Defining Gibbs Free Energy
Gibbs free energy, denoted as G, is a thermodynamic quantity that represents the maximum amount of non-expansion work that can be extracted from a system at constant temperature and pressure. In chemistry, we are usually interested in the change in Gibbs free energy (ΔG), which indicates the spontaneity of a chemical reaction.
Section 2: The Gibbs Free Energy Equation
The change in Gibbs free energy is calculated using the fundamental equation: ΔG = ΔH - TΔS. In this formula, ΔH is the change in enthalpy (the total heat of the system), T is the absolute temperature in Kelvin, and ΔS is the change in entropy (the measure of disorder or randomness in the system).
Section 3: Interpreting the Sign of ΔG
The sign of the calculated ΔG value is crucial for predicting a reaction's direction. If ΔG is negative (ΔG < 0), the reaction is spontaneous and will proceed in the forward direction. If ΔG is positive (ΔG > 0), the reaction is non-spontaneous and requires energy input to occur. If ΔG is zero (ΔG = 0), the system is at equilibrium, with no net change.
Section 4: Why Is Gibbs Free Energy Important?
Gibbs free energy is a cornerstone of chemical thermodynamics because it combines enthalpy and entropy into a single value to predict reaction feasibility. It is essential in fields like materials science, biochemistry, and chemical engineering for determining reaction conditions, calculating equilibrium constants, and understanding energy transformations in biological systems, such as ATP hydrolysis.