A litre of dry air weighs 1.293 gram at S.T.P Find the temperature at which a litre of air will weigh one gram when the pressure is 72 cm. of mercury.

Answer

`61.4^(@)C`

Explanation

Let us consider 1 gram of air.
At S.T.P. `V_(0) = 1000/1.293 cm^(3)`
`P_(0)76 cm of Hg, T_(0)= 273 K`
Let T be the temperature at which 1 litre of air will weight 1 gram.
`:. V = 1000 c.c., P =72 cm of mercury`
As `(P_(0)T_(0))/(T_0) = (PV)/(T)`
`therfore PV xx T_(0))/(P_(0)V_(0))`
`=(72 xx 1000 xx 273 xx 1.293)/(76 xx 1000)`
`T = 334.4 K = (334.4 - 273)^(@)C`
`= 61.4^(@)C`