Spontaneous processes reactions

If there are no reactions, the conservation of the total quantity of each species dictates that the time dependence of is given by minus the divergence of the flux ps vs), where (vs) is the drift velocity of the species s. The latter is proportional to the average force acting locally on species s, which is the thermodynamic force, equal to minus the gradient of the thermodynamic potential. In the local coupling approximation the mobility appears as a proportionality constant M. For spontaneous processes near equilibrium it is important that a noise term T] t) is retained [146]. Thus dynamic equations of the form... 

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. 

If AG is equal to 0, the process is at equilibrium, and there is no net flow either in the forward or reverse direction. When AG = 0, A.S = H/T, and the enthalpic and entropic changes are exactly balanced. Any process with a nonzero AG proceeds spontaneously to a final state of lower free energy. If AG is negative, the process proceeds spontaneously in the direction written. If AG is positive, the reaction or process proceeds spontaneously in the reverse direction. (The sign and value of AG do not allow us to determine how fast the process will go.) If the process has a negative AG, it is said to be exergonic, whereas processes with positive AG values are endergonic. 

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... 

Perhaps the simplest way to define spontaneity is to say that a spontaneous process is one that moves the reaction system toward equilibrium. A nonspontaneous process moves the system away from equilibrium. 

Coupled reactions are common in human metabolism. Spontaneous processes, such as the oxidation of glucose,... 

Second law of thermodynamics A basic law of nature, one form of which states that all spontaneous processes occur with an increase in entropy, 457 Second order reaction A reaction whose rate depends on the second power of reactant concentration, 289,317q gas-phase, 300t... 

Write a balanced reaction for the spontaneous process when we allow a path for electron flow between the O2/H2O electrode and the H /H20 electrode as described in Section 5.3.3. 

C14-0117. The notion of thermodynamic coupling of a nonspontaneous process with a spontaneous process is not restricted to chemical reactions. Identify the spontaneous and nonspontaneous portions of the following coupled processes (a) Water behind a dam passes through a turbine and generates electricity, (b) A gasoline engine pumps water from a valley to the top of a hill. 

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). 

It is observed that the spontaneous process takes HC1 from a greater activity (or concentration) to a lesser activity (or concentration). If, for instance, c2 is greater than Cj and therefore (a )2 is greater than ( )j, the emf will be positive and the reaction will advance in the direction in which it is expressed. One can apply such concentration cells to ascertain the activity of an electrolyte at one concentration, or in a solution having other ions compared with the activity of an electrolyte in another solution. 

Gas-phase ion chemistry is a broad field which has many applications and which encompasses various branches of chemistry and physics. An application that draws together many of these branches is the synthesis of molecules in interstellar clouds (Herbst). This was part of the motivation for studies on the neutralization of ions by electrons (Johnsen and Mitchell) and on isomerization in ion-neutral associations (Adams and Fisher). The results of investigations of particular aspects of ion dynamics are presented in these association studies, in studies of the intermediates of binary ion-molecule Sn2 reactions (Hase, Wang, and Peslherbe), and in those of excited states of ions and their associated neutrals (Richard, Lu, Walker, and Weisshaar). Solvation in ion-molecule reactions is discussed (Castleman) and extended to include multiply charged ions by the application of electrospray techniques (Klassen, Ho, Blades, and Kebarle). These studies also provide a wealth of information on reaction thermodynamics which is critical in determining reaction spontaneity and availability of reaction channels. More focused studies relating to the ionization process and its nature are presented in the final chapter (Harland and Vallance). 

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). 

As a new criterion for reaction spontaneity, we say AS(totai) must be positive. We must consider the surroundings if we are to understand how the overall extent of energetic disorder increases during a process. 

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... 

When the cyclic acetylene 260 is generated from a suitable precursor, it undergoes an isomerization reaction spontaneously generating naphthalene (263) and benzo-fulvene (264) as the finally isolable products. Very likely the process begins with a retro-Diels-Alder reaction to the [3]cumulene 261, which in a cascade reaction via the semicydic allene 262 rearranges to 263 and 264 [111]. 

Upon excitation of a semiconductor, the electrons in the conduction band and the hole in the valence band are active species that can initiate redox processes at the semiconductor-electrolyte interface, including photocorrosion of the semiconductor, a change in its surface properties (photoinduced superhydrophilicity [13]), and various spontaneous and non-spontaneous reactions [14-19]. These phenomena are basically surface-mediated redox reactions. The processes are depicted in Fig. 16.1. Owing to the slow spontaneous kinetic of the reactions between the... 

On the other hand, abzymes are generally able to accelerate reactions by at most 107 times the rate of the spontaneous process. It has to be said that scientists at large are looking for a major step forward in antibody catalysis to achieve rate accelerations up to 109 that would establish abzymes as a feature of synthetically useful biotransformations. At the same time, it is essential to demonstrate that product inhibition is not an obstacle to the scaled-up use of abzymes. 

Reaction mixtures containing an arylnitramine with an o-nitro group require careful work-up because the formation of diazophenols is often a facile and sometimes spontaneous process. The... 

Discussion.— It will be observed that, within the hmits of error, appears at the same ionization potential as H+. Since, as has been stated, the amoimt of H3+ increases with respect to H+ with increase of pressure, it is natural to assume that H3+ is formed by the combination of with the neutral H2 molecule, a spontaneous process which occms with the evolution of energy. From energy considerations, it is possible that an H2" , sufficiently accelerated, could, upon colHsion with an H2 molecule, break up to form either H+ or H3+, yet the results here obtained indicate that no such reaction takes place to any detectable extent. If such a process took place we should expect to find either or H3 at 15.7 volts, which is the ionization potential for the formation of the H2+. In no case w or H3+ found below 16.5 volts. At higher pressures, where the probability of collision is greater, such a phenomenon might appear. 

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