Nitrogen dioxide, `NO_(2)` an air pollutant, dissolves in rain-water to form a dilute solution of nitric acid. The equation for the reaction is: `3NO _(2) (g) + H_(2) O(l) to 2HNO _(3) (1) + NO (g)`
Calculate `Delta S ^(@)` for the reaction in `JK^(-1).` The standard entropy of `HNO _(3) (l) , NO (g), NO _(2) (g ) and H _(2)O (l)` are 155.6,210.6,240.5 and 69.96 J `mol^(-1) K^(-1)` respectively.

Options

A. `155. 6 J K ^(-1)`
B. `-155.6 J K ^(-1)`
C. `269. 7 JK ^(-1)`
D. `-269.7 JK ^(-1)`

Answer

D

Explanation

The entropy chane is given by `Delta S ^(@) = sumS ^(@)` (products) `- sum S ^(@)` (reactants)
`= [ 2 S ^(@) (HNO _(3) (l)) + S ^(@) (NO (g)) ]-[ 3 S ^(@) (NO _(2) (g)) + S ^(@) (H _(2) O (l))]`
Subsituting values, we get `Delta S ^(@) [2 mol xx (155.6 J mol ^(-1) K ^(-1)) +1 mol xx (210.6 J mol ^(-1) K ^(-1))]`
`- [ 3 ol xx (240 . 5 J mol ^(-1) K ^(-1) ) + 1 mol xx (69.96 J mol ^(-1) K ^(-1)) ],` Solving we get `Delts S ^(@) =- 269 . 7 JK ^(-1)`