  • 1.1.1 – Properties of Solids, Liquids and Gases
  • 1.1.2 – Structures of Solids, Liquids and Gases
  • 1.1.3 – Changes of States
  • 1.1.4 – Effect of Temperature and Pressure on the Volume of Gas
  • 1.1.5 – Kinetic Particle Theory (Changes of State)
  • Topic 1.1.6 – Kinetic Particle Theory (Gases)
• 1.2 – Diffusion
  • 1.2.1 – Kinetic Particle Theory In Diffusion