If a reaction is exergonic, what is the free energy change?
The correct answer and explanation is:
Correct Answer:
If a reaction is exergonic, the free energy change (ΔG) is negative.
Explanation (Approx. 300 words):
In thermodynamics, the free energy change (denoted as ΔG) is a measure of the energy available to do work during a chemical reaction. It is used to predict the direction and spontaneity of reactions.
An exergonic reaction is a chemical reaction that releases energy to the surroundings. These reactions occur spontaneously under the right conditions and are associated with a negative ΔG. This negative value indicates that the products of the reaction have lower free energy than the reactants, meaning energy is lost (usually as heat or work) during the transformation.
Mathematically, the Gibbs free energy equation is: ΔG=ΔH−TΔS\Delta G = \Delta H – T\Delta S
Where:
- ΔG = change in free energy
- ΔH = change in enthalpy (total energy)
- T = temperature (in Kelvin)
- ΔS = change in entropy (disorder)
In an exergonic process:
- ΔH is often negative (releases heat), or
- ΔS is positive (increase in disorder), or
- Both conditions are met, making ΔG negative.
An example of an exergonic reaction is cellular respiration, where glucose is broken down into carbon dioxide and water, releasing energy that the cell uses for work. The ΔG for this reaction is approximately -686 kcal/mol, indicating that the reaction releases a significant amount of energy.
In contrast, endergonic reactions have a positive ΔG and require an input of energy to proceed.
In summary, a negative ΔG characterizes an exergonic reaction. This means the reaction proceeds with a net release of free energy and can occur spontaneously, making it a key concept in understanding how energy flows in biological and chemical systems.