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Can Oxygen Be Liquid?



Oxygen CAN be a liquid.

Although we mostly think of oxygen as a gas, it can also exist as a liquid. Oxygen makes up 21% of Earth’s atmosphere, and is essential to human respiration. Oxygen is a highly reactive element, and it forms thousands of compounds necessary for organic life. In its gaseous form, oxygen is colorless, odorless, and tasteless. [“Periodic Table of Elements” Los Alamos National Laboratory]

Liquid Oxygen

Pure liquid oxygen rarely occurs in nature, and with good reason. The main difference between a gas and a liquid has to do with atoms: the atoms in a gas are far apart and moving quickly, whereas the atoms in a liquid are closer together and moving slowly. [“States of Matter.” Purdue University] If an element naturally occurs as a gas at room temperature, it must be cooled and pressurized to form a stable liquid. This is the reason liquid oxygen is rare: work is required to create it. At standard atmospheric pressure, oxygen must be cooled to -297.3 degrees Fahrenheit to form a liquid. [“About Cryogenics.” Cryogenics]


One of the most well known uses of liquid oxygen is in rocket engines. A rocket engine is essentially a jet turbine, which requires oxygen to combust fuel. However, in space there is no oxygen, so it must be brought along. If you have ever seen a NASA space shuttle lift off you probably noticed the enormous orange tank strapped to the shuttle. This tank contains liquid hydrogen and liquid oxygen which combust inside the shuttle’s engine. [Liquid Hydrogen–the Fuel of Choice for Space Exploration.” NASA]

Liquid oxygen is also used in a field called cryogenics. Because it is so cold, liquid oxygen is used in scientific experiments where extremely low temperatures are needed, such as the study of superconductivity. [“About Cryogenics.” Cryogenics]



(1)          “Periodic Table of Elements: Los Alamos National Laboratory.” Los Alamos National Laboratory. N.p., n.d. Web. 9 Jan. 2013.

(2)          “States of Matter.” Purdue University – Department of Chemistry. N.p., n.d. Web. 9 Jan. 2013.

(3)          “NASA – Liquid Hydrogen–the Fuel of Choice for Space Exploration.” NASA . N.p., n.d. Web. 9 Jan. 2013.

(4)          “About Cryogenics.” Cryogenics . N.p., n.d. Web. 9 Jan. 2013.

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