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MindMap Gallery Chemical equations and the law of conservation of mass

Chemical equations and the law of conservation of mass

A summary of the knowledge of chemical equations and the law of conservation of mass in junior high school chemistry, including the application of the law of conservation of mass, the writing steps, reading and meaning of chemical equations, etc.

Edited at 2022-03-31 22:16:49

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Chemical equations and the law of conservation of mass

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Outline

Chemical equations and the law of conservation of mass

Conservation of mass

The essence of chemical reactions

The types of atoms remain unchanged, the number of atoms does not increase or decrease, and the atomic mass does not change

The relationship between various quantities before and after a chemical reaction

Five unchanged

Macro

The type of elements remains unchanged

The total mass of matter remains unchanged

microscopic

The type of atom remains unchanged

The number of atoms remains unchanged

The mass of the atom remains unchanged

two changes

Macro

The type of matter must change

microscopic

The particles that make up matter must change

Two possible changes

The total number of molecules may change

The valency of an element may change

application

Explain the change in mass of a substance before and after a reaction

Determine the mass of reactants or products

Determine the relative molecular mass (or relative atomic mass) of a substance

The sum of the masses of the substances participating in the reaction = the sum of the masses of the substances produced

Determine the elemental composition of a substance

The types of elements remain unchanged before and after the reaction

Determine the chemical formula of reactants or products

The type and number of atoms remain unchanged before and after the reaction

Precautions

The law of conservation of mass can only explain chemical changes but not physical changes

The law of conservation of mass only emphasizes "conservation of mass" and does not include the conservation of the number of molecules, volume, etc.

"Conservation of mass" means that the sum of the masses of the substances participating in the chemical reaction is equal to the sum of the masses of the substances produced, excluding the mass of substances that did not participate in the reaction, and does not include impurities.

chemical equation

writing steps

Writing: Correctly write the chemical formulas of reactants and products

Balance: Balance chemical equations

Note: indicate reaction conditions

Mark: If there is no gas (or solid) in the reactants and there is gas (or solid) in the product after the reaction, then "↑" (or "↓") should be marked on the right side of the chemical formula of the gas (or solid) substance in the product. ). If there is gas (or solid) participating in the reaction, the gas (or solid) generated at this time will not be marked with "↑" (or "↓")

Pronunciation and meaning

" " cannot be read as "plus", but should be read as "and", "and" or "with"

=Cannot read "equal to", should read "generate"

The chemical formula should be read as the name of the substance

Reaction conditions should also be read

① Macro: Water decomposes to generate hydrogen and oxygen under the condition of electricity.

② Microscopically: every 2 water molecules decompose into 2 hydrogen molecules and 1 oxygen molecule under the condition of electricity.

③Quantity: Under electrified conditions, every 36 parts of water by mass decomposes to produce 4 parts by mass of hydrogen and 32 parts by mass of oxygen.

get information

qualitative aspect

What are the reactants and products and the reaction conditions

Quantitative aspect

①Particle number ratio between reactants and products

②The mass ratio between reactants and products

③The sum of the masses of each substance participating in the reaction is equal to the sum of the masses of each substance produced after the reaction.

reaction type of this reaction

reaction type

basic reaction types

Chemical Reaction - Multiple Changes

Decomposition reaction - one becomes many

Displacement reaction - one for one

Metathesis reaction - two for two

Divided from the perspective of oxygen gain and loss

Oxidation reaction - the reaction in which a substance obtains oxygen

Reduction reaction - a reaction in which a substance loses oxygen

Two processes in the same chemical reaction, both must occur at the same time

Divided from an energy perspective

Endothermic reaction - a chemical reaction that absorbs heat

Reactions that require heating or high temperature from start to finish

exothermic reaction - a chemical reaction that releases heat

Combustion of substances, reaction between metals and acids, reaction between quicklime and water

Precautions

Wrong chemical formula of substance

Make up chemical reactions that do not actually exist. For example, if you do not understand the conditions for metathesis reaction to occur, write down some reactions that cannot be carried out.

The chemical equation is not balanced

Wrong mark or omission of "piece" or "↓"

Wrong or missing reaction conditions