Nernst Equation
The and pH of a solution are related. For a half cell equation, conventionally written as reduction (electrons on the left side):
The half cell standard potential is given by:
where is the standard Gibbs free energy change, is the number of electrons involved, and is Faraday's constant. The Nernst equation relates pH and :
where curly brackets indicate activities and exponents are shown in the conventional manner. This equation is the equation of a straight line for as a function of pH with a slope of volt (pH has no units.) This equation predicts lower at higher pH values. This is observed for reduction of O2 to OH− and for reduction of H+ to H2. If H+ were on the opposite side of the equation from H+, the slope of the line would be reversed (higher at higher pH). An example of that would be the formation of magnetite (Fe3O4) from HFeO−
2 (aq):
3 HFeO−
2 + H+ = Fe3O4 + 2 H2O + 2 ]
where = −1.1819 − 0.0885 log[HFeO−
2] + 0.0296 pH. Note that the slope of the line is −1/2 the −0.05916 value above, since = −1/2.
Read more about this topic: Reduction Potential
Famous quotes containing the word equation:
“Jail sentences have many functions, but one is surely to send a message about what our society abhors and what it values. This week, the equation was twofold: female infidelity twice as bad as male abuse, the life of a woman half as valuable as that of a man. The killing of the woman taken in adultery has a long history and survives today in many cultures. One of those is our own.”
—Anna Quindlen (b. 1952)