How to write chemical equations, how to write chemical equations

1.Write the chemical formula of reactants and products Example: h o - h (negative electrode) + o (positive electrode) (water electrolysis to generate hydrogen and oxygen, reactants written in the front, products written in the back) 2

Trim example: 2h o=2h +o 3Indicate the reaction conditions and state of matter, etc

2h o = energized = 2h + o 4Check that the chemical equation is correct.

1. Element symbols to remember. 2. The chemical formula should be written correctly, and the valency should be remembered if the chemical formula is written correctly.

3. Learn to balance chemical equations.

Note: Valency memory mouth is fast; Monovalent hydrochloride, potassium, sodium, silver, barium oxide, calcium, magnesium, zinc, 246, sulfur, 244, 6, 24, 6, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 6, 2, 2, 2, 6, 2, 2, 2, 6, 2, 2, 6,

The methods of balancing chemical equations are;

1. Least common multiple method, for example: P+O2==P2O5 The least common multiple of 2 and 5 is 10, 10 divided by 2 to get 5 is the coefficient of O2r, and 10 divided by 5 to get 2 is the coefficient.

2. Observation method, for example: Fe+O2 - Fe3O43, set a method, that is, set the coefficient of a substance as one, calculate the other coefficients, if there is a fraction, multiply the denominator with the denominator, remove the denominator. For example, C2H2+O2 - CO2 + H2O 1C2H2 + 5 2O2 - 2CO2 + 1H2O 2C2H2 + 5O2 ===4CO2 + 2H2O

First according to the valency of each element in its compound,,, then according to the conservation of electrons gained and lost.

The first is conservation, the so-called conservation has the conservation of matter, the conservation of electric charge, and the second is to conform to the law of chemical reaction.

Here's how to write a chemical equation:

One. Principles for writing chemical equations.

1.The principles of writing chemical equations must be based on objective facts, and substances and chemical reactions that do not actually exist cannot be invented out of thin air.

2.The law of conservation of mass is observed, so that the types and numbers of atoms on both sides of the equal sign must be equal.

3.Writing steps of chemical equations Writing chemical equations should be carried out according to certain steps to avoid some unnecessary mistakes, such as missing reaction conditions and " ", etc. The general steps in writing a chemical equation can be summarized as:

One writes, two matches, three notes" (taking potassium permanganate thermal decomposition as an example).

Two. Steps for writing chemical equations.

1.Write: Write the chemical formula of the reactant and the product based on the facts, and draw a line between the reactant and the product.

2.Matching: The purpose of the trim chemical equation is to make the types and numbers of atoms on both sides of the equal sign equal, obey the law of conservation of mass, and check it after trimming.

3.Note: Indicate the conditions under which the chemical reaction occurs (ignition, heating, etc.), mark the state of the product (gas, precipitation, etc.), and change ** to equal sign.

4.Check: Check if the chemical equation is correct.

Three. Precautions when writing chemical equations.

1.Common conditions for chemical reactions are "ignition", "heating" (commonly used to indicate "high temperature", "catalyst", etc., written above the equal sign;

2.If there is no gas in the reactant and there is gas in the product, " is added to the right of the chemical formula of the gaseous substance

3.Reaction in solution If the reactant is not solid and the product is solid, note " " to the right of the chemical formula of the solid substance

Sodium bisulfate overdose:

The chemical equation is: 2NaHso + Ba(OH) 2H2O + Na SO + Baso (precipitation).

The ionic equation is: 2H +SO2OH = BASO (precipitation) +2HO

If there is an excess of barium hydroxide:

The chemical equation is: Nahso + BA(OH) = H O + NaOH + BASO (precipitation).

The ionic equation is: H + So Ba oh = H o + Baso (precipitation).

Methods and steps for writing chemical equations:

1. Write the chemical formulas of the reactants and products.

2. Trim chemical equations.

3. Indicate the reaction conditions.

4. Mark the gas symbol (upward arrow) and precipitation symbol (downward arrow).

The symbol of the ion.

Hydrogen ion (H+).

Oxygen ion (O2-).

Fluoride ion (F-).

Sodium ion (Na+).

Magnesium ion (Mg2+).

Sulfur ion (S2-).

Chloride ion (Cl-).

Potassium ion (k+).

Calcium ion (Ca2+).

Iron ion (Fe3+).

ferrous ions (Fe2+), copper ions (Cu2+);

1) N20 valence] (2) no [+2] (3) n2o5 [+5] (4) no2 [+4] (5) hno3 [+5] (6) nh4no3 [-3, +5];

7) The valency of S in NaHSO4 is [+6 valence];

8) The valency of Mn in KMno4 is [+7 valence].

The chemical equation for the preparation of oxygen from manganese dioxide is: 2H2O2=MNO2=2H2O+O2.

There are many methods to prepare oxygen in the laboratory, such as: potassium permanganate oxygen production, hydrogen peroxide (hydrogen peroxide), potassium chlorate decomposition (generally manganese dioxide as a catalyst), sodium peroxide reaction with water, etc.

Equation:. 2kmNO4 (heating) = K2mNO4 + MNO2 + O2 (Note: because the reaction generates MNO2, there is no need to add MX2 as a catalyst) 2KCLO3 (mNO2 heating) = 2KCL+3O2.

Chemistry

Chemistry is a kind of natural science, which studies the composition, properties, structure and change laws of matter at the molecular and atomic levels. The science of creating new matter. The world is composed of matter, and chemistry is one of the main methods and means used by human beings to understand and transform the material world.

It is a discipline with a long and dynamic history, and its achievements are an important symbol of social civilization, and there are two forms of change in chemistry: chemical change and physical change.

The word "chemistry" literally means "the science of change". Chemistry, like physics, is the basic science of the natural sciences. Chemistry is a natural science based on experiments.

qīng hydrogen, hài helium, lǐ lithium, pí beryllium, péng boron. tàn carbon, dàn nitrogen, yǎng oxygen, fú fluorine, nǎi neon, nà sodium, měi magnesium, lǚ aluminum, guī silicon, lín phosphorus, liú sulfur, lǜ chlorine, yà argon, jiǎ potassium, gài calcium.

Helium hài: A gaseous element, colorless and odorless, used to fill light bulbs and neon tubes, and also used to make foam. Liquid helium is often used as a coolant.

Boron péng: Around 200 BC, ancient Egypt, Rome, and Babylon used borax to make glass and weld**. French chemist Guy Lussac used metal potassium to reduce boric acid to produce elemental boron.

Calcium gài: For a long time, chemists considered calcium oxides obtained from the roasting of limestone containing calcium carbonate as an indivisible substance. It is listed in Lavoisier's list of elements published in 1789.

Sulfur: Sulfur is a non-metallic element with the chemical symbol S and atomic number 16. Sulfur is one of the oxygen group elements (group A) and is located in the third period of the periodic table.

Aluminum lǚ: silvery-white light metal. Malleable. When heated in the air, the aluminium powder burns violently and emits a dazzling white flame. Soluble in dilute sulfuric acid, nitric acid, hydrochloric acid, sodium hydroxide and potassium hydroxide solutions, insoluble in water.

Hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxyfluorine, neon, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chloride, argon, potassium, calcium chemical formula: hydrogen (h), helium (he), lithium (li), beryllium (be), boron (b), carbon (c), nitrogen (n), oxygen (o), fluorine (f), neon (ne). Sodium (Na), Magnesium (Mg), Aluminum (Al), Silicon (Si), Phosphorus (P).

Sulfur (S), Chlorine (Cl), Argon (Ar), Potassium (K), Calcium (Ca).

Taking the chemical equation oh h h o as an example, the writing process is as follows:

1. Write the equation first: BA(OH) +2HCl=BACL +2HO.

2. Then disassemble: BA +2OH +2H +2Cl =BA +2Cl +2HO.

3. Remove the same ions on both sides: 2oh +2h = 2h o.

4. Divide both sides by 2 at the same time: oh + h = h o.

Error-prone analysis

1. All oxides and peroxides should be written with chemical formulas, and it must be clear here that active metal oxides or peroxides such as sodium peroxide and sodium oxide are soluble electrolytes but cannot be separated.

2. There are also soluble strong electrolytes like sodium bicarbonate, but sometimes (such as carbon dioxide into saturated sodium carbonate) is also written as a chemical formula, it depends on whether it mainly exists in the form of a solid substance or in the form of ions in solution.

3. Acid salts of strong acids, such as sodium bisulfate, should be split into sodium ions, hydrogen ions and sulfate ions (only bisulfate belongs to this category in high schools); Weakly acid acid salts such as sodium bicarbonate are split into sodium ions and bicarbonate ions (acid salts such as carbonic acid, phosphoric acid, and sulfurous acid belong to this category).

4. Weak electrolytes, non-electrolytes, oxides, elemental substances, precipitation, and gases cannot be disassembled.

1. From the law of conservation of mass, it is not difficult to conclude that the writing of chemical equations must meet the requirements of both "quality" and "quantity", and must abide by the principle of two sails: it must be based on objective facts. Follow the law of conservation of mass.

2. The writing of chemical equations can be summarized in the following three words: writing, matching, and labeling.

3. The written chemical formula must be balanced, and it must be kept in mind that "the type of atoms before and after the reaction remains the same, and the number of atoms does not increase or decrease". Verify whether the number of atoms before and after the reaction is the same, and whether the number of atoms is equal, otherwise it is necessary to check whether the chemical formula is correct or whether the reactants and products increase or decrease at will. Such as:

The equation 2kclo3+mno2 2kcl+3o2 is obviously incorrect, and according to the law of conservation of mass, there is no mn element in the product, thus proving that mno2 cannot be written in the reactant but only in the equal sign. 2kclo3 2kcl+3o2 Keep in mind the above four writing principles, and the writing of chemical equations will not be salty and difficult.

Potassium K+ Calcium Ca2+ Na+ Magnesium Mg2+ Aluminum Al3+

Zinc Ion Zn2+ Iron Ion Fe3+ Ferrous Ion Fe2+ Hydrogen Ion H+ Copper Separation Chain Cu2+

Hg2+ Ag + Barium Ba2+ O2 O2- Cl-

Sulfate ion, SO42- hydrogen, oxygen, oh-chlorate, clo3- nitrate, NO3- carbonate, CO32-

Ammonium NH4+

Note: All plus and minus signs should be written on the top right, here is for the convenience of typing, please understand.