Which statement best describes the difference between an exothermic reaction and an exergonic reaction?

• A. Both exothermic and exergonic reactions absorb energy from their surroundings.
• B. An exothermic reaction absorbs heat, while an exergonic reaction absorbs free energy.
• C. An exothermic reaction releases heat, while an exergonic reaction releases free energy.
• D. Exothermic reactions occur only in open systems, while exergonic reactions occur only in closed systems.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the definitions of exothermic and exergonic reactions. An exothermic reaction is one that releases heat energy to its surroundings, meaning the enthalpy change (\( \Delta H \)) is negative.
2. Step 2: Recognize that an exergonic reaction is defined by the release of free energy, specifically Gibbs free energy (\( \Delta G \)), which must be negative for the reaction to be spontaneous.
3. Step 3: Note the difference between heat and free energy: heat (enthalpy) is a form of energy transfer related to temperature change, while free energy includes both enthalpy and entropy changes and determines spontaneity.
4. Step 4: Compare the statements given in the problem to these definitions. The correct description should state that exothermic reactions release heat, and exergonic reactions release free energy.
5. Step 5: Conclude that the best statement is: 'An exothermic reaction releases heat, while an exergonic reaction releases free energy,' because it accurately reflects the thermodynamic concepts involved.