Question

Predict the sign change of $\text{ }\\!\\!\Delta\\!\\!\text{ G}$ for a reaction that is exothermic and accompanied by an increase in entropy.

Answer 1

Hint: In thermodynamics, entropy is the measure of a system's thermal energy per unit temperature that is unavailable for doing useful work. Exothermic means when the reaction is accompanied by the release of heat.

Complete step by step solution:
Entropy is the measure of the molecular disorder, or randomness, of a system. Every reaction has an energy associated with it. This energy change can be written as: $\text{ }\\!\\!\Delta\\!\\!\text{ G = }\\!\\!\Delta\\!\\!\text{ H - T }\\!\\!\Delta\\!\\!\text{ S}$, $\text{ }\\!\\!\Delta\\!\\!\text{ H}$ represents enthalpy change, $\text{ }\\!\\!\Delta\\!\\!\text{ G}$ represents free energy change and $\text{ }\\!\\!\Delta\\!\\!\text{ S}$ represents entropy change. We are given that the reaction is exothermic therefore, the sign of $\text{ }\\!\\!\Delta\\!\\!\text{ H}$ will be negative. It is given that entropy increases, so the sign of $\text{ }\\!\\!\Delta\\!\\!\text{ S}$ will be positive.
So, the overall value of $\text{ }\\!\\!\Delta\\!\\!\text{ G}$ will be negative.
From the above we can say that the sign change of $\text{ }\\!\\!\Delta\\!\\!\text{ G}$ for a reaction that is exothermic and accompanied by an increase in entropy is negative.
Additional Information:
The free energy change $\text{ }\\!\\!\Delta\\!\\!\text{ G}$ associated with a reaction tells whether or not the reaction will occur under the specified conditions.
The entropy change associated with a reaction measures how the reaction affects the orderliness of the system.
A reaction that is spontaneous is always accompanied by the net release of free energy.

Note: When a system is more disordered it means it has more disorder in the way the energy is arranged. A system is stable when it's entropy is at its maximum. Every system wants to attain stability so a system becomes more stable when its energy is spread out in a more disordered state.