How do you convert from Kelvin to Fahrenheit?
Take away 273.15, multiply by 1.8, then add 32. The first step turns kelvin into Celsius and the rest is the usual Celsius-to-Fahrenheit sum.
A warm lab at 300 K: 300 - 273.15 = 26.85, × 1.8 = 48.33, + 32 = 80.33°F. Water boils at 373.15 K, which comes out at exactly 212°F.
There's no mental shortcut worth having, because the two scales start from different zeros. Absolute zero, 0 K, is -459.67°F, which is about as cold as Fahrenheit gets.
About Kelvin
Kelvin is an absolute temperature measurement defined in the International System of Units (SI). It is named after the Scottish physicist William Thomson (Lord Kelvin) who studied the field of thermodynamics. The Kelvin scale is based on absolute zero; the point at which all molecular motion ceases.
Unlike most other temperature scales, Kelvin does not have degrees as it is not a relative scale. The Kelvin scale is often used in physics, chemistry, and cosmology.
One advantage of Kelvin is that it does not have negative values making some calculations easier. This is useful in science calculations involving gases as it relates to the kinetic energy of molecules.
About the Fahrenheit scale
Fahrenheit is a relative temperature scale created by the Polish-German physicist Daniel Gabriel Fahrenheit. It is mainly used in the United States and is less common in science compared to the Celsius (or Centigrade) scale.
Fahrenheit is based on the freezing and boiling points of water at standard atmospheric pressure with 32°F at freezing point and 212°F at boiling point.
Whilst Fahrenheit is still commonly used in the United States it is important to note that most of the world relies on Celsius.
What happens at absolute zero (0K)?
At absolute zero, 0 Kelvin (0K) or -273.15 degrees Celsius, the temperature is at the lowest possible point anything can possibly be. At this temperature the kinetic energy of atoms and molecules is zero causing them to come to a complete standstill. All molecular motion ceases and matter becomes still.
Several amazing phenomena occur here. As there is no molecular motion there is no heat energy and this has significant implications for the physical properties of the substance. For example, materials become very brittle and their electrical resistance becomes zero. Gases and liquids freeze into solids.
Scientists have never cooled anything down to absolute zero. However they have been able to see the effects of approaching absolute zero. This has provided insights into the behavior of matter and have led to the understanding of superconductors and Bose-Einstein condensates.
Why is Kelvin quoted as K and not °K?
This abbreviation of K is based on the fact that Kelvin is an absolute temperature scale where zero Kelvin (0K) is absolute zero. Celsius and Fahrenheit which have arbitrary zero points based on freezing and boiling points of water are relative and have degrees of relation whereas the Kelvin scale is based on the absolute thermodynamic temperature.
By omitting the degree symbol, it reminds us that Kelvin is not a relative measurement but a unit of measurement on its own. The use of "K" instead of "°K" for Kelvin was decided as an SI convention to reserve the degree symbol for relative temperature scales.
Why can't you get a negative Kelvin value?
Kelvin is an absolute measurement of temperature meaning it starts at absolute zero, the lowest possible temperature in our universe. Absolute zero is 0 Kelvin(K) or -273.15 degrees Celsius(°C). The Kelvin scale is based on the average kinetic energy of particles in a substance.
You cannot have a negative Kelvin value because at 0K there is no kinetic energy in the particles and are at their lowest possible state of motion. It is impossible for a system to have less energy than zero.
Negative Kelvin would imply that a system has a negative thermal energy which breaks the principles of thermodynamics. It is important to remember that negative temperatures exist in other temperature scales such as the Celsius and Fahrenheit.