Is there any trick to trimming? I m always not right

Least common multiple method: find the least common multiple of each atom before and after the reaction, so that the atom is the least common multiple before and after the reaction, generally starting with the oxygen atom first, and then balancing other atoms.

Observation method: Derive the stoichiometric number of the chemical formula of the reactant and the stoichiometric number of the product from a product with a more complex chemical formula, and then find the dump stoichiometry of other chemical formulas according to the stoichiometric number of the chemical formula obtained by the trousers, so that the balance can be achieved.

Use the least common multiple.

Method trimming: kclo kcl+o in this reaction is the right oxygen atom.

The number is 2, and the left is 3, then the least common multiple of the state Qingzhao is 6, so the coefficient before kclo should be matched with 2, and the coefficient before O2 should be matched with 3, and the formula becomes:

2kclo kcl+3o, since the number of potassium atoms and chlorine atoms on the left becomes 2, then the coefficient of 2 should be matched before kcl, ** is changed to an equal sign, indicating the condition that is:

2kCl ==2kCl+3O (The reaction condition is manganese dioxide.)

Catalysis and heating. "mno" is written above the equal sign; "Heat" is written below the equal sign, and a triangle can be used.

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Least common multiple method: (1) Find the least common multiple of each atom before and after the reaction; (2) make the atom the least common multiple before and after the reaction; (3) Generally, start with the oxygen atom first, and then balance the other atoms. Observation:

1) Deriving the stoichiometric number of the chemical formula of the reactant and the stoichiometric number of the product from a product with a complex chemical formula; (2) According to the stoichiometric number of the chemical formula obtained, and then find out the dumping metering number of other chemical formulas, and the Qingpeng can be balanced.

1.First, find the element with the largest number of atoms at the left and right ends of the chemical equation and find their least common multiple.

2.Second, divide this least common multiple by the number of atoms on the left and right sides of the state, and the quotient is the stoichiometric number of the chemical formula in which they are located.

3.Then, according to the stoichiometric number of the determined chemical formula of the substance, the stoichiometric number of the chemical formula is derived and calculated until the chemical equation is balanced.

Find the key chemical formula in the chemical equation, set the number before the chemical formula as 1, and then balance the number before the other chemical formulas 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 extrapolate in turn.

The method of balancing is as follows:

1. First find out the element with the largest number of atoms at the left and right ends of the reaction formula, and find their least common multiple. Secondly, divide this least common multiple by the original number of atoms on the left and right sides, and the quotient obtained is the coefficient of the chemical formula in which they are located.

2. Then, according to the coefficients of the determined chemical formula of the substance, the coefficients of its chemical formula are deduced and calculated until the equation is balanced.

3. Finally, verify the reaction formula. Whether the trim is correct or not.

Trim method:

1. Least common multiple method.

2. Odd spouse number method.

The sum of two odd numbers or two even numbers is even; The sum of the odd number and the even number is the odd number - abbreviated as the addition rule. The product of odd and even numbers or two even numbers is even; The product of two odd numbers is still an odd number – the multiplication rule for short.

3. Algebraic method.

The algebraic method is also called the undetermined coefficient method, and its method steps are as follows. Firstly, the unknowns such as a, b, c, and d are set as the coefficients of the chemical formulas at both ends of the chemical equation to be balanced. Then, according to the law of conservation of mass, the atomic type and number of atoms of each element before and after the reaction must be equal, the atomic number and chemical formula coefficient of each element are listed.

4. Electronic gain and loss method.

The principle of the electron gain and loss method is that in the oxidation-reduction reaction, the total number of electrons lost by the reducing agent must be equal to the total number of electrons gained by the oxidant. According to this rule, the equation for the oxidation-reduction reaction can be trimmed.

Chemical equation trim methods and techniques.

1.This method is suitable for common chemical equations that are not very difficult. For example, in this reaction formula, the number of oxygen atoms on the right is 2, and the number of oxygen atoms on the left is 3, so the least common multiple is 6, so the coefficient before kclo3 should be 2, and 02 should be preceded by 3, and the formula becomes:

2KCI03-KCl+302, because the number of potassium atoms and chlorine atoms on the left becomes 2, then the coefficient of KCl should be matched before 2, ** is changed to an equal sign, and the conditions are indicated, namely: 2KC03==2KCl+302

2.Odd-even matching.

This method is suitable for multiple occurrences of an element on both sides of the chemical equation, and the total number of atoms of the element on both sides is odd and even, for example: C2H2+02-CO2+H20, and the balance of this equation starts with the oxygen atom with the highest number of occurrences first. There are 2 socks in O2 to initiate oxygen atoms, regardless of the coefficient before the chemical formula, the total number of oxygen atoms should be even.

Therefore, the coefficient of H20 on the right should be matched with 2 (if other molecular coefficients appear as fractions, it can be matched with 4), from which it can be deduced that the first 2 of C2H2 becomes: 2C2H2+02==C02+2H2O, from which it can be seen that the coefficient before CO2 should be 4, and the final element O2 is 5, and the conditions can be specified: 2C2H2+502==4C02+2H200

3.Observational trimming.

Sometimes there will be a substance with a more complex chemical formula in the equation, we can deduce the coefficients of other chemical formulas through this complex fraction, for example: Fe +H20--Fe304+H2, Fe304 chemical formula is more complex, obviously, Fe ** in Fe3O4 is in elemental Fe, O comes from H2O, then Fe is preceded by 3, H20 is preceded by 4, then the formula is: Fe + 4H20 = Fe304 + H2 From this, the H2 coefficient is 4, indicating the conditions, ** Change to an equal sign:

3fe+4h20==fe304+4h2

Observation method, fixed one method, electronic conversion hair.

The trimming of chemical equations is an important content, but also a difficult point. The commonly used methods of chemical equation balancing in junior high school mainly include: observation method, least common multiple method, odd spouse method, etc. Next, we introduce a method for leveling chemical equations, the fractional method.

The steps to trim the chemical equation of the fractal modulus method are:

1) First, on the side of the elemental existence, select a more complex chemical formula, and assume that the coefficient of this chemical formula is 1.

2) Match the number of atoms of elements other than elemental elements by an appropriate coefficient (which can be a fraction) in front of the other chemical formulas.

3) Then, the number of atoms of the elemental element is balanced by an appropriate coefficient (which can be a fraction) in front of the elemental chemical formula.

4) Finally, the coefficients before each chemical formula in the equation are enlarged by an appropriate multiple at the same time, and the denominator of the number of code clusters in each system is removed, and the chemical equation is balanced.

Example 1Trim Chemical Equation:

Analysis: The element appears on the side of the reactant, we assume that the coefficient is 1, observe the number of C and H atoms on the left and right sides of the equation, match the coefficient 2 in front, and the front coefficient 1 remains unchanged, then the number of C and H atoms on the left and right sides has been balanced.

Retrim the number of o atoms. If the number of o atoms on the right side of the equation is 5, then it should be preceded by coefficients.

Finally, go to the denominator. Expand the coefficients in front of each chemical formula in the equation by a factor of 2 at the same time, and the chemical equation is balanced.

Example 2Trim Chemical Equation:

Analysis: Elemental matter appears on the side of the product, assuming a coefficient of 1, and the number of C and O atoms is balanced first. Namely:

Retrim the number of Fe atoms.

Finally, go to the denominator.

Note: For some reactions with elemental participation or generation, especially the reaction between substances and oxygen, the application of fractional method can often make the chemical equation quickly balanced. However, the fractional method also has certain limitations, and it is not very applicable to the reaction that there are no elemental substances in the reactants and products, or for complex reactions where there are more than two types of reactants or products.