Gibbs Free Energy Equation
The Gibbs free energy equation is one of the most famous equations in physics. It was first formulated by James Clerk Maxwell in 1879.
In the following, we will analyze the Gibbs free energy equation.
It describes how much work an object does when it changes its kinetic energy (KE) into potential energy (PE).
A major part of our life is the energy that we gain from food. Actually, food is a source of potential and kinetic energy. The potential energy of food comes from the bonds that hold them together.
When you eat food, your body breaks these bonds and releases the potential energy. Your body also gains kinetic energy, which it loses as heat.
It is common knowledge that the human body is an open system which means that it is not a closed system. It absorbs energy from food, and gives out waste and heat. The latter two are lost as the body is not a perfect system, hence it is impossible to gain 100% energy.
Let’s consider a closed container with air, a balloon, and a rubber band. When you let go of the rubber band, it shoots upward. When you shoot a rubber band into the air, it transfers its KE to the air molecules.
The same happens when you let go of a balloon. The balloon is held down by the force of gravity. When you let go of it, it transfers its PE to the earth’s surface. The rubber band and the balloon do not bounce back to you when they hit the ground. The potential energy that they gain, changes into heat through the air.
When the rubber band and the balloon are at rest, they have no kinetic energy. If they were at rest, they would not give off heat. So, no change in heat is accounted for when the rubber band and the balloon are at rest.
This makes sense because the object does not move, and hence there is no transfer of kinetic energy.
Gibbs free energy equation shows the relationship of the change in heat and the change in potential energy when a system goes from one state to another. The equation reads,
Gibbs free energy (G), is the maximum useful doing work that can be done.
Kinetic energy (K) is the energy of the system due to its motion.
Gibbs free energy is a term used in physical chemistry and chemical engineering. It is the maximum useful energy that can be extracted from a thermodynamic system when it changes from one state to another.
In chemical engineering, Gibbs energy is used to measure the feasibility of a reaction. The change in free energy (ΔG) gives an indication of whether a chemical reaction will be spontaneous or not. In other words, it gives an indication of whether or not one substance will be able to transform into another.
The larger the negative value of the free energy drop (ΔG) during a reaction, the more likely the reaction will occur. The smaller the positive value of the drop (ΔG), the less likely the reaction will occur.
At equilibrium, ΔG equals zero. The value of ΔG is calculated by subtracting the free energy of the products from the free energy of the reactants.
Sources & references used in this article:
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- Thermodynamics of methanogenic intermediary metabolism in littoral sediment of Lake Constance (F Rothfuss, R Conrad – FEMS Microbiology Ecology, 1993 – academic.oup.com)
- Anaerobic microbial metabolism can proceed close to thermodynamic limits (BE Jackson, MJ McInerney – Nature, 2002 – nature.com)
- Thermodynamics of hydrogen metabolism in methanogenic cocultures degrading ethanol or lactate (HJ Seitz, B Schink, R Conrad – FEMS Microbiology Letters, 1988 – academic.oup.com)