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Predicting redox reactions

The redox reaction between two chemical species depends on the relevant strengths of the reductants and oxidants. The direction of the reaction can be estimated from a reactivity series that ranks molecules by their strength as oxidizing or reducing agents or calculated from the redox potential.

From a reactivity series, the more reactive molecule will undergo the reduction reaction while the other molecule undergoes the oxidation reaction.

For a more mathematical approach, the redox potential can be used. If the cell potential is calculated using the formula

ECell = ECathode - EAnodethe electric potential of the cell equals the electric potential of the cathode minus the one from the anode .

is positive, this means that the reaction will occur spontaneously and potential energy will be released. The energy released through these reactions is converted into a different form of energy, such as heat. A negative potential means that the reaction requires energy to proceed and it will not occur spontaneously.

Copper and silver redox reaction. Illustration of a test tube containing solid copper in contact with a solution of silver nitrate. There are three stages of the reaction labeled 1, 2, and 3. In the first stage test tube, two arrows point out doing a small zoom into the components, showing the difference in the silver, nitrate, and copper ions. In stage two, copper has oxidized and started losing electrons, and silver is reduced, which makes the liquid turn blue. In the third stage, the copper starts reacting with the nitrate ions forming copper nitrate and the silver ions are agglomerating around the copper plate. The reaction is also written: as reactants, 2 molecules of silver nitrate in aqueous form and one atom of copper in solid form, forming copper nitrate in aqueous form and two atoms of silver in solid form.

Figure 1: Redox reaction between copper (Cu) and silver (Ag). Copper is the stronger reducing agent and silver is the stronger oxidizing agent in the reactivity series and the potential for the reaction Cu + 2Ag(NO3)→ Cu(NO3)2 + 2Ag is E = 0.8-0.34 = +0.46V. where one atom of copper and two molecules of silver nitrate react to produce one molecule of copper nitrate and two atoms of silver is 0.8 minus 0.34, which results in electric potential of 0,46 volts.