1. Nitric acid hydrates have been connected to heterogeneous reactions related t

Question

1. Nitric acid hydrates have been connected to heterogeneous reactions related to the formation of the ozone hole above Antarctica:

HNO3 nH2O(s) HNO3 (g) + nH2O (g)

where n=1, 2 and 3

Cl radicals react with ozone (O3) to form simple oxygen in the upper atmosphere – creating an ozone hole. HNO3 (g) reacts with Cl radicals and is therefore essential to keeping ozone levels high. Worsnop et al, in the journal Science (1993), compiled thermodynamic data for these reactions at 220K

For n=3, the values obtained for the Gibbs energy and the enthalpy are: G = 93 kJ/mol and delta H = 237 kJ/mol:

(ii) Assuming delta S and delta H are constant over the temperature range, estimate delta G at 180K

Explanation / Answer

G = 93 kJ/mol and dH = 237 kJ/mol

dG = dH -TdS

dS = - (dG - dH) / T

dS = - (93 - 237) / 220

dS = 0.6545

dG = dH - TdS

dG = 237 - (180 * 0.6545)

dG - 119.19 kJ/mol

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