Matter and Reactions
States of Matter & Gas Laws
13 min · 2 worked examplesFree
Solid, liquid and gas as arrangements of particles, and the gas law that relates pressure, volume and temperature.
After this lesson you can
- Use pV = nRT with consistent units
- Predict what happens when you squeeze or heat a gas
- Say where the ideal gas model stops being trustworthy
Three states
In a solid, particles are closely packed in fixed positions, vibrating but not moving past each other, so a solid holds its shape.
In a liquid, particles are still close but free to slide, so a liquid takes the shape of its container while keeping its volume.
In a gas, particles are far apart and move fast and independently, so a gas fills whatever space it is given. That spacing is why gases are compressible and liquids essentially are not, a fact hydraulics depends on entirely.
Changing state does not change the substance, only the arrangement. Melting and boiling absorb energy to overcome the forces between particles, which is why a temperature reading sits still while ice melts even though heat is being added.
In the full lesson
- Three states
- The ideal gas law
- Where the model breaks
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