Given that P, V and T stand for vapour pressure, volume and temperature, an ideal gas obeys the law -PV α T. If the volume is kept constant, P α T. With decreasing temperature the vapour pressure drops, until P = 0 at some temperature T0. Since P cannot be less than zero, or negative, T0 naturally becomes the lowest temperature that we can reach, and can be used as a "natural” lower fixed point while constructing a temperature scale. This is the "absolute zero”, which in the Celsius scale is - 273.150C.
To construct an absolute temperature scale , where the absolute zero is naturally 0. Let us choose the triple point of mercury (-38.80C, at 0.2 mPa) as our upper fixed point, and give assign it a value 100. What will be the boiling point of water on this scale?
159.2
Let the boiling point of water in the near scale be T. Let's list what we know -
We can, therefore, write -