6A.4t Nitric acid hydrates have received much attention as possible catalysts fo
ID: 549454 • Letter: 6
Question
6A.4t Nitric acid hydrates have received much attention as possible catalysts for heterogeneous reactions that bring about the Antarctic ozone hole. Standard reaction Gibbs energies are as follows: 0H20(g) H2O(s) 4Ge-23.6 kJ/mol (ii) H2O(g) + HNO3(g) HNOg. H2O(s) ,G -57.2 kJ/mol (iii) 2 H2O(g) + HNO3(g) HNOg2H2O(s) -G-85.6 kJ/mol (iv) 3 H20(g) + HNO3(g) HNOg-3H2O(s) )-1 12.8 kJ/mol which solid is thermodynamically most stable at 190 K If pH2-0.13 bar and pH NO3-0.41 nbar Hint: Try computing 4G for each reaction under the prevailing conditions; if more than one solid form spontaneously, examine .g for the conversion of one solid to another.Explanation / Answer
Nitric acid hydrates have received much attention as possible catalysts for heterogeneous reactions that bring about the Antarctic ozone hole. Worsnop et al. investigated the thermodynamic stability of these hydrates under conditions typical of the polar winter stratosphere. Standard reaction Gibbs energies can be computed for the following reactions at 190 K from their data:
(i) H2O (g)H2O (s) rG7= 23.6 kJ mol1
(ii) H2O (g) + HNO3 (g)HNO3·H2O (s) rG = 57.2 kJ mol1
(iii) 2 H2O (g) + HNO3 (g)HNO3·2H2O (s) rG = 85.6 kJ mol1
(iv) 3 H2O (g) + HNO3 (g)HNO3·3H2O (s) rG = 112.8 kJ mol1
Which solid is thermodynamically most stable at 190 K if pH2O = 1.3×107 bar and pHNO3 = 4.1×1010bar?
Delta G190 =( Delta G220 x ( T 190 / T220 ) + (DELTA H + (1 -190 k/220k)
For Monohydrate
Delta G190 =(46.2 kj /mol) x (190 k/220k ) + (127 kj /mol) + (1 -190 k/220k)
Delta G190 = 57.2 kj /mol
For dihydrate
Delta G190 =(69.4 kj /mol) x (190 k/220k ) + (188 kj /mol) + (1 -190 k/220k)
Delta G190 = 85.6 kj /mol
For trhydrate
Delta G190 =(93.2 kj /mol) x (190 k/220k ) + (273 kj /mol) + (1 -190 k/220k)
Delta G190 = 112.8 kj /mol
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