Spontaneous processes energy

Thus, for spontaneous processes at constant temperature and volume a new quantity, the Helmholtz free energy A, decreases. At equilibrium under such restrictions cL4 = 0. 

For spontaneous processes at constant temperature and pressure it is the Gibbs free energy G that decreases, while at equilibrium under such conditions dG = 0. 

The more negative the value of AG, the more energy or useful work can be obtained from the reaction. Reversible processes yield the maximum output. In irreversible processes, a portion of the useful work or energy is used to help carry out the reaction. The cell voltage or emf also has a sign and direction. Spontaneous processes have a positive emf the reaction, written in a reversible fashion, goes in the forward direction. 

Thus the formation of an ideal solution from its components is always a spontaneous process. Real solutions are described in terms of the difference in the molar Gibbs free energy of their formation and that of the corresponding ideal solution, thus ... 

The oxidation of hydrogen to water (Hj -t- i Oj -> HjO) is thermodynamically spontaneous and the energy released as a result of the chemical reaction appears as heat energy, but the decomposition of water into its elements is a non-spontaneous process and can be achieved only by supplying energy from an external source, e.g. a source of e.m.f. that decomposes the water electrolytically. Furthermore, although the heat produced by the spontaneous reaction could be converted into electrical energy, the electrical... 

Key Terms enthalpy, H free energy of formation, AG standard entropy change, AS° entropy, S spontaneous process standard free energy change, AG° free energy, G... 

The change in Gibbs free energy for a process is a measure of the change in the total entropy of a system and its surroundings at constant temperature and pressure. Spontaneous processes at constant temperature and pressure are accompanied by a decrease in Gibbs free energy. 

Spontaneous processes result in the dispersal of matter and energy, hi many cases, however, the spontaneous direction of a process may not be obvious. Can we use energy changes to predict spontaneity To answer that question, consider two everyday events, the melting of ice at room temperature and the formation of ice in a freezer. 

Schematic view of the spontaneous process for a water-and-ice mixture on a table. The energy-absorbing process, melting, is spontaneous under these conditions.

C14-0066. Each of the following statements is false. Rewrite each so that it makes a correct statement about free energy (a) A Gtotal fo " spontaneous process, (b) A Gsystem increases in any process at constant T and P. (c) A U = AG- T AS. 

The open cell discussed was considered as an equilibrium cell since equilibrium was established across each individual interface. However, the cell as a whole is not in equilibrium the overall Gibbs energy of the full reaction is not zero, and when the circuit is closed, an electric current flows that is attended by chemical changes (i.e., a spontaneous process sets in). 

In thermodynamics, entropy enjoys the status as an infallible criterion of spontaneity. The concept of entropy could be used to determine whether or not a given process would take place spontaneously. It has been found that in a natural or spontaneous process there would be an increase in the entropy of the system. This is the most general criterion of spontaneity that thermodynamics offers however, to use this concept one must consider the entropy change in a process under the condition of constant volume and internal energy. Though infallible, entropy is thus not a very convenient criterion. There have, therefore, been attempts to find more suitable thermodynamic functions that would be of greater practical... 

An important use of the free energy function is to obtain a simple criterion for the occurrence of spontaneous processes and for thermodynamic equilibrium. According to the second law of thermodynamics,... 

Notice that dephasing of the transverse magnetization does not affect Mz a T2 process involves no energy transfer but, being a spontaneous process, does involve an increase in the entropy of the spin system. 

AG, AH, and AS are positive quantities for increases in the corresponding property, negative for decreases. There is a natural tendency for the free energy of the system to decrease, so that AG is negative for a spontaneous process. 

The spontaneous process that occurs when the stretched rubber band is allowed to return to its original, random arrangement of polymer molecules, must be driven by the increase in the mass and energy dispersal of the system, since the reaction is endothermic (AH > 0). 

The Helmholtz and Gibbs energies on the other hand involve constant temperature and volume and constant temperature and pressure, respectively. Most experiments are done at constant Tandp, and most simulations at constant Tand V. Thus, we have now defined two functions of great practical use. In a spontaneous process at constant p and T or constant p and V, the Gibbs or Helmholtz energies, respectively, of the system decrease. These are, however, only other measures of the second law and imply that the total entropy of the system and the surroundings increases. 

We now introduce the second law of thermodynamics a physicochemical process only occurs spontaneously if accompanied by an increase in the entropy S. By corollary, a non-spontaneous process - one that we can force to occur by externally adding energy - would proceed concurrently with a decrease in the energetic disorder. 

Any further reaction beyond (eq) would not only fail to liberate any further energy, but also would in fact consume energy (we would start to go uphill on the right-hand side of the figure). Any further increment of reaction would be characterized by AG > 0, implying a non-spontaneous process, which is why the reaction... 

The first law of thermodynamics states that the total energy of the universe is constant. The second law of thermodynamics states, that in all spontaneous processes, the entropy of the system increases. Entropy is a measure of the dispersion of energy from a localized one to a more disperse one. It can be... 

The Gibbs free energy for a spontaneous process has a sign. 

---