The work done during combustion of `9 xx 10^(-2)` kg of ethane, `C_(2)H_(6)(g)` at 300 K is (Given R=8.314 J `deg^(-1) mol^(-1)`, atomic mass C = 12, H=1)

Options

A. 6.236 kJ
B. `-6.236` kJ
C. 18.71 kJ
D. `-18.71` kJ

Answer

C

Explanation

Ethane on combustion gives `CO_(2)` and `H_(2)O` as
`C_(2)H_(6)(g) + 7/2 O_(2)(g) to 2CO_(2)(g) + 3H_(2)O(l)`
`Deltan = sumn_(g)("product") - sum n(g) ("reactant")`
`=(2)-(1+3.5) = -2.5`
W=`-Deltan RT`
`=(-2)(-2.5) xx 8.314 xx 300`
`=625.55` J
`=6.2355` kJ
The molar mass of `C_(2)H_(6)` is =30 g mol
For 30 g, `W=+6.2 355` kJ
For 90g, `W = 3 xx 6.2355 kJ = 18.71` kJ