Fe + hno3 = fe(no3)3 + no2 + h2o


In the oxidation number change method the underlying principle is that the gain in the oxidation number (number of electrons) in one reactant must be equal khổng lồ the loss in the oxidation number of the other reactant.

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Step 1. Write down the unbalanced equation ("skeleton equation") of the chemical reaction. All reactants & products must be known. For a better result write the reaction in ionic khung.

Step 2. Separate the process inkhổng lồ half reactions. A redox reaction is nothing but both oxidation & reduction reactions taking place simultaneously.

a) Assign oxidation numbers for each atom in the equation. Oxidation number (also called oxidation state) is a measure of the degree of oxidation of an atom in a substance (see: Rules for assigning oxidation numbers).

b) Identify & write out all redox couples in reaction. Identify which reactants are being oxidized (the oxidation number increases when it reacts) và which are being reduced (the oxidation number goes down). Write down the transfer of electrons. Carefully, insert coefficients, if necessary, to lớn make the numbers of oxidized & reduced atoms equal on the two sides of each redox couples.

c) Combine these redox couples into lớn two half-reactions: one for the oxidation, & one for the reduction (see: Divide the redox reaction into two half-reactions).

Step 3. Balance the atoms in each half reaction. A chemical equation must have sầu the same number of atoms of each element on both sides of the equation. Add appropriate coefficients (stoichiometric coefficients) in front of the chemical formulas lớn balance the number of atoms. Never change any formulas.

a) Balance all other atoms except hydrogene và oxyren. We can use any of the species that appear in the skeleton equations for this purpose. Keep in mind that reactants should be added only khổng lồ the left side of the equation & products to lớn the right.

b) Balance the charge. For reactions in an acidic solution, balance the charge so that both sides have sầu the same total charge by adding a H+ ion to lớn the side deficient in positive sầu charge.

c) Balance the oxygene atoms. Cheông chồng if there are the same numbers of oxygen atoms on the left và right side, if they aren"t equilibrate these atoms by adding water molecules.

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Balanced half-reactions are well tabulated in handbooks & on the web in a "Tables of standard electrode potentials". These tables, by convention, contain the half-cell potentials for reduction. To make the oxidation reaction, simply reverse the reduction reaction and change the sign on the E1/2 value.

Step 4. Make electron gain equivalent to electron lost. The electrons lost in the oxidation half-reaction must be equal the electrons gained in the reduction half-reaction. To make the two equal, multiply the coefficients of all species by integers producing the lowest comtháng multiple between the half-reactions.

Step 5. Add the half-reactions together. The two half-reactions can be combined just like two algebraic equations, with the arrow serving as the equals sign. Recombine the two half-reactions by adding all the reactants together on one side & all of the products together on the other side.

Step 6. Simplify the equation. The same species on opposite sides of the arrow can be canceled. Write the equation so that the coefficients are the smallest set of integers possible.

Finally, always kiểm tra to lớn see that the equation is balanced. First, verify that the equation contains the same type và number of atoms on both sides of the equation.

The difference between atoms on the left and right side of the equation is not equal to lớn zero.

The error most likely occurred while balancing atoms in the partial equations of oxidation and reduction (Step 3.a). You can resolve this by writing the equation in ionic size. For example, the program won"t correctly balance a equation such as Na2S2O3 + I2 = Na2S4O6 + NaI while the same equation with only NaI written in ionic khung (Na2S2O3 + I2 = Na2S4O6 + Na+ + I-) will be balanced with ease. Carefully Review the procedure. The wise man learns from the mistakes of others.

Balance the equation with the ARS method → Fe(NO3)2 + HNO3 = Fe(NO3)3 + NO + H2O.

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Citing this page:

Generalic, Eni. "Balancing redox reactions by oxidation number change method." EniG. Periodic Table of the Elements. KTF-Split, 22 Jan. 2021. Web. Date of access. .


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