How to Balance the Chemical Equation in a Redox Reaction? Hope for answers

The conservation of electron gains and losses is superficially the "valence rise and fall conservation".

For example, the trim of the Au2O3+Na2S2O3+H2O---Au2O+Na2S4O6+NaOH reaction: the Au element decreases from +3 to +1, and the S element rises from +2 to +, that is, 1Molau2O3 decreases by 4 valence, and 1molNa2S2O3 rises by 1 valence, so the coefficient ratio of Au2O3 to Na2S2O3 should be 1:4, assuming that the coefficient of Au2O3 is 1:

au2o3 + 4na2s2o3 + h2o = au2o + 2na2s4o6 + naoh

Next, the coefficients for determining NaOH and H2O according to the conservation of Na and H should be :

au2o3 + 4na2s2o3 + 8h2o = au2o + 2na2s4o6 + 4naoh

Finally, the O atoms are checked: there are 23 O atoms on the left and right sides, which proves that the equation is balanced.

Another example: 3Cu + 8Hno3 (dilute) = = 3Cu (No3) 2 + 2 No (gas) + 4H2O

In the reaction, Cu:0-->2 loses two electrons.

Between N in dilute nitric acid and the resulting NO gas: N: +5-->2 to get 3 electrons.

The least common multiple of the gain and loss of electrons is 6, so if cu loses 6 electrons, the coefficient in front is 3, and the coefficient in front of no to get 6 electrons is 2, and the remaining elements are conserved, balanced, and equal signs are added.

Another copper and dilute nitric acid to form NO2

Cu + 4 Hno3 (concentrated) = = Cu (No3) 2 + 2 No2 (gas) + 2H2O

cu:0-->2 loses two electrons.

n:+5-->4 in hno3--no2 to get an electron.

The least common multiple is 2

So 1 before Cu, 2 before NO2, and the remaining elements are conserved and balanced. 】

To put it simply, according to the conservation of electrons of gain and loss, first mark the valence and then find the least common multiple, and then multiply the corresponding number in front of the corresponding element whose valence rises, for example: there is an element that has dropped by five and another has risen by a price, just in front of the price increase multiplied by five, that is, the coefficient before the reducing agent and oxidation products is multiplied by five in the observation (at this time, do not move the redox coefficient that has been matched), according to the situation, appropriate water, hydrogen ions, hydroxide ions (look at both sides), the ion equation can also be matched according to the conservation of charge Presumably, this needs to be handled flexibly.

In general, equalization is achieved by using the total number of electrons gained and lost to equalize. Take the simple reaction of sodium metal with chlorine gas as an example:

2Na+Cl2=2NaCl Find the total number of electrons gained and lost from the valency change. In the case of sodium: 0 to +1, losing an electron, in the case of chlorine:

0 to -1, one electron is obtained, but chlorine has a total of 2 atoms, so, chlorine gas gets a total of 2 electrons. According to the principle of equality of the total number of electrons gained and lost, sodium should also lose 2 electrons, so 2 should be placed in front of sodium and 2 before NaCl according to the observation method

OK. According to the law of conservation of electrons, complex redox reactions are balanced according to electron transfer. First, the valencies of each oxidant and reducing agent are marked, and then the difference is made, and then they are balanced according to their least common multiple.

The same means that the three equilibrium conditions can be balanced when they are satisfied. Conservation of electrons, conservation of atoms, conservation of electric charge.

The number of electrons gained and lost in the reaction is the same, otherwise the substance is charged. The oxidizing agent gains a few electrons, and the reducing agent loses a few electrons.

1. Three principles: Principle of conservation of electrons for gain and loss, principle of conservation of atoms, principle of conservation of electric charge.

2. General method: Valence rise and fall method combined with least common multiple method.

3. Trimming skills

1) Forward leveling method: start the leveling with the oxidant and reducing agent.

Scope of application: intermolecular redox reaction, redox reaction in which all elements participate, and the substances in the product are both oxides and reduction products.

2) Reverse balancing method: start balancing with redox products first.

Scope of application: self-redox reaction, a part of the reactant is oxidized or reduced.

3) Overall balancing: When there are several atoms or clusters of atoms of an element (mostly seen in organic reaction balancing) in a compound, it can be treated as a whole and priced as a whole according to the principle of algebraic sum of the valency of the elements in the compound.

4) Missing trim method.

If there are reactants or products in the given chemical equation that are not written, in the balance period, if the vacant substance does not gain or lose electrons, but only provides an acid, base, and neutral environment for the reaction, the elements with valence rise and fall can be balanced first, and finally the missing substance can be determined according to the conservation of charge and the conservation of atoms.

The redox reaction equation is balanced according to the balancing principle. Because there is a transfer of electrons in the redox reaction, the valency of the element must rise and fall, and the element whose valency can be increased or the substance containing the element is called a reducing agent, and vice versa is called an oxidant. The steps of balancing include matching from left to right, marking the price change, finding the change, finding the total number, and matching coefficient.

The redox reaction equation is balanced according to the balancing principle. Since there is a transfer of electrons in the redox reaction, the valency of the element must rise and fall, and the element with increased valency or the element containing the element'The substance is called a reducing agent, and vice versa is called an oxidizing agent. The steps of balancing include matching from left to right, marking the price change, finding the change, finding the total number, and matching coefficient.

The general steps of the redox reaction equation balancing (formula: standard valence, list gains and losses, find the total, match coefficient and check conservation).

1) Marked valence, indicating the valency of the valence elements before and after the reaction;

2) List the gains and losses, and list the change value of the valence;

3) Find the total number, find the least common multiple to make the total number of valence rises and falls equal;

4) Matching coefficient, determine the stoichiometric coefficients of oxidants, reducing agents or oxidation products and reduction products, and observe the method to balance the coefficients of other substances;

5) Check the conservation, check whether the mass, charge, and gain and loss electrons are conserved.

Basic principles: three conservation (conservation of electrons, mass, charge) conservation of electrons (the number of electrons lost is equal to the number of electrons lost) characteristics: in the redox reaction, the valence rises and falls, and the total value of the rise and fall is equal.

Essence: In the redox reaction, the total number of electrons gained by the oxidant is equal to the total number of electrons lost by the reducing agent.

2) Conservation of mass.

The type and number of atoms before and after the reaction remain unchanged.

3) Conservation of charge (ion equation).

For ionic reactions, the total number of charges carried by the anions and cations at both ends of the equation is equal.

Basic principles: three conservation (conservation of electrons, mass, charge) conservation of electrons (the number of electrons lost is equal to the number of electrons lost) characteristics: in the redox reaction, the valence rises and falls, and the total value of the rise and fall is equal.

Essence: In the redox reaction, the total number of electrons gained by the oxidant is equal to the total number of electrons lost by the reducing agent.

2) Conservation of mass.

The type and number of atoms before and after the reaction remain unchanged.

3) Conservation of charge (ion equation).

For ionic reactions, the total number of charges carried by the anions and cations at both ends of the equation is equal.

The trimming method of the redox reaction equation is as follows: the general method is to match from left to right, mark the beginning and final states before the valence of the changing elements, and use the observation method to balance the other elements, and check whether the balanced equation conforms to the law of conservation of mass. According to whether the reaction has the rise and fall of oxidation number, whether there is electron gain and loss and transfer, whether a chemical reaction belongs to oxidation or bending delay, whether it is a reaction of oxidation or bending.

Redox reaction equation'The balancing method is as follows: the general method is to match from left to right, mark the beginning and final states of the valence of the changing elements, use the observation method to balance other elements, and check whether the equation after balancing conforms to Qiqing's law of conservation of mass. According to whether the reaction has an oxidation number rise and fall, whether there is electron gain and loss and transfer, whether a chemical reaction is a redox reaction, whether it is a redox reaction.

Step 1: List "Oxidizing Agent", "Reducing Agent", "Oxidation Product" and "Reducing Product".

Step 2: Mark the valence state of the variable valence element and the rise and fall of the valence.

Step 3: Trim the number of electrons gained and lost.

Step 4: Trim the number of charges.

Step 5: Check, and write an equal sign.

Reduction-oxidation reaction refers to a chemical reaction in which the oxidation number of an element changes accordingly before and after the reaction. It consists of an oxidation reaction and a reduction reaction and adheres to the law of conservation of charge.

Redox reaction is an important reaction in chemical reactions. Combustion, respiration, photosynthesis in nature, chemical batteries, metal smelting, rocket launches, etc. in production and life are all closely related to this reaction. [

The redox reaction equation balancing method is the valence rise and fall method. However, for some complex equations, special balancing methods are required, such as the zero-valent method, the integral method, etc.

1. Trim principle:

The number of atoms of each element before and after the reaction is equal, i.e., the mass is conserved.

The total number of electrons gained by the oxidant is equal to the total number of electrons lost by the reducing agent, i.e., the electrons are conserved.

The total value of the decrease in the valency of the oxidant is equal to the total value of the increase in the valency of the reducing agent.

2. Trim steps:

Standard valence: Write the chemical formula of the reactants and products, and mark the valency of the valence element.

Column Changes: List the rise and fall of the valency of the elements before and after the reaction.

Find the Total: Equalize the total number of increases and decreases in valence.

Matching coefficient: use the method of observation to balance the stoichiometric number of other substances, and after balancing, change the single line to an equal sign.

Check conservation: Check whether the two sides of the equation are "conservation of mass" and "conservation of charge".

3. Some common simple methods are:

Least common multiple method: This method is suitable for common chemical equations that are not very difficult.

Parity Balance: This method is suitable for multiple occurrences of an element on both sides of a chemical equation where the total number of atoms of that element on both sides is odd and even.

Observational balancing: Sometimes there is a substance with a complex chemical formula in the equation, and we can use this complex molecule to deduce the coefficients of other chemical formulas.

Normalization method: Find the key chemical formula in the chemical equation, set the number before the chemical formula as 1, and then balance the number of stoichiometry before the other chemical formula according to the key chemical formula. If the measured number is a fraction, and then the measured number is multiplied by the same integer, and the fraction is turned into an integer, this balancing method in which the key chemical formula measurement number is 1 is predetermined, which is called the normalization method.

Method: Select the most complex chemical formula in the chemical equation, let its coefficient be 1, and then infer it in turn.

The above content reference: Encyclopedia: Redox reaction