Only `N_2,CO and CO_2` gases remain after 0.72 gm of carbon is treated with one litre of air at `27^@C and 4.92` atm pressure.Assume air composition `O_2=20%,N_2=79%,and CO_2=1%` (by volume).The heat evolved (in Kcal) under constant pressure is :
Given : `C+OtoCO_2, DeltaH=-100` Kcal/mol
`C+1/2O_2toCO, DeltaH=-25` Kcal/mol

Answer

Heat evolved = 3 kcal

Explanation

`n_(air)=(4.92xx1)/24.6=0.2` mol
`n_(O_2)=0.2xx0.2=0.04 mol, n_c=0.72/12`
`{:(,C" "+,1/2O_2,toCO),("initial mole",0.06,0.04," " 0),("final mole",0,0.01," "0.06):}`
`{:(,CO" "+,1/2O_2,toCO_2),("initial mole",0.06,0.01," " 0),("final mole",0.04,0," "0.02):}`
Heat evolved =`0.04xx25+0.02xx100=1+2=3 kcal`