States of matter for OCR GCSE Physics
This page covers the following topics:
4. Particle model and states of matter
5. Changes of state
The particles in a solid are tightly packed in a regular arrangement. They are held together in fixed positions by strong forces, vibrating about those positions. This arrangement of particles is why solids have a fixed shape and volume.
The particles in a liquid are close together with some gaps between them. The particles have enough energy so that they are not held in fixed positions, thus they are not regularly arranged and can slip past each other. This arrangement of particles is why liquids have a fixed volume and take the shape of the container the liquid is placed in.
The particles in a gas are far apart and randomly arranged. The forces between particles are weak enough for the particles to be free to move, and thus they move quickly and randomly in all directions. This arrangement of particles is why gases have the same volume as their container and completely fill it.
Solids have a fixed volume and shape. They also cannot flow due to how the particles are not free to move. Furthermore, they cannot be easily compressed, since the spaces between the tightly packed particles are small. Liquids have a fixed volume and take the shape of their container. Since the particles of a liquid can move around, they can flow and take the shape of their container. Liquids can also not be easily compressed, since the particles are close together. Gases do not have a fixed shape or volume, as they fill up their container. Since particles of gases can move quickly and randomly in all directions, gases can flow. Unlike the other two states of matter, gases can be compressed, since the particles are far apart from each other.
The state of a material can be changed by adding or removing energy. Solids can be melted into liquids when heated, which in turn will evaporate into gas. Condensation will occur when a gas is cooled into a liquid, which in turn will freeze into a solid. Sublimation is when a solid becomes a gas when heated, without becoming a liquid first. A heating or cooling curve is a graph that shows the temperature of a material against the energy it has absorbed. When a material is changing state, the curve will flatten out, since the temperature will stay the same until the change of state has finished.
Label the given cooling curve.
A: gas. B: condensation. C: liquid. D: freezing. E: solid.
A liquid undergoes freezing. Explain what this means.
Energy is removed from the liquid, which freezes it into a solid.
Explain how the particles in a gas move.
The particles in a gas are free to move quickly and randomly in all directions.
A small amount of ethanol is poured into a measuring cylinder. Explain what happens to the ethanol's shape and volume.
The volume of ethanol will remain fixed. The ethanol will take the shape of the measuring cylinder.
Can a liquid of volume 70 cm³ be compressed into a syringe of volume 20 cm³? Explain.
Liquids cannot be easily compressed, since the particles are close together. So, the liquid cannot be squeezed into the syringe.
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