Question

The free change for a reversible reaction at equilibrium is:
A. Zero
B. Positive
C. Negative
D. None of these

Answer 1

Hint: The Gibbs free energy for a reversible reaction depends on the factors like enthalpy, entropy and temperature and it makes the reaction spontaneous, when it is negative.

Complete step by step solution:
Gibbs free energy is defined as “that thermodynamic quantity of a system the decrease in whose value during a process is equal to the maximum possible useful work that can be obtained from the system”.
Basically, Gibbs free energy is a measure of the amount of energy available to do work in an isothermal (at constant temperature) and isobaric (at constant pressure) thermodynamic system.
The term ‘free’ in Gibbs free energy refers to the amount of energy present in a system in usable form.
For a change taking place at constant temperature and pressure:
$\Delta G = \Delta H - T\Delta S$ ,where $\Delta G$ is change in Gibbs free energy, $\Delta H$ is change in enthalpy of reaction, $\Delta S$ is change in entropy and $T$ is the constant temperature at which reaction takes place.
We should know the criteria in terms of Gibbs free energy for spontaneity of the process which are as follows:
If $\Delta G$ is negative, then the process will be spontaneous.
If $\Delta G$ is positive, then the direct process is non-spontaneous.
If $\Delta G$ is zero, then we can say that the given process is in equilibrium.
Therefore, from above points, we can now say that option A is the correct answer.

Note: It should be remembered that the Gibbs free energy of a system is state function i.e. Does not depend on path and depends only on the initial and final state of thermodynamic properties.