An exergonic reaction is a chemical reaction where the change in the free energy is negative (there is a net release of free energy),[1] indicating a spontaneous reaction. For processes that take place under constant pressure and temperature conditions, the Gibbs free energy is used whereas the Helmholtz energy is used for processes that take place under constant volume and temperature conditions.
Symbolically, the release of free energy, G, in an exergonic reaction (at constant pressure and temperature) is denoted as
{\displaystyle \Delta G=G_{\rm {products}}-G_{\rm {reactants}}<0.\,}
Although exergonic reactions are said to occur spontaneously, this does not imply that the reaction will take place at an observable rate. For instance, the disproportionation of hydrogen peroxide is very slow in the absence of a suitable catalyst. It has been suggested that eager would be a more intuitive term in this context.[2]
More generally, the terms exergonic and endergonic relate to the free energy change in any process, not just chemical reactions. An example of an exergonic reaction is cellular respiration. This relates to the degrees of freedom as a consequence of entropy, the temperature, and the difference in heat released or absorbed.
By contrast, the terms exothermic and endothermic relate to the overall exchange of heat during a process
See the image below.
An excited electron is in a <em>high-energy state</em>.
When it drops to the lower-level ground state, it must get rid of this excess energy by <em>emitting it</em> as a quantum of light.
The number of electrons in the outermost shell of an atom determines<span> its </span>reactivity<span>.</span><span>
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Au³⁺ metal ion is reduced in the Au/Cr cell and Co²⁺ metal ion is reduced in the Co/Zr cell
<h3>What is a voltaic cell?</h3>
A voltaic cell is a cell that generates electricity by a spontaneous redox reaction.
It is an electrochemical cell, also known as a galvanic cell and
Electrical energy is created by converting chemical energy.
Examples of voltaic cells include the dry cell, nickel-cadmium cell, lead storage cell, and fuel cells.
The half-cell reactions for each cell are given by
; E° = 1.50 V
; E° = –0.74 V
; E° = –0.28 V
E° = –0.76 V
Thus, Au³⁺ is reduced in the Au/Cr cell and Co²⁺ is reduced in the Co/Zr cell
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