Gaseous benzene reacts with hydrogen gas in presence of a nickel catalyst to form gaseous cyclohexane according to the reaction C6H6(g)+3H2(g) arrow C6H12(g) A mixture of C6H6 and excess H2 has a pressure of 60 mm 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 30 mm of Hg in the same volume at the same temperature. The fraction of C6H6 (by volume) present in the original volume is

Question

Gaseous benzene reacts with hydrogen gas in presence of a nickel catalyst to form gaseous cyclohexane according to the reaction C6H6(g)+3H2(g) arrow C6H12(g) A mixture of C6H6 and excess H2 has a pressure of 60 mm 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 30 mm of Hg in the same volume at the same temperature. The fraction of C6H6 (by volume) present in the original volume is (A) 1/3 (B) 1/4 (C) 1/5 (D) 1/6

Tardigrade Admin · Accepted Answer

Let, initial pressure of C6H6(g) = P1 mm and that of H2(g) = P2 mm ∴ P1+P2=60 mm ...(i) After the reaction, pressure of C6H6(g) = 0 (as all has reacted) pressure of H2(g) = P2 - 3P1 pressure of C6H12(g) = P1 Total pressure = P2 - 3P1 + P1 = 30 mm or P2 - 2P1 = 30 mm ...(ii) Solving (i) and (ii), we get P1 = 10 mm, P2 = 50 mm Fraction of C6H6 by volume = Fraction of moles = Fraction of pressure =(10/60)=(1/6)

$1/3$

$1/4$

$1/5$

$1/6$