How to Write Chemical Equations? How to Write Chemical Equations?

Elemental balance, pay attention to conditions, gases, precipitation.

Write the reactants on the left, the reaction conditions on the equal sign, and the products on the right.

Note: 1. If there is no gas in the reactant, but there is gas in the product, draw the "precipitation drawing".

2. Trim.

1. How to write the elemental chemical formula:

First, write the symbols of the elements that make up the elemental matter, and then write the number of atoms that make up a hole and the element molecule in the lower right corner of the element symbol with the number of nanometers. Noble gases are directly composed of atoms and are usually represented by elemental symbols for their chemical formulas. The structure of metal elemental and solid non-metallic elemental is more complex, and it is customary to use elemental symbols to represent their chemical formulas.

2. How to write the chemical formula of the compound:

First, write out all the elemental symbols that make up the compound in the order of positive, first, negative, and second, and then write the number of atoms of that element in each compound molecule with a number in the lower right corner of each element symbol.

A certain order usually refers to: a compound composed of oxygen and another element, and the oxygen symbol is generally written on the right; For compounds composed of hydrogen and another element, the hydrogen symbol should generally be written on the left; For compounds composed of metallic elements, hydrogen elements and non-metallic elements, the non-metallic element symbol should generally be written on the right. The chemical formula of a compound that is directly composed of ions is often expressed as the simplest integer ratio of its ions.

Note: When the ratio of the number of atoms of a constituent element is 1, 1 is omitted and not written; The writing of the chemical formula of oxide generally writes the element symbol of oxygen on the right and the symbol of another element on the left, such as CO2; When writing the chemical formula of a compound composed of metallic elements and non-metallic elements, the metallic element symbol is generally written on the left and the non-metallic element symbol is written on the right, such as NaCl. The sum of positive and negative valency algebra is zero.

The chemical equation is written as follows:To understand the principles of writing chemical equations, it is necessary to be based on objective facts and to observe the law of conservation of mass.

Master the steps of writing chemical equations, taking the thermal decomposition of potassium permanganate as an example.

Write out the chemical formulas of reactants and products, trim chemical equations and check them.

It is sufficient to indicate the conditions under which the chemical reaction occurred and to indicate the state of the product.

How to learn chemistry well?

1. Preview before class and take notes in class.

If we want to learn chemistry well, we must prepare for it before class. It will be more efficient to mark what you don't understand, listen to questions in class, and take good notes in class, which is also conducive to review after class. Note-taking should also be a good way to grasp the key points and difficulties of the teacher.

2. Learn to organize knowledge.

High school chemistry has a lot of knowledge points, and the content is relatively complex, so it is not easy to learn. For this knowledge, we need to process and refine the important knowledge content. We need to discover the rules and organize the messy knowledge more systematically and organized, so that we can grasp and apply the knowledge faster.

For example, find out the similarities and differences of knowledge points, and then summarize them; The same knowledge can be summed together to form a knowledge block; Connected knowledge can be connected to form a knowledge network.

Principles for Writing Chemical Equations:

based on objective facts;

Follow the law of conservation of mass.

Steps to write chemical equations:

Write", "match", "note", "etc.".

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

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

"Scope of use: 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 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" "Example: Red hot iron reacts with water vapor to form ferric tetroxide and hydrogen.

h2o+fe——fe3o4+h2

Obviously, the three iron atoms in Fe3O4 are derived from the iron atoms in the reactants, and the four oxygen atoms in Fe3O4 are derived from the oxygen atoms in the water vapor molecules of the reactants. Therefore, a stoichiometric number 4 must be written before the reactant water vapor chemical formula, and a stoichiometric number 3 must be written before the iron atom

4h2o+3fe——fe3o4+h2

It is not difficult to see that the chemical equation can be balanced by writing a stoichiometric number 4 before the chemical formula of the resulting hydrogen. The reaction conditions are then indicated.

4H2O+3Fe==High Temperature== Fe3O4+4H2 That is, the chemical equation of the observation method is balanced.

If there is hydrogen, hydrogen is used as the standard, and if there is no hydrogen, oxygen is used as the criterion;

The adjustment can only change the coefficient, and the atoms are equalized.

There is no price for hydrogen and oxygen, and it becomes a single and a double balance;

The trim coefficient is now a fraction, and the whole formula is multiplied by 2 and must be flat.

The ionic equation oh h h o.

The process of writing the ion equation:

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

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

Acid salts of strong acids, such as sodium bisulfate, should be divided into sodium ions, hydrogen ions and sulfate ions (only bisulfate belongs to this category in high schools); Weakly acidic acid salts, such as sodium bicarbonate, are split into sodium ions and bicarbonate good slippery zen ions (acid salts such as carbonic acid, phosphoric acid, sulfurous acid, etc. are all of this type).

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

Most of the equations in high school organic chemistry are not difficult, most of them are regular, and they can be written if you compare them more and find common ground.

First, write the chemical formula of the reactant and the product, connect with "+" between the reactants or between the products, connect with "=" between the reactants and the products, and write the reaction conditions above or below the "=", and then balance.

Writing chemical equations should abide by two principles: first, it must be based on objective facts, and it is absolutely impossible to conjecture or fabricate substances and chemical reactions that do not actually exist; Second, to abide by the law of conservation of mass, the types and numbers of atoms on both sides of the equal sign must be equal.

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:

1. According to the fact of the reaction (which produces iron and carbon dioxide gas), write the chemical formula of the reactant on the left side of the equation and the chemical formula of the product on the right side 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.

c+fe2o3──fe+co2

2. 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., trim) by the method of matching coefficient, and then the ** paragraph is changed to an equal sign (the equal sign means 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.

3c+2fe2o3=4fe+3co2

3. Indicate the reaction conditions on and below the equal sign or arrow sign, such as ignition, energization, high temperature, heating (represented by a " sign), catalyst, etc., and at the same time, indicate the state of the gas or precipitated 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.

3c+2fe2o34fe+3co2↑

Notes:

1. The thermochemical equation does not write the reaction conditions, whether it is written correctly, and there is no conclusive conclusion, but it is not written in all the materials of the middle school.

2. The reaction that can be carried out at room temperature and pressure, no need to write conditions; However, if there are specific conditions for the experiments in the questions, they are always marked with specific conditions.

3. When reacting to a single condition, the condition is written above; If there are two or more conditions, what cannot be written above is written below; When there is both a catalyst and other reaction conditions, the catalyst is always written on it.

4. It is a reversible reaction, which is always represented by a two-way arrow.

Na can react with all three hydroxyl groups, NaOH can react with the following two hydroxyl groups, and NaHCO3 can only react with the bottom hydroxyl group.

1. Teaching Objectives.

Knowledge and skills. 1. Analyze and understand the meaning of equations through specific chemical reactions;

2 Understand the writing of chemical formulas.

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 two principles must be observed

It must be based on objective facts.

Follow the law of conservation of mass.

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

Note: Write: According to the experimental facts, write the chemical formula of reactants and products on the left and right sides of the formula, and the catalyst is neither a reactant nor a product.

Matching: The chemical formula is preceded by the appropriate stoichiometric number, and the number of atoms in the chemical formula cannot be changed.

Label: Indicate the reaction conditions and the standard method of and .

Note: Trim methods include: such as observation method, odd spouse method, least common multiple method, universal formula method, etc.

3.Mantra for writing chemical equations:

Reactants are written on the left, and products are written on the right;

Write the chemical formula, and then fill in the coefficient;

**Change the equal sign, don't forget to add conditions;

One. Principles for writing chemical equations.

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.

Two. 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.

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

Three. Precautions when writing chemical equations.

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.If the product of the reaction in solution is solid, note " " " to the right of the chemical formula of the solid substance

Four. Formulas for writing chemical equations Write reactants on the left and products on the right;

First: Observe the elements of the reactants.

Second: observe redox substances.

Third: trim.

Acids and bases, redox, organic matter, etc., all follow the principle of conservation of materials.

Read the textbook well and don't skip the steps so you can't go wrong.