## Gases: The Empirical Gas Laws - Celcius and Kelvin Temperatures

 In SI Metric the temperature scale is defined as Kelvoin temperature scale. The degree unit is the kelvin (K).  The symbol for the uint is K, not oK.  Kelvin temperatures must be used in many gas law equations in which temperature enters directly into the calculations. The Celcius and kelvin scale are related unit for unit. One degree unit on the Celcius scale is equivalent to one degree unit on the kelvin scale.  The only difference between these two scales is the zero point.  The zero point on the Celcius scale was defined as the freezing point of water, which means that there are higher and lower temperatures around it.  The zero point on the kelvin scale - called absolute zero - corresponds to the lowest temperature that is possible.  It is 273.15 units lower than the zero point on the Celcius scale.  So this means that 0 K equals -273.15oC and 0oC equals 273.15 K. Thermometers are never marked in the kelvin scale. If we need degrees in kelvin the following relationships are to be used. TK =  tc  +  273.15             or       tc  =  TK  -  273.15