Intermediate Topic 620 of 1102 Inorganic Chemistry
Heavy Water
D2O, used as a moderator in some nuclear reactors.
In-depth explanation of Heavy Water
Heavy water, D2O, has both hydrogen atoms replaced by deuterium, giving a molar mass of about 20.03 g/mol instead of 18.02 g/mol. Its density is about 1.107 g/mL at 25 degrees C, and its melting and boiling points, 3.8 degrees C and 101.4 degrees C, are higher than those of ordinary water. Its chemistry is similar to that of H2O, but reactions involving O-D bonds are slower because of the kinetic isotope effect. It is used as a neutron moderator in some reactors, such as CANDU designs, because deuterium absorbs far fewer neutrons than hydrogen does. Replacing a large fraction of body water with D2O is harmful.
Going deeper: Heavy Water
Key ideas: D2O has molar mass 20.03 g per mol, density 1.107 g per mL, freezing point 3.8 C and boiling point 101.4 C. It is made by repeated electrolysis or by the Girdler sulfide exchange process, exploiting small differences in exchange equilibria. Its low neutron absorption makes it an ideal moderator in CANDU reactors that run on natural uranium.
Common mistakes and connections: Heavy water is not radioactive; confusing it with tritiated water is a common error. It is also not harmless in bulk, since replacing most body water disrupts enzyme kinetics. Students forget that the moderator slows neutrons but does not absorb them, unlike control rods. Related to isotopes of hydrogen and nuclear fission.
Visualization of Heavy Water
Molar mass of ordinary water compared with heavy water D2O; the extra neutrons make D2O about 11 percent heavier, with a density of 1.107 g/mL. The interactive lesson shows this as a live animation or chart.
Worked example and use case
CANDU reactors can run on natural uranium because heavy water slows neutrons without absorbing many of them.
Frequently asked questions about Heavy Water
What is Heavy Water?
D2O, used as a moderator in some nuclear reactors.
Is Heavy Water a beginner, intermediate or advanced topic?
Heavy Water is a intermediate topic in Inorganic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Heavy Water?
Study these earlier topics in Inorganic Chemistry first: Isotopes of Hydrogen, Hydrides, Water Chemistry.
What comes after Heavy Water?
The next topics in Inorganic Chemistry are Hydrogen Peroxide and Alkali Metals.
Can I practise Heavy Water with quizzes?
Yes. The interactive lesson includes a self-check question on Heavy Water, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Heavy Water fits in Inorganic Chemistry
Heavy Water is topic 5 of 113 in Inorganic Chemistry.