CAIE IGCSE Chemistry
1.1 Solids, liquids and gases
Notes
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State the distinguishing properties of solids, liquids and gases
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The three states of matter are solid, liquid and gas
Solid: Particles are closely packed and have a fixed arrangement
Liquid: Particles are close together but have a random arrangement
Gas: Particles are spread apart and have a random arrangement
Describe the structures of solids, liquids and gases in terms of particle
separation, arrangement and motion
● Solid: Particles hold a regular arrangement and have the least amount of
energy. The particles vibrate in fixed positions. Cannot be compressed.
● Liquid: Particles are arranged randomly and close together. The particles are
able to move past each other and take the shape of their container. Cannot be
compressed.
● Gas: Particles are arranged randomly and have the most energy. The
particles in a gas are relatively spread out and move randomly in all
directions. Can be compressed.
Describe changes of state in terms of melting, boiling, evaporating,
freezing and condensing
● Physical changes: Involves the forces between the particles of the substances
o Melting: Solid to liquid
o Boiling: Liquid to gas. Bubbles of gas will form throughout the liquid,
rising to the surface to evaporate into the surroundings.
o Evaporation: Liquid to gas. The particles of gas formed will escape
from the surface of the liquid only.
o Freezing: Liquid to solid
o Condensation: Gas to liquid
o (Sublimation: Solid to gas)
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● Melting and freezing take place at the melting point
● Boiling and condensing take place at the boiling point
Describe the effects of temperature and pressure on the volume of a gas
● As temperature increases, the volume of a gas will increase
● As pressure increases, the volume of a gas will decrease
● As pressure decreases, the volume of a gas will increase
(Extended only) Explain changes of state in terms of kinetic particle theory,
including the interpretation of heating and cooling curves
● Kinetic particle theory models the three states of matter by representing the
particles as small solid spheres; it can be used to explain melting, boiling,
freezing, condensing and sublimation.
● For melting, boiling and evaporation: heat (thermal energy) must be
transferred into kinetic energy in the particles, so they gain enough energy to
overcome the intermolecular forces. For instance, forces of attraction between
solid particles in the rigid arrangement are overcome through melting, so
liquid particles are able to spread apart and move around.
● For freezing and condensing: Energy is lost from the particles in the
substance. Intermolecular forces are formed between the particles, holding
the particles closer together
● The more kinetic energy particles have, the more movement, which causes a
change of state from (s) to (l) to (g)
● A heating curve is a graph that shows the temperature against time as a solid
changes state to a liquid to a gas
○ As the temperature rises, the particles gain more energy, overcoming
the forces of attraction between the particles
○ The line then becomes flat (plateau) as the solid changes state to a
liquid (melting). The temperature at which this process occurs is called
the melting point.
○ Once all the solid has melted, the temperature will increase again,
increasing the energy further
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○ Again, the line will become horizontal again as the liquid boils and the
forces of attraction between the liquid particles are broken and
changes state to a gas. This temperature is the boiling point.
○ The temperature will continue to rise once all liquid has boiled.
● A cooling graph is a graph that shows the temperature against time as a gas
is cooled to a liquid to a solid
○ At the start of the graph, the substance is still in the gaseous state, but
the temperature decreases as energy is lost into the surroundings
○ The line then plateaus, new bonds are formed between the gas
particles, turning them to liquid through condensation
○ The temperature decreases further as soon as all the gas particles
have turned to liquid.
○ The line becomes horizontal again as the freezing point is reached and
more bonds are formed, changing liquid to solid state
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(Extended only) Explain, in terms of kinetic particle theory, the effects of
temperature and pressure on the volume of a gas
● As temperature increases, the volume of a gas will increase:
○ Increasing the temperature increases the kinetic energy of the gas
particles, so the gas particles move and collide with the container more
quickly, spreading further apart.
● As pressure increases, the volume of a gas will decrease:
○ Pressure refers to the number of particles in a fixed volume.
○ Increasing the pressure decreases the volume of the gas, as the gas
particles are forced closer together.
○ Decreasing the pressure increases the volume of the gas, as the gas
particles can spread further apart.
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