Gases: Standard Conditions

For gases, standard temperature is considered the freezing point of water, 0˚C.  This causes a problem with mathematical calculations.  Temperature can be positive, negative or 0.  A positive ratio can't equal a negative number, and multiplying or dividing by 0 is 0 or undefined respectively.  To avoid this mathematical problem, the Celsius scale was shifted down to absolute zero. By using linear regression and Charles' Law, it is possible to determine the coldest possible temperature, or  -273.15˚C.

This new scale was called the Kelvin scale in honor of Lord Kelvin.  The gradations of the Kelvin scale are exactly the same as on the Celsius scale, the only difference is that 0 has been shifted to -273.  Therefore there are no negative values on the Kelvin scale.

Temperature is a measurement of the average kinetic energy of the particles of a substance.  If the lowest possible temperature is -273.15˚C, that means that the average kinetic energy must be 0, or that all molecular motion stops.

ALL CALCULATIONS IN GAS LAWS MUST ALWAYS BE CONVERTED TO KELVIN. To convert a Celsius temperature into Kelvin, just add 273.  To convert back from Kelvin to Celsius, just subtract 273.  *Note- by convention the degree symbol is not used for Kelvin.