"How to Write Chemical Equations Correctly" Chemical Equations PPT Courseware 8

"How to Write Chemical Equations Correctly" Chemical Equations PPT Courseware 8

A chemical equation is a concise expression of a chemical reaction. It expresses the meaning of a chemical reaction from two aspects: "qualitative" and "quantitative".

(1) The meaning of "quality": It indicates what substances participated in the reaction, what substances were produced, and under what conditions the reaction was carried out.

(2) The meaning of "quantity": From a macroscopic view, it represents the mass ratio between reactants and products. If the reactants are all gases, it can also represent their volume ratio during the reaction. From a microscopic view, the reactants , the particle number ratio of the product.

Example: 2H2+O2=2H2O

The meaning of "quality": upon ignition, hydrogen reacts with oxygen to form water.

The meaning of "quantity": ⑴, from a macroscopic perspective, every 4 parts of mass of hydrogen react with 32 parts of mass of oxygen to produce 36 parts of mass of water, that is, the mass ratio of hydrogen and oxygen when reacting is 1:8, ⑵, from a microscopic perspective See, hydrogen, oxygen and water are all made up of molecules, so this chemical equation also shows that every 2 hydrogen molecules react with 1 oxygen molecule to produce 2 water molecules.

Three ways to read chemical equations

There are three ways to read each equation. Let’s take 2H2O=2H2↑+O2↑ as an example.

(1) Material reading method

The above formula reads "under the condition of electricity, water decomposes to generate hydrogen and oxygen". This kind of

The reading explains the changes in substances during chemical reactions.

(2) Particle reading method

The above formula reads "Under current conditions, every 2 water molecules decompose to generate 2 hydrogen molecules and 1 oxygen molecule." This reading reveals the changes in the structural particles during the chemical reaction and reflects the ratio of the number of particles. relation.

(3) Quantity reading method

The above formula reads "When electricity is applied, 36 parts by mass of water decompose to produce 4 parts by mass of hydrogen and 32 parts by mass of oxygen." This reading shows the quantitative relationship of substances in chemical reactions.

summary:

1. This kind of chemical formula that expresses a chemical reaction is called a chemical equation.

2. The chemical equation shows

(1) Reactants, products and reaction conditions;

(2) Indicates the mass relationship between various substances,

That is, the mass ratio between each substance is determined by relative

expressed by molecular mass (or relative atomic mass)

(3) The quantitative relationship between the particles participating in the reaction

2. Writing principles

1. Based on objective facts

Write down the chemical formulas and reaction conditions of the reactants and products truthfully

2. Comply with the law of conservation of mass

Make the types and numbers of atoms on both sides of the equal sign equal

Chemical equations reflect the objective facts of chemical reactions. Therefore, there are two principles to follow when writing chemical equations:

First, it must be based on objective facts.

Second, we must abide by the law of conservation of mass. The types and numbers of atoms on both sides of the equal sign must be equal.

2. Writing steps

The writing of chemical equations can be summarized as follows: (Take the chemical equation writing of the reaction "potassium chlorate - potassium chloride + oxygen" as an example)

A horizontal line appears on the left and right side

Add a line after trimming

Conditions for betting on equal signs

Arrow marks gas or sediment

Class exercises

1. Balance the following chemical equation:

Fe + O2 = Fe3O4

2. White solid powder potassium chlorate (KClO3) can decompose quickly under manganese dioxide (MnO2) as a catalyst and heating conditions to generate potassium chloride (KCl) and oxygen. Try to write the chemical equation of this reaction.

3. Correctly write the chemical equations for the following reactions

1. Thin wire burning

2. Aluminum foil burning

3. Water is decomposed by electricity

4. Hydrogen peroxide decomposes under the catalysis of manganese dioxide

5. Potassium permanganate decomposes when heated

1. Properties of oxygen:

(1) Reaction between elemental substances and oxygen: (combination reaction)

1. Magnesium burns in air: 2Mg + O2 = ignition = 2MgO

2. Iron burns in oxygen: 3Fe + 2O2 = Ignite = Fe3O4

3. Copper is heated in air: 2Cu + O2 = heating = 2CuO

4. Aluminum burns in air: 4Al + 3O2 = ignition = 2Al2O3

5. Combustion of hydrogen in air: 2H2 + O2 = ignition = 2H2O

6. Red phosphorus burns in air (experiment to study the composition of air): 4P + 5O2 = ignition = 2P2O5

7. Sulfur powder burns in air: S + O2 = Ignition = SO2

8. Carbon is fully burned in oxygen: C + O2 = ignition = CO2

9. Incomplete combustion of carbon in oxygen: 2C + O2 = ignition = 2CO

(2) Reaction of compounds with oxygen:

10. Carbon monoxide burns in oxygen: 2CO + O2 = ignition = 2CO2

11. Methane burns in air: CH4 + 2O2 = ignition = CO2 + 2H2O

12. Alcohol burns in the air: C2H5OH+3O2=ignite=2CO2+3H2O

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