Question

Place the following substances in order of increasing vapor pressure. 

H₂O N₂ CO 

• H₂O < CO < N₂ 

• N₂ < H₂O < CO 

• Na < CO < H₂O 

• CO < N₂ < H₂O 

• CO < H₂O < N₂ 

Answer 1

Answer is option 1)H₂O2

Because water molecule has strong extensive hydrogen bonds and much energy is needed to break these bonds and so the number of molecules at vapour state will decrease and thus vapour pressure decreases.In the case of carbon monoxide ,it has a strong triple bond in its structre and which consist of both sigma and pi bonds.So in comparison with Nitrogen CO has stronger bonds and polarity.In N₂,only triple bond is present but the molecule is non-polar in nature.

In addition to this we know that water is a liquid and other 2 are gases in nature.Their boiling points shows the opposite trend.H₂O(100⁰c)>CO(-191.5⁰c)>N₂(-195.8⁰c)

According to boiling point definition ,B.P is the temperature at which liquid boils to form vapours .As B.p increases the more energy is needed for the formation of vapour.So here water needs highest energy and so shows lowest vapour pressure.and vice versa for N₂.CO shows middle range behavior in B.p and V.P.