"Law of Conservation of Mass" Source of Life - Water PPT Courseware 2

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"Law of Conservation of Mass" Source of Life - Water PPT Courseware 2

1. Concept of law of conservation of mass

In a chemical reaction, the sum of the masses of the various substances participating in the reaction is equal to the sum of the masses of the substances produced after the reaction.

(1) Coordinate graph of the total mass and time of a substance burning in a closed container.

(2)P 114 Question 8

(1) After the thin iron wire is burned in oxygen, the mass of the product Fe3O4 is equal to the mass of the iron wire participating in the reaction plus the mass of the oxygen participating in the reaction, so the mass of the product is greater than the mass of the thin iron wire.

(2) Because KClO3 is heated under the catalysis of manganese dioxide to generate gas (oxygen) and escapes, the mass of the product is reduced, and the mass of the product oxygen and potassium chloride is equal to the mass of the reactant potassium chlorate, so the mass in the test tube The mass of the remaining substance is less than the mass of the mixture.

Think about it:

Why is the sum of the masses of substances before and after a chemical reaction equal?

Use the molecular and atomic perspectives to explain the reasons for conservation of mass.

Analysis and discussion:

①Did the types of molecules change before and after the chemical reaction?

②Have the types of atoms changed before and after the chemical reaction?

③What is the essence of the chemical reaction process?

2. Reasons for conservation of mass:

Macroscopically: the types of elements remain unchanged before and after the reaction.

Micro:

The types of atoms have not changed.

The number of atoms does not increase or decrease.

Atomic mass does not change.

example:

(1) C2H6O+3O2→2CO2+3

(2) 2AB2+B2 →2AB3

Solution: The elements contained in the reactants: C, H, O,

Number of atoms in the reactants: 2C, 6H, 7O.

Elements contained in the reactants: C, O,

The number of atoms in the product: 2C, 4O.

In chemical changes, according to

The type of elements remains unchanged→the element H with fewer products

The number of atoms does not increase or decrease → there are fewer products: 6H, 3O

3. Law of Conservation of Mass

Six unchanged:

(1) The total mass of reactants and products remains unchanged

(2) The type of elements remains unchanged

(3) The mass of the elements remains unchanged

(4) The types of atoms remain unchanged

(5) The number of atoms remains unchanged

(6) The atomic mass remains unchanged

Two changes:

(1) Change in the type of substance

(2) Changes in molecular types

One possible variation: the total number of molecules.

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Update Time: 2024-07-11

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