A closed inexpansible vessel contains air saturated with water vapour at 77 degree Celsius.The total pressure in the vessel is 1007mmHg.Calculate the new pressure if the temperature is reduced at 27 degree Celsius (S.V.P of water at 77degree celcius and 27 degree Celsius respectively are 314mmHg and 27mmHg. Treat the air in the vessel as an ideal gas

Answer 1

work this as two problems; air and water.
the air is at 77C and 1007-314 kpa
new air is at P-27 at 27C.
but in each case the moles of air are the same.
n=PV/RT
so P1V/RT1=P2V/RT2 or
P1/T1=P2/T2 where P2=P-27
so
(1007-314)/(77+273)=(P-27)/(27+373) so solve for P, the new total pressure.
Notice this assumes the condensed water does not change the air volume appreciably.