science

Liquid oxygen

Liquid oxygen 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 oxygen rather than just read about it. In short: Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear, pale cyan liquid form of dioxygen O2. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H.

Key takeaways

Liquid oxygen 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 oxygen to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Liquid oxygen from memory before moving on to harder problems.

Reference excerpt

Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear, pale cyan liquid form of dioxygen O2. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an application which is ongoing.

Physical properties Liquid oxygen has a clear, pale cyan color and is strongly paramagnetic: it can be suspended between the poles of a powerful horseshoe magnet. Liquid oxygen has a density of 1.141 kg/L (1.141 g/ml), slightly denser than liquid water, and is cryogenic with a freezing point of 54.36 K (−218.79 °C; −361.82 °F) and a boiling point of 90.19 K (−182.96 °C; −297.33 °F) at 1 bar (14.5 psi). Liquid oxygen has an expansion ratio of 1:861 and because of this, it is used in some commercial and military aircraft as a transportable source of breathing oxygen. Liquid oxygen is also a very powerful oxidizing agent: organic materials will burn rapidly and energetically in liquid oxygen. Further, if soaked in liquid oxygen, some materials such as coal briquettes, carbon black, etc., can detonate unpredictably from sources of ignition such as flames, sparks or impact from light blows. Petrochemicals, including asphalt, often exhibit this behavior. The tetraoxygen molecule (O4) was predicted in 1924 by Gilbert N. Lewis, who proposed it to explain why liquid oxygen defied Curie's law. Modern computer simulations indicate that, although there are no stable O4 molecules in liquid oxygen, O2 molecules do tend to associate in pairs with antiparallel spins, forming transient O4 units. Liquid nitrogen has a lower boiling point at −196 °C (77 K) than oxygen's −183 °C (90 K), and vessels containing liquid nitrogen can condense oxygen from air: when most of the nitrogen has evaporated from such a vessel, there is a risk that liquid oxygen remaining can react violently with organic material. Conversely, liquid nitrogen or liquid air can be oxygen-enriched by letting it stand in open air; atmospheric oxygen dissolves in it, while nitrogen evaporates preferentially. The surface tension of liquid oxygen at its normal pressure boiling point is 13.2 dyn/cm (13.2 mN/m).

Uses

In commerce, liquid oxygen is classified as an industrial gas and is widely used for industrial and medical purposes. Liquid oxygen is obtained from the oxygen found naturally in air by fractional distillation in a cryogenic air separation plant.

Air forces have long recognized the strategic importance of liquid oxygen, both as an oxidizer and as a supply of gaseous oxygen for breathing in hospitals and high-altitude aircraft flights. In 1985, the USAF started a program of building its own oxygen-generation facilities at all major consumption bases.

In rocket propellant

Liquid oxygen is the most common cryogenic liquid oxidizer propellant for spacecraft propulsion applications, usually in combination with liquid hydrogen, kerosene or methane. Liquid oxygen was used in the first liquid fueled rocket. The World War II V-2 missile also used liquid oxygen under the name A-Stoff and Sauerstoff. In the 1950s, during the Cold War both the United States' Redstone and Atlas rockets, and the Soviet R-7 Semyorka used liquid oxygen. Later, in the 1960s and 1970s, the ascent stages of the Apollo Saturn rockets, and the Space Shuttle main engines used liquid oxygen. As of 2026, many active rockets use liquid oxygen:

Chinese space program CASC: Long March (rocket family) operational: Long March -5, -5B, -6, -6A, -6C, -7, -7A, -8, -8A, -10B, -12, -12A, -12B under development: -9, -10, -10A CAS Space: Kinetica 2 Deep Blue Aerospace: Nebula-1 (under development) Galactic Energy: Pallas-1 (under development) i-Space: Hyperbola-3 (under development) LandSpace: Zhuque-2E, Zhuque-3 Orienspace: Gravity-2 (under development) Space Epoch: Yuanxingzhe-1 (under development) Space Pioneer: Tianlong-2, Tianlong-3 Europe European Space Agency: Ariane 6 Isar Aerospace: Spectrum (under development) PLD Space: Miura 5 (under development) Rocket Factory Augsburg: RFA One (under development) Indian Space Research Organisation: GSLV, LVM3 JAXA (Japan): H3 Korea Aerospace Research Institute: Nuri Roscosmos (Russia): Soyuz-2, Angara, Soyuz-5 United States Blue Origin: New Glenn Firefly Aerospace: Firefly Alpha NASA: Space Launch System Northrop Grumman: Antares 300 (under development) Relativity Space: Terran R (under development) Rocket Lab: Electron, Neutron (under development) SpaceX: Falcon 9, Falcon Heavy, Starship Stoke Space: Nova (under development) United Launch Alliance: Atlas V, Vulcan

History By 1845, Michael Faraday had managed to liquefy most gases then known to exist. Six gases, however, resisted every attempt at liquefaction and were known at the time as "permanent gases". They were oxygen, hydrogen, nitrogen, carbon monoxide, methane, and nitric oxide. In 1877, Louis Paul Cailletet in France and Raoul Pictet in Switzerland succeeded in producing the first droplets of liquid air. In 1883, Polish professors Zygmunt Wróblewski and Karol Olszewski produced the first measurable quantity of liquid oxygen.

Illustrations

Liquid oxygen: When liquid oxygen (O2) is poured from a beaker into a strong magnet, the oxygen is temporarily suspended between the magnet poles, owing to its paramagnetism. — When liquid oxygen (O2) is poured from a beaker into a strong magnet, the oxygen is temporarily suspended between the magnet poles, owing to its paramagnetism.

Worked examples

Example 1 — a first encounter with Liquid oxygen

Start with the simplest possible case. Write down what Liquid oxygen 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 oxygen 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 oxygen 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 oxygen

In research: Liquid oxygen 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 oxygen 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 oxygen is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1883 in science, Cryogenics, Industrial gases, so understanding it makes those chapters shorter.
In everyday life: Look for Liquid oxygen 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 oxygen in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Liquid oxygen 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 oxygen out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Liquid oxygen in simple terms?

Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear, pale cyan liquid form of dioxygen O2. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H.

Why does Liquid oxygen 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 oxygen?

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 oxygen.