Spontaneous reactions Gibbs free energy

It is the Gibbs free energy change which determines whether a reaction proceeds (spontaneous) or not (non-spontaneous). The Gibbs free energy change, AG , and the equilibrium constant, K, are related by the following expression ... 

If a corrosion reaction is to be spontaneous, the Gibbs free energy associated with the cell reaction must be negative JGcell<9. These free-energy changes may be related to the relevant equilibrium potentials ... 

Chemical systems spontaneously react in a fashion that lowers their overall free energy. At a constant temperature and pressure, typical of many bench-top chemical reactions, the free energy of a chemical reaction is given by the Gibb s free energy function... 

An isothermal reaction can proceed spontaneously only if the total Gibbs free energy of the system decreases, i.e. the free energy of the reactants must be greater than the free energy of the products. For a reaction... 

The decrease in Gibbs free energy as a signpost of spontaneous change and AG = 0 as a criterion of equilibrium are applicable to any kind of process, provided that it is occurring at constant temperature and pressure. Because chemical reactions are our principal interest in chemistry, we now concentrate on them and look for a way to calculate AG for a reaction. 

The thermodynamic function used as the criterion of spontaneity for a chemical reaction is the Gibbs free energy of reaction, AG (which is commonly referred to as the reaction free energy ). This quantity is defined as the difference in molar Gibbs free energies, Gm, of the products and the reactants ... 

Use the standard Gibbs free energies of formation in Appendix 2A to calculate AG° for each of the following reactions at 25°C. Comment on the spontaneity of each reaction under standard conditions at 25°C. 

STRATEGY Calculate the reaction quotient and substitute it and the standard Gibbs free energy of reaction into Eq. 5. If AGr < 0, the forward reaction is spontaneous at the given composition. If AGr > 0, the reverse reaction is spontaneous at the given composition. If AGr = 0, there is no tendency to react in either direction the reaction is at equilibrium. At 298.15 K, RT = 2.479 kJ-moF h... 

Because the Gibbs free energy of reaction is negative, the formation of products is spontaneous (as indicated by the green region in the diagram) at this composition and temperature. 

Because 1 C-V = l J, we can conclude that the Gibbs free energy of reaction A under these conditions is —201 kj because this value is negative, the reaction is spontaneous in the forward direction for this composition of the cell. 

Redox reactions that have a positive Gibbs free energy of reaction are not spontaneous, but an electric current can be used to make them take place. For example, there is no common spontaneous chemical reaction in which fluorine is a product, and so the element cannot be isolated by any common chemical reaction. It was not until 1886 that the French chemist Henri Moissan found a way to force the... 

Now, let s return to the Gibbs free energy equation to determine if hydrogen will react spontaneously with oxygen to form water. The equation for the reaction may be written as... 

Spontaneous reaction A reaction where the Gibbs free energy is negative. Such reactions proceed naturally without requiring added energy after initiation. 

Which of the following is NOT a variable in the Gibbs free energy equation, which determines reaction spontaneity ... 

Whether a reaction is spontaneous or not depends on thermodynamics. The cocktail of chemicals and the variety of chemical reactions possible depend on the local environmental conditions temperature, pressure, phase, composition and electrochemical potential. A unified description of all of these conditions of state is provided by thermodynamics and a property called the Gibbs free energy, G. Allowing for the influx of chemicals into the reaction system defines an open system with a change in the internal energy dt/ given by ... 

The condition for a spontaneous reaction is that the change in the Gibbs free energy must be negative (dG < 0) - a so-called exoergic reaction. 

Plan Evaluate A7/KI1 and AS. To assess the temperature range over which the reaction is spontaneous, use the signs of AH and AS and the Gibbs free energy change equation, AG = AH - TAS. Assume that AH and AS are independent of temperature. 

Our goal in this chapter is to help you learn the laws of thermodynamics, especially the concepts of entropy and free energy. It might be helpful to review Chapter 6 on thermochemistry and the writing of thermochemical equations. The concept of Gibbs free energy (G) will be useful in predicting whether or not a reaction will occur spontaneously. Just like in all the previous chapters, in order to do well you must Practice, Practice, Practice. 

One of the goals of chemists is to be able to predict if a reaction will be spontaneous. A reaction may be spontaneous if its AH is negative or if its AS is positive, but neither one is a reliable predictor by itself about whether or not a reaction will be spontaneous. Temperature also plays a part. A thermodynamic factor that takes into account the entropy, enthalpy, and temperature of the reaction would be the best indicator of spontaneity. This factor is the Gibbs free energy. 

Whereas a thermal reaction from R to P2 or P3 involves an increase in Gibbs free energy and so will not occur spontaneously, the photochemical reactions from R involve a decrease in free energy and so are more likely to occur spontaneously. This allows the photochemical production of so-called energy-rich or strained compounds such as P2 and P3 to be carried out at low temperatures, as these products may undergo decomposition at higher temperatures. 

The Gibbs free energy is a thermodynamic quantity that relates the enthalpy and entropy, and is the best indicator for whether or not a reaction is spontaneous. 

The Gibbs free energy is the best single thermodynamic indicator of whether a reaction will be spontaneous (review the Thermodynamics chapter). The Gibbs free energy for a reaction can be calculated from the E° of the reaction using the following equation ... 

Gibbs free energy The Gibbs free energy (G) is a thermodynamic function that combines the enthalpy, entropy, and temperature. AG is the best indicator of whether or not a reaction will be spontaneous. 

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