Solids, Liquids, and Gases
Introduced| English | Meaning |
|---|---|
| kinetic energy/kɪˈnetɪk ˈenədʒi/ | The energy an object has because of its motion. |
| phase change/feɪz tʃeɪndʒ/ | A transition between physical phases, such as melting, boiling or condensation. |
Three faces of matter
- The same water can be ice, a puddle, or steam.
- Only the temperature changed, not the molecules.
- What differs is how the particles are packed and how they move.
- Heat sets the pace; attractions set the order.
Packed, flowing, free
- In a solid, particles are locked in a fixed, ordered pattern, only vibrating.
- In a liquid, particles touch but are free to slide past each other.
- In a gas, particles are far apart, moving fast and freely.
Particles are packed in a solid, close but mobile in a liquid, and far apart in a gas
In which state are particles far apart and moving fast and freely?
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Gas particles are widely spaced and move freely.
Heating climbs the ladder
- Adding heat raises the kinetic energy 动能 and loosens the particles.
- Solid becomes liquid becomes gas as heat overcomes the attractions.
- A phase change 相变 happens at a fixed temperature.
During a phase change, the temperature stays constant.
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Added heat breaks attractions instead of raising the temperature.
Order the states from LOWEST to HIGHEST particle energy.
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Heating adds energy, so solid < liquid < gas.
Temperature versus attraction
- Strong attractions (intermolecular forces) favour the solid and liquid states.
- High temperature favours the gas state.
- The balance of the two sets the state at any moment.
Solid, liquid, gas
Raise the temperature and watch particles gain energy and break free from solid to liquid to gas.
A substance stays solid or liquid rather than gas when...
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Strong attractions hold particles together against thermal motion.
Why is oxygen a gas but water a liquid at room temperature?
- Water has strong hydrogen bonds holding its molecules together.
- Oxygen has only weak dispersion forces, too weak to stay liquid at room temperature.
Which state keeps a fixed volume but takes the shape of its container?
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A liquid keeps its volume but not its shape.
Water is a liquid at room temperature largely because of strong ____ bonds.
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Hydrogen bonds hold water molecules together as a liquid.
During a phase change the temperature stays constant — the added heat breaks attractions rather than speeding the particles up. The molecules themselves are unchanged across states; only their arrangement and motion differ. A gas fills its container, a liquid keeps its volume but not its shape, and a solid keeps both.
Solid, liquid, and gas differ only in how particles are packed and how fast they move. Adding heat raises the kinetic energy until a phase change frees the particles. Strong intermolecular forces favour solids and liquids; high temperature favours gases, and the balance sets the state.