What is the writing law of chemical equations?

1.Displacement reaction (ab+c=a+cb).

Example: Fe + CuSO4 == FeSO4 + Cuzn + 2HCl == ZnCl2 + H2 2Decomposition reaction (c=a+b).

Example: H2CO3 = H2O + CO2

caco3=cao+co2↑

3.Chemical reaction (a+b=c).

Example: H2O + CO2 = H2CO3

3fe+2o2=fe3o4

4.Metathesis reaction (ab+cd=ad+cb).

Example: Na2CO3 + Ca(OH)2=CaCO3 +2NaOH2SO4+2NaOH=Na2SO4+2H2O Method: Least Common Multiples Method, Parity Trim Method, Observation Method.

The reaction between the metal and the acid should first consider whether the acid has oxidation: if there is oxidation, it should be treated as a redox reaction: if there is no oxidation, after judging the reducibility of the cation of the metal and H+, if the reaction can be carried out, the equation will be written.

During the writing process, do not forget the gas symbol and the annotation of the reaction conditions.

As for equation trimming, it can be determined in terms of the valence state in which the metal cation is generated. For example, if the metal cation generated is +3 valence, the coefficient 3 2 can be preceded by h2, and then according to the conservation of atoms before and after the reaction, the coefficient of the substance, and finally the coefficient can be reduced to the simplest integer for a long time. (In the redox reaction, the oxide and the reduction substance have the same number of electrons gained and lost in the reaction, which must be remembered).

There are generally two types of equations, the first type is the one that has appeared in the textbook, and this kind of is generally easier, because you can at least know the product, you only need to determine the coefficient of the valence element according to the gain and loss of electrons, and then the element is conserved in the matching, and even the coefficient will be remembered after you match more in the future, it is basically to write a substance, write a coefficient, if you usually take the exam in this accompaniment leveling also takes more time, it is recommended that you practice the balance (not the observation method of junior high school, but the gain and loss of electrons in my high school to match) This can help you improve the speed and proficiency of redox problems, such as the number of electrons gained and lost by the valence of some common substances O2, Cl2, Febr2, Na2O2, etc., to say that I have never seen the equation, if this exam is not well grasped, it will take a lot of time and difficult to do. In observing whether it is flat or not, if it is uneven, observe the characteristics of the elements. If it's an ionic equation, it's relatively easy to do it, and then look at the left and right charges, and if it's a positive charge, and I'm generating a negative charge, or if the number of positive charges doesn't reach the reactants, you can consider adding h+ oh- (this also depends on the nature of the solution, acidic plus h+ Do not add oh-) and then go to the water if it is a general multi-step reaction (non-redox) this you don't want to write out an equation and merge it (if you really can't do it, you can consider using this method when you want to divide and have time), this is generally speaking, I only determine what the final product is, and then write it down Use the observation method to match, and there is a trick in the matching, you can set a material coefficient as one at will, and then use the elements to keep the horizontal and match other substances to appear fractions.

Finally, you are removing the denominator, and there are some common products, such as Cl2, if you do oxidation, generally, then you will generate Cl- If you are reduced, it is ClO+ If you do both, then both will generate H2O2, reduce a few to generate O2, oxidize to generate H2O, and so on, and many other substances have regularities.

The chemical formula is symbolized with an element.

The combination of and numbers represents the formula of the composition of matter, and the writing law of the chemical formula is positive valence left, negative valence right, and valence.

Marked with the header, the number of atoms, the pair cross, the algebraic sum, is equal to zero.

First, write the element symbols that make up the elemental substance, and then write the number of atoms that make up a elemental molecule in numbers in the lower right corner of the element symbol. Noble gas.

It is directly composed of atoms and is usually represented by an element symbol to represent the chemical formula. The structure of metal elemental and solid non-metallic elemental is more complex, and it is customary to use elemental symbols to represent chemical formulas.

Valency and chemical formula

The chemical formula of the compound is not memorized, it is written according to the valency, so the first thing to remember is to memorize the valency. Then write the chemical formula with valence.

For example, potassium oxide: 1. Write the element symbols in order. Generally, the positive price comes first, and the negative price comes last.

2. Mark the valency of the element above the symbol of the element.

3. Cross the absolute value of the valency of the element, write the pure empty in the lower right corner of another element, as the number of atoms of the element (the offer point that can be reduced), 4. Omit the valency as the chemical formula.

For example: potassium oxide-ko-k o-k2o

Calcium oxide-cao-ca2o2-cao

If the valence is well remembered, there is no need to standardize the valence, and the chemical formula can be written directly according to this method, which is fast and accurate.

For example: potassium oxide-ko-k2o (potassium is +1 valence cross in the lower right corner of o, the number is 1 omitted and not written.) Oxygen is -2 valence and 2 is directly crossed in the lower right corner of k to get the chemical formula. ）

Another example: copper oxide-cuo (copper + 2 valence oxygen-2 valence, can be divisible by 2, the number is 1 omitted and not written,) In this case, you can directly write the chemical formula cuo

For example, alumina-aio-ai2o3 (valence does not need to be written on paper, it is directly used in mind).

In this way, the chemical formula of many compounds can be written, and the valency can be memorized according to the formula, including the valency of the atomic cluster.

Do you understand? If you don't understand, ask me! ok!

Explain a point: valency is not omnipotent, everything has its particularity, for example, sodium peroxide can not be explained with the valence knowledge you have learned now, so learn knowledge to be flexible, to master the general and special laws of things!

Let me explain it to you.

Knowing the reactants and not knowing the products, this is important to improve chemical literacy, and I can summarize it for you succinctly:

1.Judging which chemical reaction the reaction belongs to, the chemical reaction can be divided into, aRedox reactions, b

Precipitation reaction, cNeutralization reaction, DComplexation reaction, e

Addition reaction, fSubstitution reaction, gElimination reaction, h

Polyaddition, IPolycondensation reaction, JPericyclic reaction, k

displacement reactions, and so on.

2.You first have to determine what kind of reaction it belongs to, for example, for example, aluminum and sodium hydroxide reaction, which is the sum of a displacement reaction and a neutralization reaction. First, aluminum reacts with water to form hydrogen and aluminum hydroxide, and then aluminum hydroxide reacts with sodium hydroxide, and the general equation is that aluminum reacts with sodium hydroxide to produce hydrogen and sodium metaaluminate.

3.The balancing equation is based on the conservation of elements, atoms, and electrons gained and lost.

4.The final step is to check that the writing is correct and that the conservation principle is met.

Hope it helps.

If you don't understand, you can ask me.

A detailed description of the chemical formulas of element, oxide, acid, alkali and salt.

First of all, it is necessary to observe two principles: to abide by the law of conservation of mass on the basis of objective facts.

The type and number of atoms on both sides of the equal sign must be equal.

Secondly, the chemical equation.

has its own writing steps (to electrolyze water.

reaction as an example):

Write: According to the objective facts, write the chemical formula of the reactant and the product, and draw a ** between the two sides of the formula; h2o—h2+o2

Matching: Trim the chemical equation so that the number of atoms on both sides of the equal sign is equal, so that it conforms to the law of conservation of mass; 2h2o—2h2+o2

Mark: Indicate the chemical reaction.

conditions (e.g., ignition, heating, catalyst, etc.), change ** to equal sign. If there is no gas in the reactant, the chemical formula of the formed gaseous substance is marked with a " " sign to the right, but if there is also gas in the reactant, the gas generated does not need to use this symbol; If there is a precipitate in the product of the reaction in the solution, the "" sign should be marked to the right of the chemical formula of the precipitated substance; Heating can be used" instead.

Check: check whether the chemical formula is written correctly, check whether the trim is correct, check whether the conditions are marked, and check whether the product status is marked correctly.

For beginners, it is necessary to write chemical equations in strict accordance with the above steps, and the foundation must be solid, and the writing of equations can be completed in one go after proficiency.

To write the equation correctly, it is necessary to take into account the trim problem, and the trim conditions must also be written.