"Law of Conservation of Mass" Quantitative Study of Chemical Reactions PPT Courseware

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"Law of Conservation of Mass" Quantitative Study of Chemical Reactions PPT Courseware

think about it

When a substance undergoes a chemical change, what is the relationship between the sum of the masses of the reactants and the sum of the masses of the products? Chemists have been concerned with this problem since early times.

Scheme 1: Determination of the total mass of red phosphorus before and after combustion

Ignite red phosphorus in a closed container

Pay attention to observe:

1. The phenomenon of red phosphorus burning in the Erlenmeyer flask;

2. Changes in the balloon;

3. Changes in the pallet balance.

Phenomenon:

The burning of red phosphorus produces a large amount of white smoke and releases heat. The balloon first becomes larger and then smaller, but the scale remains balanced.

Text expression: red phosphorus + oxygen → phosphorus pentoxide

Conclusion: The sum of the masses of reactants = the sum of the masses of products

Conservation of mass

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

Only suitable for explaining chemical changes

For example: water cools and forms ice, but the total mass does not change. This shows that this change complies with the law of conservation of mass. Is this statement correct?

No, because this is a physical change that cannot be explained by the law of conservation of mass.

Thinking: If a cover is placed over the burning magnesium bar and all the products are collected and weighed, what will happen?

Summary: In chemical changes involving gas participation or generation, when verifying the law of conservation of mass, it must be done in a closed container.

Law of Conservation of Mass: The sum of the masses of the substances participating in a chemical reaction is equal to the sum of the masses of the substances produced after the reaction.

Several points should be paid attention to when grasping the law of conservation of mass

1. Only applicable to chemical changes, not including physical changes

2. It refers to the conservation of mass, not the conservation of volume or number of molecules.

3. "Total mass" cannot ignore gas and precipitation.

4. The scope of conservation is "substances that participate in the reaction", and substances that do not participate in the reaction cannot be counted.

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.

Think: Reasons for conservation of mass

Types of atoms_______, number of atoms_______.

The mass of an atom _______.

Thinking: Did the molecules change before and after the chemical reaction? Have the elements changed?

Types of molecules_______, types of elements_______.

Types of matter_______.

before and after chemical reaction

It must remain unchanged:

type of atom

number of atoms

mass of atom

Type of element

mass of element

Result: The total mass of the substance remains unchanged

Must change:

(macroscopic) types of matter

(microscopic) types of molecules

Possible changes: number of molecules

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Update Time: 2024-10-02

This template belongs to Chemistry courseware Beijing Curriculum Reform Edition Ninth Grade Chemistry Volume 1 industry PPT template

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