Discussion Forum

1)

Gaseous benzene reacts with hydrogen gas in presence of a nickel catalyst to form gaseous cyclohexane according to the reaction.

 $C_{6}H_{6}(g)+3H_{2}(g)\rightarrow C_{6}H_{12}(g)$

A mixture of C₆H₆ and excess H₂ has a pressure of 60mm of Hg in an unknown volume. After the gas had been passed over a nickel catalyst and all the benzene converted to cyclohexane ,the pressure of the gas was 30mm of Hg in the same volume at the same temperature. The fraction of C₆H₆ (by volume) present in the original  volume is 

Answer:

Option D

Explanation:

Let initially ,pressure of C₆H₆ (g) ids  p₁   mm and for H₂(g) is p₂ mm

 p₁+p₂= 60 mm ....(i)

 After the reaction pressure of C₆H₆(g)=0 (as all C₆H₆  has reacted)

 H₂(g)= p₂-3p₁

 So, total pressure =  $p_{2}-3p_{1}+p_{1}=30$mm

 $p_{2}-2p_{1}=30$mm ..........(ii)

 On solving equation (i) and (ii)

 $p_{1}$=10mm, $p_{2}$=50mm

 Fraction of C₆H₆ by volume= moles fraction of pressure =  $\frac{10}{60}=\frac{1}{6}$