The key difference between Gibbs free energy and standard free energy is that the Gibbs free energy depends on the experimental conditions whereas the standard free energy describes the Gibbs free energy for reactants and products that are in their standard state.
The terms Gibbs free energy and standard free energy are common in physical chemistry. Both these terms give a nearly similar idea with a slight difference. The only difference between Gibbs free energy and standard free energy is in their experimental conditions such as temperature and pressure. Let us talk more details on these terms.
CONTENTS
1. Overview and Key Difference
2. What is Gibbs Free Energy
3. What is Standard Free Energy
4. Side by Side Comparison – Gibbs Free Energy vs Standard Free Energy in Tabular Form
5. Summary
What is Gibbs Free Energy?
Gibbs free energy is a thermodynamic quantity equal to the enthalpy (of a system or process) minus the product of the entropy and the absolute temperature. The symbol for this is “G”. it combines the enthalpy and entropy of a system into a single value. We can denote a change in this energy as “∆G”. This change can determine the direction of a chemical reaction at a constant temperature and a constant pressure.
Moreover, if the value of ∆G is positive, it is a non-spontaneous reaction while a negative ∆G indicates a spontaneous reaction. The term Gibbs free energy was developed by Josiah Willard Gibbs (1870). The equation for this quantity is as follows:
Figure 01: Equation for Gibbs free energy, where G is Gibbs free energy, H is enthalpy, T is absolute temperature, and S is entropy
What is Standard Free Energy?
Standard free energy is a thermodynamic quantity which gives the Gibbs free energy at standard experimental conditions. This means, in order to name the energy of a thermodynamic system as the standard free energy, the reactants and products of that system should be at standard conditions. Most of the times, following standard states, are applicable.
- Gases: 1 atm partial pressure
- Pure liquids: a liquid under the total pressure of 1 atm
- Solutes: an effective concentration of 1 M
- Solids: a pure solid under 1 atm pressure
Usually, the normal temperature for a thermodynamic system is 298.15 K (or 25◦C) for most of the practical purposes because we do the experiments at this temperature. But the accurate standard temperature is 273 K (0 ◦C).
What is the Difference Between Gibbs Free Energy and Standard Free Energy?
Gibbs free energy is a thermodynamic quantity equal to the enthalpy (of a system or process) minus the product of the entropy and the absolute temperature. More importantly, we calculate this quantity for the actual temperature and pressure of the experiment. Standard free energy is a thermodynamic quantity which gives the Gibbs free energy at standard experimental conditions. This is the key difference between Gibbs free energy and standard free energy. Though standard free energy is similar to the idea of Gibbs free energy, we calculate it only for the thermodynamic systems having reactants and products in their standard state.
Summary – Gibbs Free Energy vs Standard Free Energy
Both Gibbs free energy and standard free energy describes nearly similar idea in thermodynamics. The difference between Gibbs free energy and standard free energy is that the Gibbs free energy depends on the experimental conditions whereas the standard free energy describes the Gibbs free energy for reactants and products that are in their standard state.
Reference:
1. Libretexts. “Gibbs (Free) Energy.” Chemistry LibreTexts, Libretexts, 13 Jan. 2018. Available here
2. Mott, Vallerie. “Introduction to Chemistry.” Lumen, Open SUNY Textbooks. Available here
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