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Write an essay on electrode potentials.

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Introduction

F7 Essay Writing (Electrode Potentials) Q. Write an essay on electrode potentials. Outlines: (I) What are electrode potentials? (a) associated with equilibria of redox systems (half cells): e.g. metal / metal ion system ; non-metal / ion system ; ion / ion system; (b) reactivity, tendency for reduction to occur (losing electrons) and potential difference; (c) the potential difference of a half cell cannot be measured alone, but a relative value could be measured with another reference half cell / reference electrode; (d) a standard hydrogen electrode [SHE] (in which the emf is defined as zero) is used as the reference electrode; (II) How are electrode potentials measured? (a) concentration, temperature and pressure affect the emf of SHE, and the standard electrode potentials are obtained under conditions of 298K, 1 atm and conc. of 1M. (b) set up a cell with SHE and a salt bridge of electrolyte (e.g. KNO3); (c) a potentiometer is used to measure the cell emf (maximum potential difference), and the sign of cell emf = polarity of the right hand electrode. (III) How are electrode potentials used? / Application of electrode potentials? ...read more.

Middle

For example, magnesium is more reactive than copper, so that Mg forms Mg2+ and gives out electrons more readily than Cu does. From an equilibrium point of view, Mg2+ + 2 e- Mg (eqn. 2) Cu2+ + 2 e- Cu (eqn. 3) the position of magnesium equilibrium lies further to the left than that of copper equilibrium. Therefore, a greater potential difference will be observed in the case of magnesium since there is a greater difference between the "negativeness" of magnesium electrode and the "positiveness" of the solution around it. How are electrode measured? The potential difference between the metal and solution cannot be measured directly. Instead, it is measured by comparison with a reference electrode: standard hydrogen electrode (SHE), the potential of which is defined as zero. As the equilibrium position can be altered by changing temperature, pressure and concentation, the standard conditions of SHE are defined as 298K, 1atm and 1M H+ concentration. In order to measure the electrode potential of an electrode system, SHE is connected with the electrode system to be studied. ...read more.

Conclusion

while copper serves as the cathode (positive one). The electrode potentials of half cells could be used to determined the E? value of electrochemical cell by simple calculation: (eqn. 4) Besides, electrode potentials are one way of measuring how easily a substance loses electrons. Thus, it is possible to predict the feasibility of redox reactions from the corresponding electrode potentials: redox reactions with a positive value are energetically feasible. However, apart from predicting the reaction feasibility, it is also noticeable that the value does not tell anything about how fast the reaction will happen unless kinetic information (e.g. activation energy) are given. In addition, the prediction is only valid under standard conditions, i.e. 298K, 1 atm and 1.0M concentrations for all species. In conclusion, the electrode potentials give us a way of comparing the position of redox equilibrium when substances lose electrons. In the fundamental electrochemical studies of different elements and compounds, it surely offers helpful information for us to know more about their reactivity as well as potential towards reduction. In addition to the calorimetric investigation of heat change of reaction, the electrode potentials is also a convenient tool for us to understand the relative energetic stabilities of substances. ?? ?? ?? ?? 1/4 ...read more.

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This is an extremely well explained report on electrochemical cells. The author explains how a cell works with incredible clarity and very helpful equations and diagrams. The paragraphs may seem long and slightly daunting, but are necessary for the author to get their point across.

Overall, this piece of work is 5 stars out of 5

Marked by teacher Brady Smith 10/04/2013

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