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How does dry ice work?

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Quick answer

Dry ice is solid carbon dioxide at about -78.5 °C (-109 °F). It cools things by pulling in heat from its surroundings, which makes its molecules break free of the solid and rise straight into the air as gas, skipping the liquid stage entirely. This process is called sublimation.

Dry ice works by absorbing heat as solid carbon dioxide turns directly into gas, a process called sublimation. Because it skips the liquid stage, it stays extremely cold at about -78.5 °C (-109 °F) and leaves no wet residue.

Step by step

  1. Dry ice starts as solid carbon dioxide frozen at about -78.5 °C (-109 °F) under normal pressure.
  2. Warmer air or objects nearby transfer heat into the solid, raising the energy of its molecules.
  3. That added energy lets molecules break away from the rigid solid lattice instead of melting into liquid.
  4. The freed molecules enter the air as carbon dioxide gas, carrying heat away from the remaining solid.
  5. The solid shrinks and eventually disappears completely, leaving only gas and no puddle.

Key things to understand

  1. Dry ice is solid carbon dioxide, frozen at about -78.5 °C (-109 °F) under normal pressure.
  2. It absorbs heat from warmer surroundings, which breaks the bonds holding its molecules in a solid lattice.
  3. Instead of melting into liquid, the molecules escape straight into the air as carbon dioxide gas, called sublimation.
  4. That escaping gas carries heat away with it, so the remaining dry ice keeps cooling and shrinking.
  5. Because the gas is denser than air, it sinks and can push out oxygen in enclosed spaces, which is a suffocation risk.

Labelled diagram

  1. Solid CO2

    Carbon dioxide frozen at about -78.5 °C, a white block or pellet.

  2. Heat absorbed

    Warm air or an object transfers energy into the solid, exciting its molecules.

  3. Sublimation

    Molecules break free of the solid lattice and escape directly as gas.

  4. Gas sinks

    Carbon dioxide gas is denser than air, so it pools low and can displace oxygen.

  5. No residue

    The solid vanishes completely, leaving no liquid puddle behind.

How dry ice turns into gas

Real-world examples

  • Shipping companies pack frozen food with dry ice pellets so it stays cold without melting into a wet mess.
  • Theatre and concert stages drop dry ice into hot water to make low-lying white fog for special effects.
  • Ice cream vendors use dry ice to keep tubs frozen during transport and to create fog at the point of sale.
  • Laboratories use dry ice mixed with solvents as a cold bath to rapidly chill samples for experiments.

Common mistake

✗ Myth: Dry ice melts into a liquid that then evaporates, like ordinary ice.

✓ Fact: Dry ice never becomes liquid at normal pressure. It sublimes, turning straight from solid to gas, which is why it leaves no puddle and why the gas can build up dangerously in closed rooms.

People also ask

What is dry ice made of?
Dry ice is made of carbon dioxide, the same gas humans exhale and plants absorb. It is frozen solid at about -78.5 °C (-109 °F), far colder than water ice at 0 °C. Unlike water ice, it contains no water at all, which is why it is called dry.
Is dry ice dangerous to breathe?
Yes, in enclosed spaces. Dry ice releases carbon dioxide gas that is denser than air and can push out oxygen, causing dizziness, rapid breathing or unconsciousness. Use it only in ventilated areas, and treat any breathing difficulty as a medical emergency.
How long does dry ice last?
Dry ice sublimates at roughly 2 to 5 kilograms per day in a typical cooler, so a small block may vanish within a day. A thick insulated container slows the process, while a thin box or open air speeds it up considerably.
Why does dry ice fog instead of just disappearing?
The fog you see is not carbon dioxide itself. Cold gas from the dry ice chills nearby water vapour in the air, condensing it into tiny droplets that look like white smoke.
Can you touch dry ice with bare hands?
No. At -78.5 °C it freezes skin cells almost instantly, causing a cold burn similar to frostbite. Handlers use thick insulated gloves or tongs, and anyone injured should see a doctor.
Why does dry ice make a squealing sound when pressed?
Pressing metal against dry ice speeds up sublimation at the contact point. The rush of gas vibrates the metal, producing a high-pitched squeal or scream.
How is dry ice made?
Carbon dioxide gas is compressed and cooled until it becomes a liquid. Releasing the pressure makes some liquid flash into gas, and the sudden cooling freezes the rest into solid dry ice.

Part of the guide: Everyday Science: Light, Heat & Matter →