Question

Which of the following statements is correct according to the basic concept of thermodynamics which govern the feasibility of a metallurgical process?

• A. When the value of $△$G is positive for the equation $△$G=$△$H-T$△$S, the reaction will proceed.
• B. If reactants and products of two reactions are put together and net $△$G is -ve, the overall reaction will occur.
• C. On increasing the temperature, the value of $△$G becomes +ve.
• D. Feasibility of thermal oxidation of an ore can be established by Ellingham diagram in which a straight line shows the reduction reaction will proceed.

Answer 1

Answer: (B)

If reactants and products of two reactions are put together and net $△$G is -ve, the overall reaction will occur.

• The change in Gibbs energy, $\Delta G$ for any process at any specified temperature, is described by the equation:
  

$\Delta G=\Delta H-T\Delta S$

where $\Delta H$ is the enthalpy change and $\Delta S$ is the entropy change for the process.

• When the value of $\Delta G$ is negative in equation only then the reaction will proceed.$\Delta G$ can become negative in the following situations:

1. If $\Delta S$ is positive, on increasing the temperature (T), the value of

$T\Delta S$ increases so that $\Delta H$ < $T\Delta S$. In this situation, $\Delta G$ will become negative on increasing temperature.

2. If the coupling of the two reactions, i.e. reduction and oxidation, results in a negative value of $\Delta G$ for the overall reaction, the final reaction becomes feasible.

• Hence, option $B$ is the correct answer.