The molar heat of formation of nh4no3 (s) is -367.54 kj and those of no2(g) is 81.46and h2o(l) is -285.78 kj at 298k and 1.0 atmospheric pressure .Calculate delta H and delta U for the reaction.
Dear Student,
The molar heat of formation of NH4NO3 = -367.54 kJ
The molar heat of formation of N2O = 81.46 kJ
The molar heat of formation of H2O = -285.78 kJ
The chemical reaction of formation of NH4NO3 is as follow:
N2O + 2H2O → NH4NO3
Enthalpy of reaction = ΔHf (NH4NO3) - [ΔHf (N2O) + 2 ΔHf(H2O)]
Enthalpy of reaction = -367.54 - [81.46 + 2×(-285.78)]
Enthalpy of reaction = -367.54 - [81.46 -571.56]
Enthalpy of reaction = ΔH = -367.54 + 490.10
Enthalpy of reaction = ΔH =122.56 kJ = 122560 J
As we know that,
ΔH = ΔU + (Δn) RT
(Δn) = 1-3 = -2
R= 8.314 JK-1 mol-1
T = 298 K
Putting all the values in the relation:
122560 = ΔU +(-2) × 8.314 ×298
ΔU = 122560 + 16.628 ×298
ΔU = 127515.14 J