I'm trying to estimate the energy reliefs for 1.0 kg of ammonia gas scrubbing in 60% nitric acid solution.
Heat of dilution for NH4NO3 aq. sol. can be retrieved from: "International Critical Tables", Vol. V, 1929, p. 162.
Dear Michael: please note that, considering Hess's law, we get the same final thermodynamic state, by either considering the neutralization of NH4OH (aq) with HNO3 (aq); or by considering the same moles of NH4NO3 as directly dissolved in water, for equal final concentration. The signalled thermochemical data concerns to last path.
Dear Michael:
We can calculate the enthalpy that would correspond to NH4NO3 (aq), at some given molar concentration, by considering the following steps:
(i) NH3 (g) + xH2O (l) → NH4OH (aq) + (x-1)H2O (l)
(ii) HNO3 (l) + yH2O (l) → HNO3 (aq) + yH2O (l)
(iii) NH4OH (aq) + HNO3 (aq) → NH4NO3 (aq) + H2O (l)
or by considering the following (single) step:
(iv) NH4NO3 (s) + zH2O (l) → NH4NO3 (aq) + zH2O (l)
The enthalpy of neutralization (released at the scrubber), let us call it ΔHn, can be obtained as that corresponding to step (iii):
ΔHn = ΔHf[NH4NO3 (aq)] + ΔHf[H2O (l)] - ΔHf[NH4OH (aq)] - ΔHf[HNO3 (aq)]
Here, the last two contributing parcels can be derived from the enthalpy of aqueous dilution for NH3 and HNO3 (corresponding to steps i and ii), while considering also the enthalpies of formation of the relevant pure compounds. The first parcel can be derived from the enthalpy of aqueous dilution for NH4NO3, i.e., that corresponding to step (iv):
ΔHf[NH4NO3 (aq)] = ΔHs[NH4NO3] + ΔHf[NH4NO3(s)],
where ΔHs[NH4NO3] denotes the enthalpy of (aq.) solution that can be retrieved from the before mentioned reference.
By considering now steps (i) and (ii):
ΔHf[NH4OH (aq)] = ΔHs[NH4OH] + ΔHf[NH3 (g)] + ΔHf[H2O (l)]
ΔHf[[HNO3 (aq)] = ΔHs[[HNO3] + ΔHf[[HNO3 (l)],
where ΔHs[NH4OH] and ΔHs[HNO3] denote enthalpies of (aq.) solution.
Hence, the requested enthalpy (of neutralization) can be also given as:
ΔHn = ΔHs[NH4NO3] + ΔHf[NH4NO3(s)] - ΔHs[NH4OH] - ΔHf[NH3 (g)] - ΔHs[HNO3] - ΔHf[HNO3 (l)]
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