Question

Which of the following statements is not correct about Ellingham diagram?

• A. $\Delta G$ increases with an increase in temprature
• B. It consists of plots of ${\Delta }_f{G}^{\circ }vsT$ for formation of oxide
• C. It express the kinetic of the reduction process
• D. None of the above

Answer 1

The correct option is C It express the kinetic of the reduction process

$\Delta G=\Delta H-T\Delta S$
Thus, negative value of $\Delta G$ increase with increase in temperature.
$\Rightarrow$ Ellingham diagram is a plot between ${\Delta }_f{G}^{\circ }$ and T for the formation of oxides of metals. A general reaction expressing oxidation is given by
$2xM\left(s\right)+O_2\left(g\right)\to 2MxO\left(s\right)$
$\Rightarrow$ Except for the process in which changes of phase takes place, each plot is a straight line. This temprature at which change of phase takes place is indicated by a positive increase in the slope.

$\Rightarrow$ The metal oxide is stable at the point in a curve blow which $\Delta G$ is negative.
Above this point, the metal oxide is unstable and decomposed on its own.

$\Rightarrow$ Feasibility of reductions of the upper line by the element represented by the lower line is determined by the difference in the two $\Delta rG$ values after the point of intersection in the Ellingham diagram. It does not tells about the kinetics of reduction process.