Question

Liquid benzene $\left( C _{6} H _{6}\right)$ bums in oxygen according to $2 C _{6} H _{6}( l )+15 O _{2}( g ) \longrightarrow 12 CO _{2}( g )+6 H _{2} O ( g )$ How many litres of $O _{2}$ at STP are needed to complete the combustion of $39\, g$ of liquid benzene?

• A. 74 L
• B. 11.2 L
• C. 22.4 L
• D. 84 L

Answer 1

Answer: (D)

$2 C _{6} H _{6}( l )+15\, O _{2}( g ) \longrightarrow 12\, CO _{2}( g )+6 H _{2} O ( g )$
$2 \times 78\, g\,\,\,\, 15 \times 22.4\, L$
From equation $15 \times 22.4\, L$ of $O _{2}$ is required for $=156\, g$ of benzene
i.e., $156\, g$ benzene for complete combustion required $O _{2}( STP )=15 \times 22.4\, L$
$39\, g$ benzene for complete combustion required
$O _{2}( STP )=\frac{15 \times 22.4}{156} \times 39=84\, L$ of $O _{2}$