problem1) 1.5 kg of Oxygen (N2) and 0.15 kg of Helium (He₂) are separated by the partition in the vessel.  Nitrogen is at 5 bar and 90^°C and the Helium at 1 bar and 20^°C.  Partition is removed and the gases are allowed to mix.
Find:
a) the mass fraction, mole fraction and mean molecular weight of the mixture,
b) the temperature and pressure after mixing,
c) the entropy change in the mixing process.
The c_v values for Oxygen and Helium are 0.665 kJ/kgK and 3.116 kJ/kgK respectively.  (O₂ has the molecular weight of 32; He₂ has molecular weight of 4).

problem2) The humidity of air could be determined by the use of two different thermometers; a ‘dry bulb’ thermometer and a ‘wet bulb’ thermometer.  With reference to a suitable text book, describe how these thermometers can be used to estimate the amount of water vapour in the air.
Describe one other method of measuring the humidity of the atmosphere.