Liquid vs. Gas: What's the Difference?
Both flow, but they differ in how their particles are spaced and whether they keep a fixed volume. In a liquid, particles are close together, so it keeps a fixed volume and just changes shape to fit its container. In a gas, particles are far apart and move freely, so it has no fixed volume — it spreads out to fill any space and can be squeezed into a smaller one. Heat a liquid enough and it boils into a gas.
See the difference, explained visually.
Watch a 2-minute animated lesson comparing liquid and gas.
At a glance
| Liquid | Gas | |
|---|---|---|
| Volume | Fixed | No fixed volume — fills the space |
| Shape | Takes its container's shape | Fills the whole container |
| Particles | Close together | Far apart, moving fast |
| Compressible? | Almost not at all | Easily compressed |
| Example | Water | Steam / air |
Which should you use?
Liquid
It's a liquid when it keeps a fixed volume and pools at the bottom of its container — like water in a glass.
Gas
It's a gas when it spreads out to fill all the space available and can be compressed — like air or steam.
Frequently asked questions
- What's the key difference between a liquid and a gas?
- A liquid has a fixed volume and only changes shape; a gas has no fixed volume and spreads to fill any space. That's because a gas's particles are far apart, while a liquid's stay close together.
- Why can a gas be compressed but a liquid can't?
- A gas is mostly empty space between far-apart particles, so squeezing pushes them closer. A liquid's particles are already packed close together, leaving almost no room to compress.
- How does a liquid turn into a gas?
- By evaporation (at the surface) or boiling (throughout). Adding heat gives the particles enough energy to break free of each other and spread out as a gas.