Equation balancing, to think. The method of equation trimming

mg + hno3 ——mg(no3)2 + nh4no3 + h2o

mg mg2+: 0 valence 2 valence, loss of 2e

hno3 nh3: +5 valence 3 valence, get 8e

So the ratio of Mg2+ to NH4(+) is 4:1

Substitution. 4mg + hno3 ——4 mg(no3)2 + 1 nh4no3 + h2o

Check the consumption of Hno3, which should be 4 2 + 1 + 1 = 10, write the equation:

4mg + 10hno3 ——4 mg(no3)2 + 1 nh4no3 + h2o

Check h, trim water: 10 h on the left, 4+ on the right? 2, the unknown number is 3, substitution;

4mg + 10hno3 ——4 mg(no3)2 + 1 nh4no3 + 3 h2o

Check for oxygen. On the left is 10 3 = 30.

On the right, it is 4 2 3 + 3 + 3 = 30

Trimming!! Remove 1 and change the equal sign.

4mg + 10hno3 == 4 mg(no3)2 + nh4no3 + 3 h2o

The redox method is used for balancing, and the n element and magnesium element are used for the conservation of electron gain and loss.

The equation is wrong, it is impossible to produce ammonium nitrate.

There are several ways to balance equations:

1. Observation method: This method often works for some simple equations. In fact, even if the number is purposefully made up for balancing, there are often factors such as odd and even. This method is likely to work for any kind of equation.

2. Charge Balance Concealer Method: This method is most useful for ion equations. In the ionic equation, except for the insoluble substance macro, gas, and water, the others are written in ionic form, and the charges at both ends of the equation are first equalized, and then the observation method is used to balance water, gas, etc.

This method generally does not miss. But it's too good for redox equations.

3. Redox method: This method is for the redox equation. Remember here: "The valency rises and loses the redox agent". The corresponding is "reducing the valency to obtain a reducing oxidant". The specific usage is:

1) Mark the valency of the element in the upper part of the element where the valency of the element changes, and distinguish whose is higher and whose is lower.

2) Connect the same elements with lines to find and mark the number of higher charges or the number of lower charges.

3) Find the least common multiple and multiply it by the number of charges that increase or decrease, respectively.

4) Trim: Write the least common multiple of each before their respective chemical formulas (i.e., coefficients). And pay attention to whether these elements with valency changes are equal before and after the chemical change, and in general, if they are not equal, they are integer multiples.

5) Cooperate with the observation of the Dharma Yunjing, and balance other things that are really good, such as water, and the insoluble matter generated.

To balance the chemical equation, it is necessary to ensure that the number of atoms in the field is equal in the reactant and the product. Here's how to trim your pants simply:

1.Find out all the reactants and products.

2.Determine the number of atoms of each element in the reactants and products.

3.Find out which elements need to be trimmed.

4.Balance the elements that need to be trimmed by adding coefficients.

5.The cave calls to see if the number of atoms of all the elements in the equation is equal.

For example, balance the following unbalanced chemical equation:

fe + o2 ->fe2o3

The number of Fe atoms in Fe2O3 is 2, the number of O atoms is 3, and the number of O atoms in the reactant is 2, so a coefficient needs to be added to balance the O atom number.

fe + o2 ->2fe2o3

Now the number of Fe and O atoms is balanced. But when checking the equation, you also need to make sure that the atomic numbers of the other elements are also balanced.

Trimming chemical equations requires a certain amount of experience and skill, and for complex reaction equations, more complex methods may be required to trim.

The trimming idea of the chemical equation is that the amount of chemical elements on both sides is equal.

1. We see that there are 3 Fe iron atoms on the right, then Cufes on the left should be equipped with 32, 3 Cufes on the left, 3 Cu copper atoms and 6 S sulfur atoms on the right

3. In the end, only the O oxygen atom remains.

There are 1, 3, and 12 on the right for a total of 16, so the left O should be equipped with 8 <>

Valency changes, electron transfer is more complicated, the method is as follows, please refer to it: Lifting pants.

If the pure book helps, quarrel.

cufes2+o2==cu+feo+fe2o3+so21, first determine the canopy coefficient of the bucket pants with many elements, such as cufes2.

2. Pay attention to the subscript is an even number, such as the subscript of S (sulfur) of cufes2 is 2, and the previous subscript is even, but the subscript of S (sulfur) on the right side of this chemical equation is 1, which can be arbitrarily matched, and the o (oxygen) associated with sulfur is a single term on the left and can be arbitrarily matched.

3. The single element item is placed after the configuration, and the subscript is not 1 first, and the subscript is the last 1.

Specific analysis: FE has 3 on the right, you can try to match 3 in front of CUFES2, then 3 in front of CU on the right, 6 in front of SO2 on the right, at this time Cu, Fe, S have been leveled left and right, only O, a total of 16 O on the right, and pure blocking 8 in front of O2 on the left. The trim is as follows:

3cufes2+8o2==3cu+feo+fe2o3+6so2

Conservation of charge gain and loss, valence rise and fall conservation, conservation of elements and conservation of mass can be used for balance.

First with the easy, then with the hard. Doesn't the school teacher talk about it?

You look for one.

I'll show you how.

First identify some simple small molecules such as H2O and O2, and then come one by one, and you will be conscious after more practice.

2cri3+21cl2+52koh=2k2cro4+6kio3+42kcl+26h2o

Trim according to the rise and fall of the valence. Iodine increases hexavalent and chromium increases by 3, so each chromium triiodide loses 21 electrons and therefore has a stoichiometric ratio of 2:21 to chlorine

For most junior high school children, the most difficult thing in junior high school chemistry is the balancing of equations.

And equations are also a compulsory question in the exam, if the child wants to get a high score, he must be sure to understand the chemistry equation of the fiber early trim method.

So what are the trimming methods for equations?

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 chemical equation of destroying the sparrow that occurs a certain element multiple times, 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 Huiyuan complex;

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.

Under acidic conditions, As2O3 becomes 2ash3 and 3H2O, and the reactants lack H so H+ is supplemented

As2O3+12H+=2ash3+3H2O, according to the conservation of atoms, the coefficient of H+ is 12

AS2O3+12H++12E-=2ash3+3H2O, according to the conservation of charge, the right side is electrically neutral, and there are 12 cations on the left, so add 12 electron trim. This means that 1mol of AS2O3 reacts to give 12mol of electrons. You can see clearly, I did not analyze the valency change of as and h, it was completely obtained by using the conservation of atoms and the conservation of charge.

6zn-12e-=6zn2+, which is the reaction of losing electrons.

Adding up to get the ionic equation, AS2O3+6ZN+12H+=2ash3+6ZN2++3H2O

H+ comes from H2SO4, 12 H+ correspond to 6 H2SO4, and SO42- does not participate in the reaction to the right of the equal sign and happens to combine 6 Zn2+, so the chemical equation is.

as2o3+6zn+6h2o=2ash3+6znso4+3h2o