Spontaneous change criterion for

An isolated system is one that exchanges neither matter nor energy with the surroundings. What is the entropy criterion for spontaneous change in an isolated system Give an example of a spontaneous process in an isolated system. 

Thermodynamics is used to predict whether reactants have a spontaneous tendency to change into products. This tendency is associated with a decrease in the free energy or Gibbs energy of the system (G) to a minimum. As a consequence, the thermodynamic criterion for spontaneous change at constant temperature and pressure is AG < 0. Under standard conditions (concentrations = 1 M, and P = 1 atm), the standard Gibbs energy variation (AG°) is related with the equilibrium constant (A) by equation 11 ... 

The entropy provides a criterion of spontaneous change and equilibrium at constant U and V because (dS) y 0. Thus the entropy of an isolated system can only increase and has its maximum value at equilibrium. The internal energy also provides a criterion for spontaneous change and equilibrium. That criterion is (dl/)s>K < 0, which indicates that when spontaneous changes occur in a system described by equation 2.2-1 at constant S and V, U can only decrease and has its minimum value at equilibrium. 

The use of a Legendre transform has introduced an intensive property P as an independent variable. It can be shown that the criterion for spontaneous change and equilibrium is given by (dH)S P 0. 

The use of this Legendre transform has introduced the intensive property T as an independent variable. It can be shown that the criterion for spontaneous change and equilibrium is given by (dG)rp 0. The Gibbs energy is so useful because T and P are convenient intensive variables to hold constant and because, as we will see shortly, if G can be determined as a function of T and P, then S, V, H, and U can all be calculated. 

For a system of chemical reactions, the criterion for spontaneous change and equilibrium is dG 0 at T, P, nci. When the pH is specified, the criterion for spontaneous change and equilibrium becomes dG 0 at T, P, n ci, pH, where ri represents the set of amounts of components other than hydrogen. 

It is important to be able to write the fundamental equation for a system of chemical reactions in terms of components because components are involved in the criterion for spontaneous change and equilibrium. We have seen earlier (Section 2.3) that this is done by eliminating one chemical potential from the fundamental equation with each independent equilibrium condition of the form v /q = 0 to obtain... 

The Legendre transform that defines the further transformed Gibbs energy G", which provides the criterion for spontaneous change and equilibrium in dilute... 

Criterion for spontaneous change and equilibrium at constant independent... 

Since there are Ns + 2 intensive variables and two relations between them, F = Ns. This is in agreement with D = F + p. The criterion for spontaneous change and equilibrium for this system is dG 0 at constant T, P, and nci. ... 

Since coenzymes, and perhaps other reactants, are in steady states in living cells, it is of interest to use a Legendre transform to define a further transformed Gibbs energy G" that provides the criterion for spontaneous change and equilibrium at a specified pH and specified concentrations of coenzymes. This process brings in a further transformed entropy S" and a further transformed enthalpy H", but the relations between these properties have the familiar form. 

The transformed Gibbs energy provides the criterion for spontaneous change and equilibrium in systems of enzyme-catalyzed reactions when the independent variables for the system are T, P, pH, and Wc - Notice that making this Legendre transform has introduced ) as a natural variable, but it has not changed the number of natural variables because there is now one less component that is conserved, the hydrogen atom component. 

When the pH and [O2] are specified, the criterion for spontaneous change and equilibrium is provided by G ", and the reaction system 4.2-1 is represented by a single reactant Hav M02av, that is the pseudoisomer group Hav M and Hav MO2. The fundamental equation for the further transformed Gibbs energy is given by... 

Processes An Introduction— A process that proceeds without external intervention is said to be a spontaneous process. A nonspontaneous process cannot occur without external intervention. If a process is spontaneous in one direction, then it is nonspontaneous in the reverse direction. Some spontaneous processes are exothermic, and others are endothermic, so the criterion for spontaneous change cannot be based on enthalpy changes alone. The direction of spontaneous change involves changes in another property called entropy. Entropy provides a measure of the number of ways a given quantity of energy can be dispersed, or distributed, among the particles of the system. 

Clausius s Ideas Absolute Entropies 13-4 Criterion for Spontaneous Change The Second Law of Thermodynamics... 

We will soon see that the criterion for spontaneous change can be expressed in terms of a thermodynamic quantity called entropy. Let s first focus our attention on developing a conceptual model for understanding entropy. Then, we will be able to use entropy, more specifically entropy changes, to explain why certain processes are spontaneous and others are not. 

We could use expression (13.10) as the basic criterion for spontaneous change, but it would be preferable to have a criterion that could be applied to the system itself, without having to worry about changes in the surroundings. Such a criterion can be developed in a straightforward manner for processes such as phase changes and chemical reactions that occur at constant temperature and constant pressure. 

The right side of this equation has terms involving only the system. On the left side appears the term ASuniv/ which embodies the criterion for spontaneous change, that for a spontaneous process, ASuuiv > 0. 

Now, by noting that AG is negative when ASuniv is positive, we have our final criterion for spontaneous change based on properties of only the system itself. 

Our main criterion for spontaneous change is that Aj-G < 0. According to equation (19.14), however, redox reactions have the property that, if Afi < 0, then Eceii > 0. That is, E<.eii must be positive if Afi is to be negative. Predicting the direction of spontaneous change in a redox reaction is a relatively simple matter by using the following ideas ... 

EXAMPLE 19-6 Applying the Criterion for Spontaneous Change in a Redox Reaction... 

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