At constant volume and at 298 K, the heat of combustion of sucrose C12H22O11(s) is -1348.9 kcal/mol. If steam is produced during the combustion, the heat of reaction at constant pressure will be:

The given reaction for combustion is: C12H22O11(s)+12O2(g)→12CO2(g)+11H2O(g);ΔH=-1348.9kcal ∆n=number of moles of products- number of moles of reactants          =(12+11)-12 =11 mol∆H= Heat of reaction at constant pressureΔE =heat of reaction at constant volume; R=0.002kcal;T=298 K. But ΔH=ΔE+ΔnRT                  = -1348.9+(11 x0.002 x298)= -1348.9+6.556                  = -1342.344 k cal