"Law of Conservation of Mass" Source of Life - Water PPT Courseware 4

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"Law of Conservation of Mass" Source of Life - Water PPT Courseware 4

learning target:

1. Understand the law of conservation of mass and be able to use it to explain some phenomena in life.

2. Specific application of the law of conservation of mass.

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

Pay attention to observe:

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

2. Changes in the balloon;

3. Changes in quality before and after chemical reactions.

Scheme 2 Determination of the total mass of iron nails before and after the reaction with copper sulfate solution

Experimental phenomenon: Red solid material precipitates on the surface of the iron nail, and the solution changes from blue to light green.

Reaction principle:

Iron + copper sulfate → copper + ferrous sulfate

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

m(Fe)+ m(CuSO4) = m(FeSO4) + m(Cu)

1. Law of conservation of mass

1. Definition

In a chemical reaction, 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 after the reaction.

Formula: A + B = C + D

think about it

Why does the sum of the masses of the substances participating in a chemical reaction equal the sum of the masses of the substances produced by the reaction?

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. Microscopic explanation of conservation of mass:

Before and after a chemical reaction: the type of atom, the mass of the atom, and the number of atoms remain unchanged.

3. Summary

Six constants, two changes, and two possible changes in chemical reactions

Six unchanged

1. The total mass of the substance remains unchanged before and after the reaction;

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. Atomic mass remains unchanged

Both must change

1. Types of substances

2. Types of molecules

Two possible changes: number of molecules, valence of the element

expression and communication

Based on the above experiment, discuss why such experimental results occur.

The reason why such a result occurs is because gas is generated during the reaction.

Summary: If you choose a chemical reaction involving gas participation or gas generation to prove the law of conservation of mass, the reaction must be carried out in a closed container.

【Discussion and exchange】

A classmate discovered in an experiment that after iron rusts, its mass increases; after wood burns, its mass decreases. Based on this, he concluded that there are exceptions to the law of conservation of mass. Do you think this classmate’s inference is correct?

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.

1. Only chemical changes obey the law of conservation of mass. Physical changes do not need to be explained by the law of conservation of mass!

2. Specifically refers to "mass conservation", excluding aspects such as volume.

3. What is conserved is the "total mass", that is, "the total mass of the reactants participating in the reaction" and "the total mass of the products."

Such as precipitation, gas, etc. should be taken into consideration.

"Participate" means that the mass of substances that do not participate in the reaction (remaining) cannot be counted.

2. Application of the law of conservation of mass

1. Determine the types of elements that make up a substance;

1. A certain substance decomposes when heated to produce copper oxide and water. Then all the elements contained in the substance are ()

A. Cu, O B. Cu, O, H C. O.H D. Cu,H

2. According to the experimental facts that water vapor and carbon dioxide are generated after burning candles, it can be inferred that the composition of paraffin (the main component of candles) must contain ()

A. Carbon is an element B. hydrogen an element

C. Two elements, carbon and hydrogen D. Three elements: carbon, hydrogen and oxygen

2. Infer the chemical formula of the reactants or products;

1. According to the law of conservation of mass, it can be seen that in the reaction 2XY+Y2=2Z, the chemical formula of Z is ( )

A. XY2 B. X2Y2 C. X2Y4 D. X2Y

2. According to the reaction 3AB+C2B3=2C+3X, determine the chemical formula of X ( )

A. A2B3 B. A3B2 C. AB2 D. A2B

3. According to the balanced reaction equation 4K2Cr2O7==4 K2CrO4 + 2R + 3O2↑, it can be inferred that the chemical formula of R is ( )

A. CrO B. Cr2O3 C. CrO2 D. CrO3

3. Determine the mass of reactants or products.

1. In the reaction A+B=C+D, it is known that 25gA and 10gB react completely to produce 5gC and mgD, then m is ( )

A. 34g B. 30g C. 6g D. 15 g

2. In a closed container, there are four substances A, B, C, and D. Under certain conditions, they react fully. The mass of each substance before and after the reaction is measured as follows:

Regarding this reaction, which of the following is correct ( )

A. B is the reactant

B． The mass ratio of A and C participating in the reaction is 1:9

C. The basic reaction type of this change is the decomposition reaction

D． The mass of A after reaction is 8g

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Update Time: 2024-07-05

This template belongs to Chemistry courseware Cantonese Education Edition Ninth Grade Chemistry Volume 1 industry PPT template

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