ANS:B - Gibbs free energy

During a phase change process such as sublimation, vaporization, melting, etc., the specific entropy does not change. Entropy (𝑆S) is a measure of the randomness or disorder of a system. During phase changes, the arrangement of particles changes (e.g., from solid to liquid or from liquid to gas), but the randomness or disorder of the particles remains the same. Therefore, the specific entropy of the substance does not change during these processes. The other properties mentioned—enthalpy, Gibbs free energy, and internal energy—can change during phase change processes depending on the conditions. Gibbs free energy, denoted as 𝐺G, is a fundamental concept in thermodynamics that plays a crucial role in determining whether a chemical or physical process will occur spontaneously under certain conditions. It's named after the American scientist Josiah Willard Gibbs, who formulated it. Gibbs free energy is defined as the energy available to do useful work in a system at constant temperature and pressure. It incorporates both the enthalpy (𝐻H) of the system and the entropy (𝑆S) of the system: 𝐺=𝐻−𝑇𝑆G=H−TS Where:

• 𝐺G is the Gibbs free energy.
• 𝐻H is the enthalpy of the system.
• 𝑇T is the temperature (in Kelvin).
• 𝑆S is the entropy of the system.

The Gibbs free energy tells us whether a process is spontaneous or non-spontaneous under constant temperature and pressure conditions. A process will be spontaneous if the Gibbs free energy change (Δ𝐺ΔG) is negative, meaning 𝐺final<𝐺initialGfinal​<Ginitial​. Conversely, if Δ𝐺ΔG is positive, the process will be non-spontaneous. If Δ𝐺ΔG is zero, the system is at equilibrium.

• If Δ𝐺<0ΔG<0, the process is spontaneous in the forward direction.
• If Δ𝐺>0ΔG>0, the process is non-spontaneous in the forward direction.
• If Δ𝐺=0ΔG=0, the system is at equilibrium.

Gibbs free energy is particularly useful in chemistry for predicting the direction of chemical reactions and phase transitions. It helps us understand whether a reaction will proceed towards the formation of products or if it will proceed in the reverse direction towards the formation of reactants. It also helps in determining the conditions under which reactions will occur spontaneously, such as whether they require an input of energy or release energy.