In which of the following reactions,standard reaction entropy change`(DeltaS^(@))`is positive and standard Gibb,s energy change`(DeltaG^(@))`decreases sharply with increasing temperature?

Options

A. C (graphite) `+(1)/(2)O_(2)(g) to CO(g)`
B. `CO(g) to (1)/(2)O_(2)(g) to CO_(2)(g)`
C. `Mg(s) to (1)/(2)O_(2)(g) to MgO(s)`
D. `(1)/(2) C ` (graphite) `+(1)/(2)O_(2)(g) to (1)/(2) CO_(2) (g)`

Answer

A

Explanation

Among the given reactions only in the case of
`C("graphite")+(1)/(2) (g) to CO(g)`
entropy increases because randomness (disorder) increases. Thus, standard entropy change (`DeltaS^(@))` is positive . Moreover, it is a combustion reaction and all the combustion reactions are generally exothermic , i.e., `DeltaH^(@)=ve`
We know that,
`DeltaG^(@)=DeltaH^(@)-TDeltaS^(@)`
`DeltaG^(@)a =-ve-T(+ve)`
Thus, as the temperature increases, the value of `DeltaG^(@)` decreases.