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In which of the following reactions, standard entropy change \left ( \Delta S^{o} \right ) is positive and standard Gibb's energy change \left ( \Delta G^{o} \right ) decreases sharply with increasing temperature?

  • Option 1)

    C\ graphite+\frac{1}{2}O_{2}\left ( g \right )\rightarrow CO\left ( g \right )

  • Option 2)

    CO\left ( g \right )+\frac{1}{2}O_{2}\left ( g \right )\rightarrow CO_2\left ( g \right )

  • Option 3)

    Mg\left (s \right )+\frac{1}{2}O_{2}\left ( g \right )\rightarrow MgO\left ( s \right )

  • Option 4)

    \frac{1}{2}C\ graphite+\frac{1}{2}O_{2}\left ( g \right )\rightarrow \frac{1}{2}CO_2\left ( g \right )

 

Answers (1)

 

Gibb's free energy (? G) -

\Delta G= \Delta H-T \Delta S
 

- wherein

\Delta G= Gibb's free energy

\Delta H= enthalpy of reaction

\Delta S= entropy

T= temperature

 

 C graphite + \frac{1}{2}O_{2}\left ( g \right )\rightarrow CO\left ( g \right )

\Delta ng=1-\frac{1}{2}=\frac{1}{2}

As amount of geseous substancance is increasing in product, thus \Delta S is positive for this reaction, and we know that \Delta G=\Delta H-T\Delta S. As \Delta S  is positive thus increase in tempreature will make T\Delta S more negative and \Delta G will decrease.


Option 1)

C\ graphite+\frac{1}{2}O_{2}\left ( g \right )\rightarrow CO\left ( g \right )

Correct Option

Option 2)

CO\left ( g \right )+\frac{1}{2}O_{2}\left ( g \right )\rightarrow CO_2\left ( g \right )

Incorrect Option

Option 3)

Mg\left (s \right )+\frac{1}{2}O_{2}\left ( g \right )\rightarrow MgO\left ( s \right )

Incorrect Option

Option 4)

\frac{1}{2}C\ graphite+\frac{1}{2}O_{2}\left ( g \right )\rightarrow \frac{1}{2}CO_2\left ( g \right )

Incorrect Option

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Vakul

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