How to learn how to trim chemical redox reactions

The method of trimming <> redox reaction consists of the following steps:1Determine the oxidation states of all elements in the reactants and products and list them to the left and right of the reaction equation.

2.Find the elements that need to be trimmed, and the inch-you-locust is generally oxygen and hydrogen. 3.

Start by equilibrating all the parts of the non-redox reaction. 4.To balance the amount of oxygen, add the appropriate H2O molecules on the side of the reactant and the product.

5.Equilibrium the amount of hydrogen by adding appropriate H+ ions (under acidic conditions) or OH- ions (under alkaline conditions) on both sides of the reactants and products. 6.

Determine the number of electrons transferred and their direction, and pair reactants with an equal number of electrons with the product. 7.Finally, check whether the balanced reaction meets the requirements of the chemical equation (conservation of mass, conservation of charge, etc.).

It should be noted that the redox reaction trimming method will be slightly different depending on the reaction conditions (acidic, alkaline, etc.), and the specific method needs to be determined according to the specific chemical reaction.

The principle of trimming for redox reactions.

1) Principle of conservation of electrons: the total number of electrons lost by the reducing agent in the reaction is equal to the total number of electrons obtained by the oxidant.

2) Principle of conservation of charge: if it is an ionic reaction, the total number of positive and negative charges carried by ions before and after the reaction is equal.

3) Principle of conservation of mass: the number of atoms of each element before and after the reaction is equal.

Trim steps: 1) A mark: indicate the valency of the elements whose valency has changed before and after the reaction.

2) Second-class: By finding the least common multiple, the total value of valence rise and fall is equal.

3) Three determinations: determine the stoichiometric number of oxidant and reducing agent.

Stoichiometric number of oxidant (reducing agent) = least common multiple of the price reduction (liter) The total number of oxidant (reducing agent) price reductions (liters) in 1mol.

4) Siping: Balance the stoichiometric numbers of other substances by observation method.

5) Five checks: check whether the mass is conserved with charge and electrons respectively.

The trimming of redox reaction is an important step in writing the redox reaction equation correctly, and its difficulty is generally not low, so mastering a good solution method and balancing quickly and accurately is the key to solving this kind of problem.

1. Conservation of Electrons:

1. Trim principle.

When a redox reaction occurs, the reducing agent loses electrons and the oxidizing agent gains electrons. Because the essence of the whole process is like the reducing agent giving electrons to the oxidizing agent, and between these losses and gains, the electrons are conserved.

2. Methods and steps.

Mark the valency of the elements that have changed, and determine the trim direction of the redox reaction.

In the time of balancing, it is necessary to determine the number of measurements of the substance on the other side of the equation first. Sometimes the number of the reactant on the left side of the equation is written first, and sometimes the number of the product on the right side of the equation is written first. The following principles are generally followed:

Autoredox reaction The measured number of the product is first trimmed; Partial redox reaction first trim the number of the product; In general, redox reactions can be balanced either by the number of products or by the number of reactants.

Lists the changes in valence increases. When more than one element is raised or decreased, the value of the valency change needs to be superimposed according to the ratio of the number of atoms of each element.

The number of measurements of a substance that changes in valence according to the conservation of electrons, trimming, and valence.

The number of measurements of the remaining substance is balanced according to the conservation of mass. Finally, and check that the trim is correct according to the conservation of mass.

2. Pending coefficient method:

1. Trim principle.

The law of conservation of mass tells us that when a chemical reaction occurs, the number of atoms of each element of each substance in the reaction system is equal before and after the reaction.

2. Methods and steps.

Step 1: Analyze the valence increase.

Step 2: Swap the coefficient of the price increase.

Step 3: Cross the bridge (double-lane bridge).

Step 4: Find the elements that are not participating in the redox reaction and add them to the coefficient. Except (oxygen, hydrogen).

Step 5: Trim hydrogen.

Step 6: Check whether the oxygen is level.

Step 7: Perfection (add reaction conditions, add equal sign, add down arrow, approximate common divisor).

The difference between a redox reaction and a non-redox reaction is whether there is a transfer or loss of electrons in the reaction. The so-called redox reaction equation balancing is to determine the stoichiometric number of each species before and after the reaction under the premise of considering electron migration. In essence, this type of trim is also an inferential process for determining the number of atoms and molecules before and after a reaction based on the law of indestructibility of matter.

In this inference process, it is certainly not easier to use the more abstract valency as a tool to analyze the problem than to directly consider the number of electrons and atoms gained and lost, because the physical meaning of the latter is clearer and it is easier to relate to the number of molecules.

There are two main effective methods:

1. Trim according to the characteristics of redox (mainly conservation of electrons), suitable for two-element redox or disproportionation reactions.

1'According to the redox element trim, mark the valency before and after the redox atoms, use a double-line bridge to indicate the valency rise and fall (i.e., the number of lost electrons), and then find the least common multiple, and then divide the least common multiple by the rising and falling number, and exchange to obtain the coefficient.

2'According to the molecular trim of redox, mark the algebraic sum of the valency of the elements in each molecule, find the least common multiple, divide by the algebraic sum, and exchange to obtain the coefficient.

2. Trim according to the law of conservation of mass (general method), but the amount of calculation is large, and it is usually only used for equations that are difficult to balance.

1'Set the coefficients of each item as unknowns, then list the system of equations (usually indefinite equations) according to the conservation of atoms, and then substitute the relationship with the least unknown number into the chemical equation to minimize the coefficients.

2'Because the computational amount of the previous method is particularly large, the "one" method can be adopted to set the coefficient of the first term as one, and then set the coefficients of the other terms, solve the system of equations, and finally reduce the coefficient to the minimum.

Note: For chemical equations where the reactants and products are the same, the results of the trim are not necessarily the same

Observe the change in valency. Balance is carried out using the principle of conservation of charge.

1.Visual Inspection, 2The valence of positive and negative is equal.

Trimming of the redox reaction equation.

1. To master the balancing principles and steps of redox reaction equations, we should pay attention to the connection between old and new knowledge, that is, closely integrate with the basic concepts of redox reactions and the reactions between elemental compounds.

2 To master the trimming method of the redox reaction equation, you should pay attention to remember some typical examples and reactions.

The main points of knowledge are concise.

Trimming of the redox reaction equation.

1) Trim basis: In the redox reaction, the total number of valence rises and falls of the elements is equal, that is, the total number of electrons gained and lost is equal; the law of conservation of mass, that is, the sum of the masses of the substances participating in the reaction is equal to the sum of the masses of the substances formed after the reaction; Conservation of charge, i.e., when the redox reaction equation is expressed by the ion equation, the total number of charges carried by each ion before and after the reaction is equal.

2) Trim step: Standard valence, that is, mark the valence state of the elements whose valency changes in the reaction, and the standard valence is the lead; Column change, that is, finding the valence change value of the same element at both ends of the equation, column change is the basis; Finding the multiple, that is, finding the least common multiple of the decreasing value of the elemental valency in the oxidant and the increase value of the element valency contained in the reducing agent, by adjusting the stoichiometric number, so that the total number of valence rises and falls is equal, and finding the multiple is the key; The stoichiometric number of other substances is determined by the observation method according to the conservation of mass or charge, and the overall trim should be comprehensive.

3) Trimming skills: First change ** to equal sign When determining the stoichiometric number of oxidants, reducing agents, oxidation products and reduction products, there are all variation left matching (or forward trimming), self-changing right matching (or reverse trimming), partial change on both sides, and multiple variations to find the overall matching.

4) Types of trim: In addition to general trimming, there are letter trimming and missing trimming for redox reaction equations.

The most difficult points are dialed.

Focus】 Principles and steps of redox reaction equation balancing.

Difficulty】 Methods and techniques of redox reaction equation balancing.

Error-prone point] When the valency change of the element in the reaction is more than two, the valency change value cannot be found.

Start with the simple ones. Then with a variety of them, the main thing is to figure out the valence of no element.