Is there a law to chemical equations, tips and laws for writing chemical equations

Several basic laws of chemical reactions, the law of conservation of mass, the law of conservation of atoms, the law of conservation of energy, these three laws are all introduced in your textbooks, and I won't talk nonsense here.

If you want to learn chemistry well, you just need to master three things: 1 The law of conservation of atoms 2 Valence 3 The periodic table.

Why is the black substance formed by heating the iron wire ferric oxide and not something else? First of all, starting from the law of conservation of atoms, the iron wire is heated in the air, because only oxygen in the air is more active (that is, what you say in the textbook, it can support combustion), so the iron wire can only react with oxygen, that is to say, the elements participating in the reaction are only fe and o, so the resulting substance must only be composed of fe and o, as we all know, fe has two valencies of +2 +3, o is only -2 valence, so the resulting substance has fe2o3 or There are two possibilities So why is the product ferric oxide and not iron oxide Please look at the topic He asked you what is the black substance you produce Here you should pay attention to the word black Only ferric oxide is black and iron oxide is reddish-brown (iron oxide is rust You must have seen it).

There's something called the law of conservation of mass, you know?

The law of conservation of quantities states that in a chemical reaction, the sum of the substances participating in the reaction is equal to the sum of the substances produced after the reaction.

Microscopic explanation: In a chemical reaction, the type, number, and mass of atoms are all unchanged.

Six constants: macroscopic: total mass of matter before and after reaction; the type of element; The quality of the element.

Microscopic: The type of atom does not change; The number of atoms does not change; The mass of the atom does not change.

Two must change:

Macro: A change in the type of matter.

Microscopic: A change in the type of molecule.

One possible change:

Total number of molecules. And then you push it yourself again and it comes out.

Chemistry in middle school is just a matter of reading more books and memorizing chemical formulas. Nothing. As for potassium permanganate, manganese dioxide and potassium manganate are produced and water.

This is because the chemical properties of potassium permanganate are determined, as long as you remember it, the same is true for iron, there are still some days before the high school entrance examination to memorize the chemical formula, I just came here, and the high school entrance examination is also good. Come on. In other words, this has nothing to do with the conservation of mass, personal opinion, don't scold if you don't right.

In junior high school, there were only a few dozen simple chemical equations to memorize.

In high school, you'll learn a unit called redox.

Combined with some knowledge of atomic structure.

It will be known that there is a certain law in the price increase and fall of compounds.

This helps to understand most chemical reactions.

It is also possible to approximate the reaction equation.

But you didn't learn......I can't explain ...... sentence or two

You should work hard first and make progress every day......

Remember, junior high school chemistry is very simple, don't be discouraged, you can definitely do it, everyone is ...... like that

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!

Application of gas symbols: When there is gas in the reactant, the gas symbol is not used in the chemical equation. When there is no gas in the reactant, the gas symbol is used in the chemical equation when the product has gas.

Application of precipitation symbols: When there are substances insoluble in water in the reactants, the precipitation symbol is not used in the chemical equation.

Be sure to pay attention to:

1. There is no gas symbol in the product of the hydrolysis reaction. (The precipitation symbol is not added) 2. The reaction precipitation symbol for the formation of colloids is also not added.

However, if there are gases or insoluble substances in the reflector, there is no need for gassing or precipitation symbols in the product.

Steps to write chemical equations.

For example, to write the chemical equation for the reaction of carbon with iron oxide at high temperatures, the steps are as follows:

Based on the fact of the reaction (which produces iron and carbon dioxide gas), write the chemical formula of the reactant to the left of the equation and the chemical formula of the product to the right of the equation. If there is more than one reactant or product, they are connected separately with a plus sign (the "+" sign between the reactants indicates "......".Follow ......reaction", and the "+" sign between the products indicates "......Follow ......And draw a ** paragraph between the left and right of the formula. In this step, you must pay attention to writing the chemical formulas of various substances correctly, otherwise, the written formulas are meaningless!

According to the law of conservation of mass, the number of atoms of the same element on the left and right sides is equal (i.e., trimming) by the method of matching coefficients, and then the ** segment is changed to an equal sign (the equal sign indicates that "the ...... is generated.""It should be noted that only the appropriate coefficient can be selected for matching, and the chemical formula cannot be changed.

Indicate the reaction conditions, such as ignition, energizing, high temperature, heating (denoted by a " sign), catalyst, etc., on the equal sign or arrow sign, and indicate the state of the gas or precipitate product in the product. The product is a gas, and the right side of its chemical formula is marked with a " " sign (if there is a gas in the reactant, the gaseous product is no longer marked with the " " symbol); The product is precipitated with the addition of the "" sign.

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.

1. Principles for writing chemical equations.

Based on objective facts. Observe the law of conservation of mass.

2. Write the order of chemical equations.

Reactants" "Reaction conditions" "Product" or "Trim" "Changed to ".

Common reaction conditions: ignition, heating ( ) high temperature, catalyst, etc.

Scope of use of """: If there is no gas in the reactant to participate in the reaction, if there is gas in the product, note to the right of the chemical formula of the gaseous substance" "In the reaction carried out in the solution without the participation of solids, if there are solids in the product, note " " to the right of the chemical formula of the solid substance

The total amount of elements is conserved, and a substance can be divided into several elements, such as water, which can be divided into hydrogen and oxygen, for example, this formula since 2H2+O2=2H2O has four hydrogen elements in front, two oxygen elements, and the same four in the back! 2*h2=4h

2*o=2o