What characterizes a spontaneous reaction?

• A. A positive change in free energy
• B. A negative change in free energy
• C. The absence of catalysts
• D. An increase in entropy

Answer: (B)

A spontaneous reaction is characterized by a negative change in free energy, meaning that the process can occur without the input of additional energy. In thermodynamics, the Gibbs free energy change (( \Delta G )) determines whether a reaction will proceed spontaneously. If ( \Delta G ) is less than zero, the reaction is spontaneous, indicating that the products have lower free energy than the reactants, which is favorable for the reaction to occur.

In spontaneous reactions, the natural tendency is for systems to move toward a state of lower free energy and higher stability. A negative ( \Delta G ) also correlates with an increase in the entropy of the universe, in accordance with the second law of thermodynamics. While factors like the presence of catalysts can affect the activation energy and the rate of a reaction, they do not alter the spontaneity; thus, a reaction can be spontaneous regardless of catalytic presence as long as the free energy change remains negative.

Overall, a negative change in free energy is critical for identifying spontaneity in reactions, as it reflects the thermodynamic favorability of the process.