Spontaneous process cells

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. 

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. 

Concepts Protocells Amphiphilic molecules spontaneously form cell-like structures that, by a process of encapsulation, acquire a chemical inventory... 

Cell Line A defined population of cells which has been maintained in a culture for an extended period and which has usually undergone a spontaneous process of transformation conferring an unlimited culture lifespan on the cells. 

The energy available from spontaneous cell reactions can be used to power vehicles or generate electricity (Box 12.2). To calculate the standard cell potential for a spontaneous process, we must combine the standard potential of the cathode half-reaction (reduction) with that of the anode half-reaction (oxidation) in such a way as to obtain a positive... 

Respiration and fermentation are two complex biological processes whose net ArG° values are negative and thus both represent spontaneous processes that can provide energy for cells to do work. Respiration is the reaction of glucose with O2 to form CO2 and H20. The net reaction can be represented as... 

The immortalization of a cell line can be accomplished as a spontaneous process, by an oncogene or virus or by chemical treatment. This can lead to a continuous cell line that can be propagated for an undetermined period. If such changes occur with an affect on cell cycle control, the cell line can be designated a transformed cell line. 

In other words, E is the electromotive force (EMF) of the reaction cell, where the voltage of the cell is unique for each reaction couple. Spontaneous processes have a negative free energy consequently, an electrochemical process will have a positive EMF. 

If a voltaic cell is to run spontaneously, the reduction potential at the cathode must be higher (more positive) than the reduction potential at the anode. This will allow the reaction at the anode to proceed as an oxidation (rather than a reduction). The greater the difference in potentials between the cathode and anode, the greater the cell voltage. Eor E° will be positive for spontaneous processes and negative for nonspontaneous ones. 

In Chapter 17, we showed the relationship between free energy and the spontaneity of a reaction. If you recall, a negative value for A G indicated a spontaneous reaction. In the last section, we saw that a positive cell voltage, or emf, indicates a spontaneous process. The free energy and emf can be related in Equation 18.3, which states... 

The over-all reduction of CO2 to CH4 is expected to be a spontaneous process that goes through the reduction levels of formate, formaldehyde, and methanol with only a limited, perhaps early requirement for activation by ATP. At the lowest reduction stages, extra ATP may even be generated. In the fermentation of methanol by M. barkeri which utilizes only the last reduction step for methane formation (Reaction 12) somewhat more than 1 mole of ATP appears to be generated for each mole of CH3OH oxidized to CO2, judging from cell yields (14). 

Note This balanced equation corresponds to the cell notation given. The spontaneous process is the reverse of this reaction. 

This is the direction of the spontaneous standard cell reaction that could be used to study the reverse of the given solubility equilibrium. A cell diagram for this favorable process is Ag(s) AgBr(s) I Br" (aq) Ag (aq) Ag(s)... 

Active transport is the process in which a substance is transferred from a region of lower concentration to one of higher concentration. This is a nonspontaneous process and must be coupled to a spontaneous process, such as the hydrolysis of ATP. The concentrations of ions in the blood plasma and in nerve cells are 15 mM and 400 mM, respectively (1 mM = 1 X 10 M). Use Equation (18.9) to calculate AG for the process at the physiological temperature of 37°C ... 

Although a positive value of °ceU indicates a spontaneous process, it is more revealing to consider the corresponding value of AG° (equation 7.9). The latter takes into account the number of electrons transferred during the reaction, as well as the magnitude and sign of the cell potential. For... 

Relating a spontaneous process to the sign of the cell potential (692) ... 

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