science

Liquid carbon dioxide

Liquid carbon dioxide is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Liquid carbon dioxide rather than just read about it. In short: Liquid carbon dioxide is the liquid form of carbon dioxide (CO2). At normal atmospheric pressure, carbon dioxide can only exist as a gas or solid, and is ordinarily found as a trace gas in Earth's atmosphere.

Key takeaways

Liquid carbon dioxide belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Liquid carbon dioxide to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Liquid carbon dioxide from memory before moving on to harder problems.

Reference excerpt

Liquid carbon dioxide is the liquid form of carbon dioxide (CO2). At normal atmospheric pressure, carbon dioxide can only exist as a gas or solid, and is ordinarily found as a trace gas in Earth's atmosphere. Its liquid state can exist at pressures above 5.1 atm (5.2 bar; 75 psi), between the temperatures of its triple point, −56.6 °C (−69.9 °F) and its critical point, 31.1 °C (88.0 °F). Solid CO2, known as dry ice, occurs at low temperatures, and has commercial applications. Dry ice sublimes above −78.5 °C (−109.3 °F) at atmospheric pressure—that is, it transitions directly from solid to gas without an intermediate liquid stage. The uses and applications of liquid carbon dioxide include extracting virgin olive oil from olive paste, in fire extinguishers, and as a coolant. With supercritical carbon dioxide, liquid carbon dioxide is used for decaffeinating coffee.

Properties

Liquid carbon dioxide is a type of liquid which is formed from highly compressed and cooled gaseous carbon dioxide. It does not form under atmospheric conditions. It only exists when the pressure is above 5.1 atm and the temperature is under 31.1 °C (88.0 °F) (temperature of critical point) and above −56.6 °C (−69.9 °F) (temperature of triple point). The chemical symbol remains the same as gaseous carbon dioxide (CO2). It is transparent and odorless, and its density is 1101 kg/m3 when the liquid is at full saturation at −37 °C (−35 °F), decreasing to half that near its critical point. The solubility of water in liquid carbon dioxide is measured in a range of temperatures, ranging from −29 °C (−20 °F) to 22.6 °C (72.7 °F). At this temperature, the pressure is measured in a range from 15 to 60 atmospheres. The solubility turned out to be very low: from 0.02 to 0.10 %.

Uses

Liquid carbon dioxide is used for the preservation of food, in fire extinguishers, and in commercial food processes. For food preservation, liquid carbon dioxide is used to refrigerate, preserve, store, and soften. In a fire extinguisher, the CO2 is stored under pressure as a liquid to act as an anti-flammable. The liquid carbon dioxide not only reduces combustion by displacing oxygen, but also cools the burning surface to avoid further damage. Solvent extraction using compressed liquid CO2 can be used in industrial processes such as removing caffeine from coffee or improving the yield of olive oil production. Liquid carbon dioxide is tested as a means of CO2 transportation for underground or subsea storage purposes. Due to its high density as a liquid, it is much more feasible to ship than as a gas. CO2 is also used in large-scale heat pumps for district heating, replacing less-environmentally-friendly refrigerants. The CO2 changes phases between liquid and gaseous in the process.

See also Other chemical compounds and elements are commonly used for commercial and research purposes in their liquid state:

Liquid oxygen Liquid nitrogen Liquid helium Liquid hydrogen Supercritical carbon dioxide

References

Illustrations

Worked examples

Example 1 — a first encounter with Liquid carbon dioxide

Start with the simplest possible case. Write down what Liquid carbon dioxide claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Liquid carbon dioxide before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Liquid carbon dioxide ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Liquid carbon dioxide

In research: Liquid carbon dioxide appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Liquid carbon dioxide in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Liquid carbon dioxide is common in secondary-school and first-year university syllabi. It links to neighbouring topics Carbon dioxide, so understanding it makes those chapters shorter.
In everyday life: Look for Liquid carbon dioxide outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Liquid carbon dioxide in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Liquid carbon dioxide means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Liquid carbon dioxide out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Liquid carbon dioxide in simple terms?

Why does Liquid carbon dioxide matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Liquid carbon dioxide?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Liquid carbon dioxide.