Change of State

According to the kinetic theory of matter (also known as the particle theory), all matter is made up of many very small particles that are constantly moving. The movement of these particles is influenced by the amount of energy they have and their interactions with one another. These particles can be atoms, molecules, or ions, and they are in continual motion.

The kinetic theory helps explain the properties and behaviors of materials by providing a model of what happens at the particle level. It allows us to visualize how materials behave in different states and during physical changes, such as melting or boiling.

1. Solids:
   1. The particles are tightly packed and strongly attracted to each other. They are in fixed positions but vibrate.
   2. Solids have a definite shape and maintain that shape.
   3. They are difficult to compress because the particles are already closely packed together.
   4. Solids are often dense because the particles are packed tightly together.
2. Liquids:
   1. The particles are fairly close together, with some attraction between them. The particles are able to move around in all directions, but their movement is limited by attractions between them.
   2. Liquids do not have a definite shape, but they flow and fill the bottom of a container. They maintain a constant volume unless the temperature changes.
   3. Liquids are difficult to compress because there are many particles in a small volume.
   4. Liquids are often dense because their particles are closely packed together.
3. Gases:
   1. The particles have little attraction between them and are widely spaced apart. They are free to move in all directions, colliding with each other and with the walls of the container.
   2. Gases do not have a definite shape and expand to fill any container.
   3. Gases are easily compressed because there are very few particles in a large volume.
   4. Gases are often low in density because there are not many particles in a large space.

The kinetic theory of matter helps explain what happens during physical changes:

1. Melting: When a solid is heated, the particles gain energy and vibrate more. If enough energy is supplied, the particles overcome their fixed positions and the solid changes to a liquid.
2. Boiling: In a liquid, when enough heat is supplied, the particles gain enough energy to overcome the attractions between them and change into a gas.
3. Evaporation: Even at temperatures below boiling point, some particles at the surface of a liquid may have enough energy to escape into the air as gas.

The graph of temperature versus temperature for a Heated.

Melting, is the process of change of the state of matter from solid into liquid e.g ice into water.

Melting point (M.P): Itis the temperature at which solid substance tends to change into liquid.

Freezing: It is the process of change of the state of matter from liquid to solid e.g water into ice.

Freezing point: Is the temperature at which liquid change into solid. E.g water change into ice at OºC.

Evaporation: Is the process of change liquid substance into vapour (gas)

Sublimation: It is the change of state of matter from solid to gas and vice versa without passing through the liquid phase. e.g. Ammonium Chloride ( NH4CL) and Iodine tends to sublime.

Sublimation point is the temperature at which a solid tends to change into gas and vice versa without passing through liquid state.

Condensation: Is the change of state of gaseous state of matter into liquid state.e.g steam into water.

Deposition: Is the change of the state matter from gas into solid. e.g. Ammonium chloride vapor and Iodine vapor into solid (NH4CI) and (Iodine).

Demonstration of cooling and melting curves for (octadecanoic acid).

When an impurity is added to a substance, its boiling point increases (elevated boiling point). This is because the addition of the solute lowers the vapor pressure of the solution compared to the pure solvent. As a result, more heat is required to make the vapor pressure of the solution equal to the atmospheric pressure. This increase in required heat causes the boiling point to rise.

For example:

The boiling point of pure water is 100°C under normal atmospheric pressure. When an impurity is added, the boiling point of water will increase, depending on the concentration of the impurity.

When an impurity is added to a substance, its freezing point decreases (lowered freezing point). The addition of the solute lowers the vapor pressure of the solution compared to the pure solvent. Since freezing occurs when the vapor pressure of the liquid and solid phase are equal, this will happen at a lower temperature for a solution than for the pure solvent.

For example:

The freezing point of pure water is 0°C under normal atmospheric pressure. When an impurity is added, the freezing point of water will decrease.