Glossary
kelvin
The kelvin is the SI unit of temperature: its zero is absolute zero, its step is the size of a Celsius degree, and kelvin = °C + 273.15.
The kelvin is the SI unit of temperature, and 0 K is absolute zero — the point past which no further motion can be removed from a particle. Its step is the size of a Celsius degree, so a change of 10 degrees Celsius is a change of 10 kelvin, and the two scales differ only in where they start: kelvin = °C + 273.15. Water freezes at 273.15 K and boils at 373.15 K at ordinary pressure, and 37 °C is 310.15 K. The scale earns its place in gas-law arithmetic, because a gas's volume and pressure track the speed of its particles, and only the kelvin scale begins at the temperature where that motion stops. Substituting a Celsius reading for a kelvin one does not produce an answer that looks wrong; it produces a wrong answer that looks ordinary. A temperature and a temperature change are also not the same thing: doubling 10 °C as a change gives 20 °C, and doubling 283 K as an absolute temperature gives 566 K, which is 293 °C.
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Source: NIST periodic table and reference data for the atomic masses and half-life figures, NIH PubChem for the substance data, and NIST Special Publication 811 for the unit conventions — the same sources the chemistry guide cites. All three are US federal government material, not subject to copyright in the United States. Every definition, example and calculation above was written for this course; no dictionary or textbook text is reproduced. (NIST and PubChem accessed 2026-10-26; definitions written 2026-10-27)