Question

Which of the following conditions is necessary for a metallurgical reaction to be spontaneous at a given temperature?

• A. The reaction must have a negative entropy change.
• B. The enthalpy change must be negative.
• C. The Gibbs free energy change must be negative.
• D. The reaction must involve an increase in temperature.

Hint:

Always check the sign of \(\Delta G\) to determine spontaneity. A negative \(\Delta G\) indicates a reaction can occur without external input.

Answer 1

The Correct Option is C

For any chemical or metallurgical reaction to be spontaneous at a given temperature, the primary thermodynamic condition is that the change in Gibbs free energy \((\Delta G)\) must be negative.
The Gibbs free energy is given by the equation: \[ \Delta G = \Delta H - T\Delta S \] Where:
\(\Delta H\) = change in enthalpy
\(\Delta S\) = change in entropy
\(T\) = absolute temperature in Kelvin
Even if \(\Delta H\) is positive or \(\Delta S\) is negative, a reaction may still be spontaneous depending on temperature. But the decisive factor remains: \[ \Delta G<0 \] Therefore, the spontaneity of a metallurgical reaction is governed by the sign of \(\Delta G\), and it must be negative.