All chemical formulas of junior high school chemistry should be balanced and have reaction condition

The trimming methods in junior high school chemistry are:

1. Observation.

For example, NaOH + HCL = NaCl + H2O, in this chemical reaction equation, we only have to observe the number of atoms on the left and right sides of the chemical reaction equation, we can soon find that the number of atoms in the chemical reaction equation is equal, that is, it has been balanced, after we finish writing the chemical reaction equation according to the requirements, we must first observe it to see if the number of atoms on the left and right sides of the chemical reaction equation is equal, if it is not equal, then consider the following methods.

2. Odd spouse numbering method.

Example 2H2O2===2H2O+O2, in this chemical reaction equation, the oxygen atom in the H2O on the right is an odd number, and the oxygen atom in the H2O2 on the left is an even number, so we first add the stoichiometric number 2 on the water surface, so that the hydrogen atom is four, so we should add the metrometric number 2 before H2O2, this method is the most common chemical reaction balancing method in junior high school chemistry, this kind of chemical reaction equation is balanced, first look at the coefficients in the lower right corner of the atoms on both sides, (Keep in mind that the coefficients in the lower right corner of each atom in the chemical formula cannot be changed) to see if there are atoms on both sides, one is odd and the other is even, if so, you can use this method, and the most important thing is to find out whether the oxygen atom has this case.

3. Pending coefficient method.

For example, C2H5OH+3O2===CO2+3H2O, in this chemical reaction equation, we first set the stoichiometric number of C2H5OH as 1, the stoichiometric number 2 can only be added before CO2, the stoichiometric number 3 before H2O, there are 7 oxygen atoms on the right, because C2H5OH provides an oxygen atom, so the oxygen atoms provided by oxygen are only 6, so add the stoichiometric number 3 in front of the oxygen atom, and the chemical equation is balanced. This method is convenient for leveling organic matter (hydrocarbons) when burning to produce carbon dioxide and water. This method is mainly based on the stoichiometric number of organic matter is first set at 1, and then the carbon and hydrogen atoms are leveled, and then the oxygen atoms are leveled.

Fourth, carbon monoxide reacts with iron oxide: 3CO+Fe2O3===2Fe+3CO2

In this chemical reaction equation, we can see that the measurement number of the reducing agent CO is the number of oxygen atoms in the iron oxide, according to this law, this kind of chemical reaction equation can be balanced in this way, for example: 4CO+FE3O4==3FE+4CO2, the stoichiometric number of the reducing agent CO in CO+FEO==FE+CO2 is the same as the number of oxygen atoms in the oxidant, and the stoichiometric number of the oxidant is solved. The stoichiometry of other substances is also easy to solve.

If you can master the above four methods, I believe that you will have no problem writing chemical equations in the high school entrance examination.

The balancing method of the neutralization reaction between the acid and the base is as follows: the coefficient of the hydrogen atom in the acid and the hydroxide ion in the base is the same, that is, how many hydrogen ions are in the acid, how many hydroxide ions are in the base, and at the same time, how many moles of water are generated.

Chemical reactions. Decomposition reaction and displacement reaction, the balancing method is: first the difficult to match the leveling, and finally the elemental.

There is also a metathesis reaction, which can be matched by looking at it.

It's useless for you to memorize equations, you can match them. C2H5OH+3O2===CO2+3H2O This is an example, you can see that the number of Ch O on the left and right sides is the same, and this is the conservation formula that never changes. The number of atoms on either side of the equation remains the same.

You can use fractions when you balance, for example, if you want to equalize, 3 2 times o2 is 3o, if you really understand what I mean by this sentence, then you can match no problem. At this time, the two sides of the equation are balanced, and then the denominator of the fraction is removed, and the two sides of the equation are multiplied by 2, and the 3 2 becomes 3.

The more common one is the least common multiple method, which is to look at the number of atoms and match the least common multiple, which is very easy to master, and you can try to lose a few.

In one point, according to the conservation rate of mass, that is, the type and number of atoms before and after the reaction will not change!

You only need to multiply the coefficients on the left by the number of atoms on the right subscript, which is equal to the product of the coefficients on the right and the number of atoms.

h2o2--h20+02

na+h20--na0h+h2

na202+h20--naoh+02

C+H2SO4 (concentrated)--CO2+SO2+H20

fe(0h)2+02+h20--fe(0h)3

In fact, chemical balancing is not difficult, as long as the valency of each element is marked, and then the rise and fall of the valency before and after the reaction of the same element is listed, and then the total valence of the liter is compared with the total valence of the fall, multiplied by the least common multiple of the two. Take the last one as an example:

Fe:+2--+3 valence liter 1 1*4=+4

0: 0- -2*2=-4 (oxygen has two oxygens, multiply by 2 here) 4*1=-4

That is, the coefficients of Fe(0H)2 and Fe(0H)3 are 4, 02 is 1, and according to the conservation of H, the coefficient of H20 is 2 and substituted into 4Fe(0H)2+02+2H20--4Fe(0H)3

Finally, check according to the conservation of oxygen: reactant 2*4+2+1*2=12 product 3*4=12

1) Observational method.

2) Least common multiple method.

3) Odd spouse method.

You can also make the coefficient of the chemical formula with a large number of atoms 1, and then add others, if there is a fraction, multiply it by the denominator.

The balancing of the chemical equation in junior high school, DU is applied.

Least common multiple method (other methods DAO are specialized in this method.)

deformation). To put it simply, a genus means that on both sides of the equal sign, the number of atoms of each element is equal, and the sum of the atoms of all elements is also equal.

Junior high school chemistry equation balancing, specific operations, can be simplified to:

1. First match the number of atoms of the element with the largest number of atoms on both sides of the equal sign, 2. On the basis of the above, balance the number of atoms of the element with the lowest number at a time, until the least kind of element.

3. Note: The sum of the number of atoms of each element on both sides of the equal sign is: stoichiometric number (chemical formula coefficient) x the number of atoms of the element in this chemical formula (that is, the number in the lower right corner of the element symbol).

4. When leveling the number of atoms of the elements behind the trim, we must pay attention to the stoichiometric number (i.e., coefficient) of the chemical formula of the previous trim, which is the number that already exists, and should not be discarded.

5. Don't leave any kind of element trimmed.

There are several special trimming--- parity (a special method of least common multiples --- junior high school).

The observation method is the simplest method of least common multiples.

Here is only a text explanation for you, and there will be no examples.

Hopefully you can understand because you're smart.

Trim method: copy

1. Least common multiple method.

a. Find out the atoms with a large number of atoms and a single pair on both sides of the reaction formula, and find its least common multiple.

b. Introduce the coefficients of each molecule.

2. Observation.

The stoichiometric number of the chemical formula of each reactant and the chemistry of the product are estimated from a product with a more complex chemical formula.

number of measurements; According to the stoichiometric number of the obtained chemical formula, the stoichiometric number of the other chemical formula is found until the trim.

3. Odd-even matching.

See which element appears most frequently on the left and right sides of the reaction chemical equation; Enter from a chemical formula where the number of elements is an odd number.

hand, which is an even number (i.e., the stoichiometric number is 2); The stoichiometric number obtained from it equalizes the stoichiometric of other chemical formulas.

The number of atoms on both sides is equal.

4. Pending stoichiometric method.

Different unknowns are used to represent the stoichiometric numbers of each chemical formula in the chemical equation; According to the law of conservation of mass, before the reaction.

After the type of each atom remains unchanged and the number of atoms is equal, the system of mathematical equations is listed; Solve a system of equations and make any of them unknown.

The number is 1, find the value of the other unknowns; Finally, the values of the unknowns are substituted into the original chemical equation. 、

Please adopt o( o thank you.

Chemistry equations for junior high school.

The main basis of the formula trim is the law of conservation of mass. i.e. balancing according to the conservation of atoms. This is the capacity of the various atoms on the left, inner and right sides of the equation.

The number of them should be equal. There are some that can be leveled according to parity. That is, if some atoms of the same kind are odd and some are even, multiply by 2 by the least common multiple or odd number