Trim method Specific 5, what are the trimming methods

Here's how:

1. Trim coefficient, the coefficient of each chemical formula in the balancing chemical equation.

2. Change the single line to a double line, which is the most easily ignored part of the chemical equation.

3. If a reaction occurs in the solution, there is no solid in the reactant, and there is a precipitate in the product, it is indicated by a "" sign on the right side of the chemical formula of the precipitate generated; There is no gas in the reactant, and if there is gas in the product, it is indicated by a " " sign on the right side of the gas generated; If both the reactant and the product have gases, there is no need to add any symbols.

Concise trimming method for disproportionation reactions

The three valence states are marked first, and the two are subtracted by the third line. If there is an approximation that needs to be shortened, it will be completed by leisurely observation.

Explanation: 1. The three valence states are labeled first: it means that the first step of the simple and quick trim method of the disproportionation reaction is to first mark the valency of the molecules of different substances in the reaction formula and the elements in the disproportionation reaction.

For example: s(0)+koh k2s(-2)+k2s(+4)o3+h2o.

2. Subtract the third system from the two: It means that the change value (absolute value) of any two valences is the coefficient of the third party.

3. If there is a divisibility, it needs to be reduced: it means that if there is a common divisor of the three coefficients obtained from the second step, it needs to be reduced and then added to the reaction formula.

According to the poetic requirements, the analysis is as follows:

In S and K2S, S(0) S(-2), the valency change value is 0-(-2) = 2, so the coefficient before K2SO3 is 2.

In S and K2SO3, S(0) S(+4), the valency change value is 0-4 = 4, so the coefficient before K2S is 4.

In K2S and K2SO3, S(-2) S(+4), the valency change value is (-2)-4 = 6, so the coefficient before S is 6.

And because there is a common divisor 2, the reduction is , and the reduced coefficient is substituted into the reaction formula: 3S+KoH 2K2S+K2So3+H2O.

4. Leisurely observation is complete: It means that after substituting the reduced coefficient into the reaction formula, you can balance it by observing it leisurely.

Observation shows that the right side is 6 K, so 6 should be added before KOH, and 6 should be added to the left after adding 6, so 3 should be added before H2O, so the chemical reaction equation after trim is obtained: 3S+6KOH = 2K2S+K2SO3+3H2O.

Equation trim for chemical reactions.

a) Least common multiple method.

This method is suitable for common chemical equations that are not too 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, then the least common multiple is 6, so the coefficient before kclo3 should be matched with 2, and the coefficient before O2 should be matched with 3, and the formula becomes: 2kclo3 KCl+3O2, since the number of potassium atoms and chlorine atoms on the left becomes 2, then the coefficient 2 before KCL, ** is changed to equal sign, indicating the condition is:

2kclo3==2kcl+3o2↑

2) Odd-even equalization.

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+O2 - CO2+H2O, and the balance of this equation starts with the oxygen atom with the highest number of occurrences. There are 2 oxygen atoms in O2, and the total number of oxygen atoms should be even, regardless of the number of coefficients before the chemical formula.

Therefore, the coefficient of H2O 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+O2==CO2+2H2O, from which it can be seen that the coefficient before CO2 should be 4, and the final coefficients with elemental O2 are 5, and the conditions can be specified:

2c2h2+5o2==4co2+2h2o

c) Observational balancing.

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 molecule, for example: Fe + H2O - Fe3O4 + H2, Fe3O4 chemical formula is more complex, obviously, Fe3O4 Fe** in the elemental Fe, O comes from H2O, then Fe is preceded by 3, H2O is preceded by 4, then the formula is: 3Fe + 4H2O Fe3O4 + H2 This deduces that the H2 coefficient is 4, indicating the conditions, ** Change to an equal sign:

3fe+4h2o==fe3o4+4h2↑

4) Normalization Law.

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.

Step 1: Let the coefficient of nh be: 1 1nh +o - no+h o

Step 2: Trim the h atom, from which we get: 1NH+O - NO+3 2HO

Step 3: The coefficient of the left end O is deduced from the total number of oxygen atoms at the right end: 1nh +5 4o - no + 3 2 h o

Step 4: Multiply the denominator by the least common multiple: 4nh + 5o = 4no + 6h o

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.

Least common multiple method: kclo kcl+o In this reaction formula, the number of oxygen atoms on the right is 2, and the left is 3, then the least common multiple is 6, so the coefficient before kclo should be matched with 2, and O2 should be preceded by 3, and the formula becomes: 2kclo kcl+3o, because the number of potassium atoms and chlorine atoms on the left becomes 2, then the coefficient 2 should be matched before kcl, ** is changed to equal sign, and the condition is indicated, that is:

2kCl ====2kCl+3O (The reaction conditions are manganese dioxide catalysis and heating.) "mno" is written above the equal sign; "Heating" is written below the equal sign, and the triangle " " can be used instead).

The chemical reaction equation strictly adheres to the law of conservation of mass, and after writing the chemical reaction equation and writing the reactants and products, the number of atoms on the left and right sides is often not equal, and the law of conservation of mass is not satisfied, which needs to be solved by calculating the balance.

Two principles are followed:

The law of conservation of mass (In a chemical reaction, the type of atom before and after the reaction does not change, the number does not increase or decrease, and the mass of the atom does not change. ）

The redox reaction looks at the rise and fall of the valency, the number of electrons transferred, and the number of atoms on both sides should be equal, and other reactions are like this.

This thing depends on experience. The theories in books still have to be obtained through countless experiments by themselves. In a word, redox reaction is to look at the number of electrons transferred by a substance.

Carry out balancing to see the rise and fall of the valence of the substance. The non-redox reaction is the metathesis reaction, which is the exchange of each other, and it is enough to pay attention to the valency.

It is recommended that you go to the Internet to find some information in this area and read carefully, there are many skills, not one sentence or two sentences can be said clearly.

The main thing depends on whether the number of atoms before and after the reaction is flat? There are many ways to do this...