MindMap Gallery 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.
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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