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

Work done in a chemical reaction,
`W = Deltan_(0)RT`
Where, `Deltan_(g) =` number of moles of gaseous products - number of moles of gaseous reactants.
combustion of ethane is as follows,
`C_(2)H_(6)(g) + 7/2 O_(2)(g) rarr 2CO_(2)(g) + 3H_(2)O(l)`
`:. Deltan_(g) = 2 - 4.5 = - 2.5`
`W = (2.5mol) (8.31 JK^(-1) mol^(-1)) xx 300 K`
`= 6235.5 k =6.2355 J`
Now , 1 mole of `C_(2)H_(6) = 30g` of `C_(2)H_(6)`
`= 6.2355 kJ`
`:.` Work done for combustion of 90 g of `C_(2)H_(6)`
`= (6.2355 xx 90)/(30)`
`= 18.7065 kJ`
` 18.71 kJ`