High School Chemistry Equation Trimming Method, High School Chemistry Equation Trimming Method and T

Observational method. It is directly by observing reactants and products, and balancing according to the law of conservation of mass and the law of conservation of atoms.

Valence lifting method.

This method is suitable for the balancing of redox reaction equations. Which element in the reactant increases its valence and which element decreases its valence is marked first, and then balanced according to the conservation of electrons.

Trim the redox reaction equation with the ionic-electron method.

In addition to the valency rise and fall method for redox reactions in aqueous solution, ion-electron method is generally commonly used for leveling. The distribution plain is that the total number of electrons gained by the oxidant during the reaction is equal to the total number of electrons lost by the reducing agent.

Now illustrate the trim steps with the following example.

In an acidic medium, KMno4 reacts with K2SO3 to form MnSO4 and K2SO4, which are balanced by this chemical equation.

The specific steps for trimming are as follows:

1) Write the unbalanced ion equation according to the reaction.

2) Write two semi-reactive formulas, one for the reaction in which the reducing agent is oxidized and the other for the reaction in which the oxidant is reduced:

The number of oxygen atoms in the product is more than that in the reactant, and the reaction is carried out in an acidic medium, so H2O can be added to the reactant in the above formula, H+ is added to the product, and then the balance of the atomic number and charge number of each element can be obtained

In the formula, the number of oxygen atoms in the product decreases, and enough hydrogen ions (2 times the number of oxygen atoms decreased) should be added to make it combine into water, and after trimming, it gets:

3) According to the principle of equal number of electrons gained and lost by the oxidant and reducing agent, multiply by the appropriate coefficient in each of the two half-reactive equations, i.e., 5, 2, and then add them to obtain a balanced ion equation:

4) Write the complete reaction equation:

5k2so3+2kmno4+3h2so4=6k2so4+2mnso4+3h2o

Valence rise and fall method is a method that has a wide range of applications for leveling redox reaction equations. Although the ionic-electronic method is only suitable for the trimming of the ionic equation in solution, it avoids the calculation of valence. The more complex redox reactions carried out in aqueous solutions are generally leveled by the ion-electron method.

These two trimming methods can complement each other.

Example: 2H2O2 = (Mno2) = 2H2O + O2 (arrow) where the valency of H is unchanged What changes is O, O in O2 loses electrons and the valency increases; O in H2O gets electrons, and the valency decreases. So the number of valence atoms is 4.

Trim is based on the change in valency of the elements before and after the reflection. First, if there is a change in valency, the electrons that change before and after are conserved, and then the others are balanced according to the conservation of atoms.

For example, HCL and MNO2 are used to produce Cl2

1 Write the reaction formula HCl+MNO2=(condition)=Cl2+mnCl2+H2O (you can write Cl2 first, and then add it).

2 Find the element of valence Cl loses electrons, then Mn gains electrons and equalizes according to the number of electrons gained.

2hcl2+mno2==cl2+mn2+

3 According to the conservation of atoms, the balance of the atom without valence has H and O, generally produces H2O4HCl+Mno2==Cl2+MnCl2+2H2O, and finally there is a gas precipitated with arrows.

If it's a high school chemistry equation, it depends on how difficult it is, and there are chemical equations in the book that you can memorize special ones, for example, whether the reaction between metal and nitric acid depends on whether it's one to four or three to eight, and then you can memorize a few special parameter calculations, just like the equation for the oxidation of iron hydroxide in the air, and you can memorize the previous one by remembering the factor of four for ferric hydroxide.

It's rare to have no contact poured.

Just use the equation for redox reactions, use the electron transfer and the rise and fall of the valence, use the number of electrons gained and lost to be equal, and the valency rise and fall are equal, or if there are two iron atoms in front of the equation, then add a two in front of the iron atom in front of the next iron atom, and then use the above method.

For the redox reaction, first find out the oxidant reducing agent (or oxidation product reduction product), and then according to the principle of "valence rise and fall conservation", determine the coefficient ratio of the oxidant reducing agent (or oxidation product reduction product), and then obtain the coefficient of the oxidation product reduction product (or oxidant reducing agent), and the rest of the substances are determined according to the conservation of elements.

Use the observation method first, and then gain and lose the conservation of electrons,。。

Number of electrons lost = number of electrons gained.

High school chemistry equation balancing methods and techniques are as follows:

1. Least common multiple method.

Applicable conditions: The matching atom appears only once on the left and right sides of the equation, and this method is suitable for common chemical equations with little difficulty.

2. Odd spouse law.

Applicable conditions: It is applicable to the 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.

3. Establish a law.

Applicable conditions: such as the reaction of most hydrocarbons or compounds containing hydrocarbon and oxygen with oxygen, as well as certain decomposition reactions.

Fourth, the fraction balancing method.

This method can balance chemical reactions with elemental participation in the reaction or elemental generation. Specific steps:

1) first trim the atoms of each element in the compound;

2) equalize the atoms of elemental elements with fractions;

3) Remove the denominator so that the stoichiometric number after trim is an integer.

5. Algebraic method (also known as the method of undetermined coefficients).

Applicable conditions: There are many types of reactants or products, and the trim does not know where to start with the more complex reactions.

6. Observation balancing.

Applicable conditions: Sometimes there will be 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.

There is a law for balancing, but there is no definite law. For the same reaction equation, different methods may be used to balance, and sometimes even several methods may be used at the same time.

High School Chemistry Equation Trim Methods and Skills:

1) Least common multiple method:

In the balancing chemical equation, the elements with a more complex "number" are observed before and after the reaction, and the balancing is carried out first.

First, calculate the least common multiple of the atoms of the element before and after the reaction, use the method of filling in the stoichiometric number before the chemical formula, balance the atom, and then observe the number of atoms of other elements, so that the types of elements and the number of atoms of reactants and products in the chemical reaction are equal.

2) Observational Method:

A method for judging the stoichiometric number of a substance by analyzing the chemical formula of a substance.

3) Odd to even method:

The method of selecting an element with an odd and even number of atoms in the chemical formula before and after the reaction as the starting point of balancing, turning the odd number into an even number, and then leveling the atoms of other elements is called the odd to even method.

4) 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 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.

Trim Tricks for Chemical Equations:

1) Master the essentials of writing chemical formulas:

In the series of chemical terms, the chemical formula is in the position of connecting the previous and the next, and there are element symbols and valency knowledge before it, which is the basis for writing chemical formulas; Then there are chemical equations and ionization equations, etc., which are based on chemical formulas, and if there is an error in the chemical formula, the whole formula is meaningless.

If we use such an erroneous chemical equation as the basis for chemical calculations, we will be even further wrong, and it can really be described as "a small miss, a thousand miles". It can be seen that mastering the essentials of writing chemical formulas directly affects the learning of other chemical terms and other chemical knowledge and skills.

2) Master the skills of writing chemical equations:

In short, when writing chemical equations, they must conform to the objective laws of chemical reactions and cannot be fabricated out of thin air. The writing procedure is generally as follows: write the chemical formula - the coefficient should be balanced - the middle and equal signs - the conditions should be noted - the gas or precipitation should be generated, which should be marked with the arrow number.

To write chemical equations well, it is also necessary to master and use the solubility table of acids, bases, and salts, the order of metal activity and the valency of common elements and atomic groups, as well as the skills of writing chemical formulas of substances.

Equation trim for chemical reactions.

1. 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↑

Note: In the chemical equation of this entry, the ones that are not in bold are the foot markers.

This paragraph] is a collection of poems.

This part of the poem consists of six short poems, the first five introduce you to the five ways of balancing the equation of chemical reactions, and the sixth poem tells you how to use these five methods flexibly and skillfully in the actual balancing process. If you can remember and understand these six little poems, then you can proudly say, "There is not a chemical reaction equation in the world that I will not match ......."”

A simple trim method for the disproportionation reaction.

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.

But too much observation is true, this is just for reference, pay attention to the observation of the drip quickly.