Isothermal system, spontaneous processes

In thermodynamics (see e.g. [1]) it is shown that for any isolated (closed) system (which does not exchange energy with its surroundings), spontaneous transformations take place with an increase in the entropy AS of the system. For a non-isolated system in isothermal conditions, spontaneous processes take place with a negative variation of free enthalpy AG where... 

The concept of a spontaneous reaction may be a misnomer in general, although a spontaneous process is a more appropriate concept. For (say) a kinetically feasible (closed system) isothermal (Frame 1) gas reaction ... 

Consider an open isothermal system where m internal irreversible processes related to a spontaneous evolution of several thermodynamic parameters a, occur simultaneously. The rate of energy dissipation in the system is given by the positively determined expression (2.5) ... 

In words An isothermal system is in equilibrium when its free energy is a minimum. All spontaneous processes in an isolated system involve a diminution in its free energy. 

SPONTANEOUS PROCESSES (SECTION 19.1) Most reactions and chemical processes have an inherent directionality They are spontaneous in one direction and nonspontaneous in the reverse direction. The spontaneity of a process is related to the thermodynamic path the system takes from the initial state to the final state. In a reversible process, both the system and its surroundings can be restored to their original state by exactly reversing the change. In an irreversible process the system cannot return to its original state without a permanent change in the sturoimdings. Any spontaneous process is irreversible. A process that occtu s at a constant temperatiu e is said to be isothermal. 

Indicate whether each statement is true or false, (a) AS for an isothermal process depends on both the temperature and the amount of heat reversibly transferred, (b) AS is a state function, (c) The second law of thermodynamics says that the entropy of the system increases for all spontaneous processes. 

There is one thing to notice about the signs on the electromotive force. Because AG is related to the spontaneity of an isothermal, isobaric process (that is, AG is positive for a nonspontaneous process, negative for a spontaneous process, and zero for equilibrium) and because of the negative sign in equation 8.21, we can establish another spontaneity test for an electrochemical process. If E is positive for a redox process, it is spontaneous. If E is negative, the process is not spontaneous. If E is zero, the system is at (electrochemical) equilibrium. Table 8.1 summarizes the spontaneity conditions. 

I he occurrence of a spontaneous explosion in a chemically reacting system is a complicated process. However, the events that lead to explosion can be characterized as being either of a branching chain or of a thermal nature. Branching-chain explosions occur in systems that react by a chain mechanism, the details of which allow the chain carrier concentration, and hence, the over-all reaction rate to increase without limit, even under isothermal conditions. Such a condition is possible only if one or more of the steps in the reaction chain results in a multiplication of chain carriers—i.c., X + A — Y + Z + , where X, F, and Z arc chain carriers. 

The analysis of these P(h) isotherms emphasises that stratified foam films are formed from both systems (I and II). A phenomenon not revealed so far is that spontaneous (under constant capillary pressure) and forced (under various capillary pressures) stepwise thinning can occur in the same single foam film. A question arises as to whether the film that acquired such a thickness is in thermodynamic equilibrium or is kinetically stabilised. It should be noted that these transitions occur only in the direction of increasing pressure, i.e. the process... 

As stated above, the free energy is the amount of work to be performed in building up, by some reversible and isothermal process, the double layers of the system. The formation of these double layers occurs spontaneously when the wall and the solution are brought into contact. Hence we can state, a priori, that the free energy of a double layer system must be a negatme quantity (work js gained by the formation). 

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