"Simple Calculation Using Chemical Equations" Chemical Equations PPT Courseware 6

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"Simple Calculation Using Chemical Equations" Chemical Equations PPT Courseware 6

learning target

1. Further understand the meaning of chemical equations and perform simple calculations based on correctly writing chemical equations.

2. Master the ideas for calculating chemical equations and standard problem-solving formats.

3. Basic question types related to calculation of chemical equations

What does a chemical equation mean?

(1) Indicates the reactants, products and reaction conditions of chemical reactions;

(2) Express the mass relationship of each substance in a chemical reaction;

(3) Indicates the ratio of the number of particles between reactants and products.

The meaning of chemical equations: Take the reaction of electrolysis of water as an example

1. Indicates that water is energized to generate hydrogen and oxygen.

2. It means that every 36 parts of water by mass react completely to produce 4 parts by mass of hydrogen and 32 parts by mass of oxygen.

3. It means that the number ratio of water molecules, hydrogen molecules and oxygen molecules is 2:2:1.

Explanation: In a chemical reaction, the mass ratio between reactants and products is directly proportional. Therefore, using the direct proportional relationship based on the chemical equation and the known mass of a reactant (or product), the product (reactant) can be found.

The chemical equation expresses the mass relationship of each substance before and after the reaction, that is, the mass ratio between each substance in the reaction is equal to the ratio of the relative molecular (atomic) mass of each substance multiplied by the stoichiometric number.

Hydrogen is the ideal fuel for the cars of the future. 1Kg of hydrogen can power a car with a power of 50KW to run about 100Km.

Water is the source of life. If you find a suitable catalyst, you can use light energy to decompose water to produce hydrogen.

1. Calculate the mass of the product if the mass of the reactants is known.

Example 1: How many grams of oxygen can be obtained by heating and decomposing 6 g of potassium permanganate?

Correct solution steps for calculations based on chemical equations:

[Solution] (1) Assume the unknown quantity (do not bring units)

(2) Write the chemical equation correctly (pay attention to balance)

(3) Write the relative molecular mass, known quantity, and unknown quantity of the relevant substance (write it directly below the corresponding chemical formula. Write the relative molecular mass first. Be sure to multiply the relative molecular mass by the coefficient in front of the chemical formula, and then write the mass. ;The mass unit must be written and unified.)

(4) List the proportional formula and solve it (the calculation results are carried out according to the requirements in the question. If there is no requirement in the question and the division cannot be completed, keep one decimal place)

(5) Write the answer concisely

Notes on calculations based on chemical equations:

1. When setting up an unknown quantity, be sure to pay attention to the mass unit. If the units of the known quantity and the unknown quantity are inconsistent, convert them to the same ones first and then perform the calculation.

2. The chemical equation must be balanced and marked with reaction conditions, gases, and precipitation symbols. Pay attention to the completeness of the chemical equation.

3. The relative molecular mass of related substances is written under the corresponding chemical formula. Be sure to multiply the relative molecular mass by the coefficient before the chemical formula. The known and unknown quantities are written under the corresponding relative molecular mass.

4. The decimal places of the calculation results should be retained according to the requirements in the question. If there is no requirement in the question and an integer cannot be obtained, one decimal place should generally be retained.

Four types of calculations based on chemical equations

1. Find the mass of the product if the mass of the reactants is known.

2. If the mass of the product is known, find the mass of the reactant.

3. If the mass of one reactant is known, find the mass of the other reactant.

4. If the mass of one product is known, find the mass of the other product.

The following errors often occur when calculating chemical equations:

① If you don’t examine the question carefully, you will answer the question incorrectly.

②The element symbol or chemical formula is written incorrectly.

③The chemical equation is written incorrectly or is not balanced.

④The relative molecular mass is calculated incorrectly, resulting in an incorrect mass ratio.

⑤The same substance does not use the same units or the units are not uniform.

⑥The quantity of matter is replaced by the wrong one.

⑦Treat impure things as pure things.

⑧ Substitute the volume of the substance directly into the chemical equation.

3. Calculation of impure reactants or products.

1. In the chemical reaction equation, whether it is a reactant or a product, the mass of the pure substance is substituted. If you encounter impure reactants or products, the impure substance should be converted into the mass of the pure substance.

2. Conversion between the mass of impure substances and pure substances.

Mass of pure substance = Mass of impure substance × Purity (mass fraction)

Exercise: If there are 20 grams of hydrogen and oxygen mixed gas in total, and 2 grams of gas remain after ignition, what is the mass ratio of hydrogen and oxygen in the original mixed gas?

A. 1:4 B. 1:9

C. 4:1 or 1:9 D. 1:4 or 1:9

There are two situations:

One is excessive hydrogen, the mass ratio of hydrogen and oxygen (2+2):16=1:4

The second is excess oxygen, the mass ratio of hydrogen and oxygen 2: (2+16)=1:9

Answer: D

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Update Time: 2024-09-07

This template belongs to Chemistry courseware People's Education Press Ninth Grade Chemistry Volume 1 industry PPT template

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