The concept was developed by the German scientist Hermann von Helmholtz. This term can be given in the below equation. Therefore, when a chemical reaction in a system is considered, the change in the energy that is at constant temperature and volume should be a negative value in order for it to be a spontaneous reaction. Gibbs Free Energy: Gibbs free energy can be defined as the maximum reversible work that can be obtained from a particular system. Gibbs Free Energy: The Gibbs free energy is calculated for systems under constant temperature and pressure.
Helmholtz Free Energy: The Helmholtz free energy is calculated for systems under constant temperature and volume. Gibbs Free Energy: The Gibbs free energy is often used since it considers a constant pressure condition. Helmholtz Free Energy: The Helmholtz free energy is not much used because it considers a constant volume condition.
Gibbs Free Energy: Chemical reactions are spontaneous when the Gibbs free energy change is negative. Helmholtz Free Energy: Chemical reactions are spontaneous when the Helmholtz free energy change is negative. Gibbs free energy and Helmholtz free energy are two thermodynamic terms used in describing the behavior of a system thermodynamically.
Both these terms include the internal energy of the system. The main difference between Gibbs and Helmholtz free energy is that Gibbs free energy is defined under constant pressure, while Helmholtz free energy is defined under constant volume. The direction of change is determined by the distribution of energy. In spontaneous change, things tend to a state in which the energy is more chaotically dispersed. A change is spontaneous, if it leads to greater randomness and chaos in the universe as a whole.
The degree of chaos, randomness, or dispersal of energy is measured by a state function called the entropy. In fact, the amount of extra disorder caused by a given amount of heat q depends on the temperature. To analyze the direction of change, we have to consider changes in both system and the surrounding. The following Clausius inequality shows what happens when heat energy is transferred between the system and the surrounding. First, a modeling of the Gibbs Energy by way of equation:.
All of the members on the right side of this equation are state functions , so G is a state function as well. The change in G is simply:. We will start with an equation for the total entropy change of the universe. Our goal is to whittle it down to a practical form, like a caveman shaping a unwieldy block of stone into a useful hand held tool! An equation with variables of such scope is difficult to work with.
We want to do away with the vagueness, and rewrite a more focused equation. We'll consider the case where temperature and pressure is constant. Here we go:. As a quick note, let it be said that the name "free energy", other than being confused with another energy exactly termed, is also somewhat of a misnomer. The multiple meanings of the word "free" can make it seem as if energy can be transferred at no cost; in fact, the word "free" was used to refer to what cost the system was free to pay, in the form of turning energy into work.
The Gibbs Energy reaches the minimum value when equilibrium is reached. Here, it is represented as a graph, where x represents the extent of how far the reaction has occurred. The definition is self evident from the equation.
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