Calculate the standard molar entropy chnage for the following reactions at 298 K :
(a)`4Fe(s) + 3O_(2)(g) to 2Fe_(2)O_(3)(s)`
`[S^(@) (Fe_(2)O_(3)) = 87.4, S^(@)(Fe) = 27.3, S^(@)(O_(2)) = 205.1(all "in" JK^(-1)mol^(-1))`
(b) `Ca(s) + 2H_(2)O(l) to Ca(OH)_(2)(aq) + H_(2)(g)`
`[S^(@)Ca(OH)_(2) = -74.5, S^(@)(Ca) = 41.42, S^(@)(H_(2)) = 130.7, S^(@)(H_(2)O) = 69.91`(all in `JK^(-1) mol^(-1)`)
(c) `Na_(2)CO_(3)(s) + 2HCI (aq) to 2NaCI(aq) + H_(2)O(l) + CO_(2)(g)`
` = 115.13, S^(@)(H_(2)O) = 69.9, S^(@)(CO_(2)) = 213.74` (all in `JK^(-1)mol^(-1)`).

Answer

(a)`-549.4 J K^(-1) "mol"^(-1)`
(b) `-125.04 J K^(-1) "mol"^(-1)`
(c) `264.9 J K^(-1) "mol"^(-1)`