Spontaneity of reactions Knowledge-Based Download PDF

Questions

1. 1.

   Which statement correctly describes a chemical reaction that is classified as thermodynamically spontaneous?

   • A) It has a natural tendency to proceed in the forward direction without requiring continuous external intervention.
   • B) It proceeds at a rapid, easily observable rate under the given conditions.
   • C) It must be an exothermic process that releases thermal energy to the surroundings.
   • D) It proceeds forward until all reactant molecules are completely consumed.
2. 2.

   At constant temperature and pressure, which quantity must be strictly negative for a chemical reaction mixture to proceed spontaneously in the forward direction?

   • A) The instantaneous Gibbs free energy change ($\Delta G$)
   • B) The standard Gibbs free energy change ($\Delta G^\circ$)
   • C) The enthalpy change of the reaction ($\Delta H$)
   • D) The standard enthalpy change of formation ($\Delta H_\text{f}^\circ$)
3. 3.

   According to the Second Law of Thermodynamics, which of the following criteria is both necessary and sufficient for any process to be thermodynamically spontaneous?

   • A) $\Delta S_{\text{system}} > 0$
   • B) $\Delta H_{\text{system}} < 0$
   • C) $\Delta S_{\text{universe}} > 0$
   • D) $\Delta G_{\text{system}} > 0$
4. 4.

   For an endothermic chemical reaction that results in an increase in system entropy ($\Delta H > 0$ and $\Delta S > 0$), under what condition is the reaction thermodynamically spontaneous at constant temperature and pressure?

   • A) At sufficiently high temperatures such that $T\Delta S > \Delta H$
   • B) At sufficiently low temperatures such that $T\Delta S < \Delta H$
   • C) At all temperatures because $\Delta S > 0$ always guarantees spontaneity
   • D) At no temperature because endothermic reactions cannot occur spontaneously
5. 5.

   Under which combination of enthalpy change ($\Delta H$) and entropy change ($\Delta S$) is a chemical process thermodynamically spontaneous at all temperatures?

   • A) $\Delta H < 0$ and $\Delta S > 0$
   • B) $\Delta H > 0$ and $\Delta S < 0$
   • C) $\Delta H < 0$ and $\Delta S < 0$
   • D) $\Delta H > 0$ and $\Delta S > 0$