Only `N_(2)` and `CO_(2)` gases remain after 15.5 g of carbon is treated with 25 litres of air at `25^(@)C` and 5.5 atm pressure. Assume air of composition: `O_(2)-19%,N_(2)-80%` and `CO_(2)-1%` (by volume). Calculate the heat evolved under constant pressure Given,
`C+O_(2) to CO_(2),DeltaH=-94.05"kcal/mole"`
`C+(1)/(2)O_(2) to CO,DeltaH=-26.41"kcal/mole"`

Explanation

Moles of `C=(15.5)/(12)=1.292`
Moles of `O_(2)=(pV)/(RT)=(5.5xx(0.19xx25))/(0.0821xx298)=1.068`
`C+O_(2) to CO_(2)`
x moles (say) x moles
`C+(1)/(2)O_(2) to CO`
`(1.292-x)"moles" (1.292-x)"moles"`
As `O_(2)` is fully consumed,
number of moles of O before reaction
= number of moles of O after reaction
=moles of O in `CO_(2)+"moles"` of O in CO
or `2xx1.068=2x+(1.292-x)`
or `x=0.844`
Mole of `CO_(2)=0.844`
Mole of `CO=1.292-0.844=0.448`.
Total heat evolved `=0.844(-94.05)+0.448(-26.41)=-91.2"kcal"`