"How to Write Chemical Equations Correctly" Chemical Equations PPT Courseware 6

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"How to Write Chemical Equations Correctly" Chemical Equations PPT Courseware 6

[Review questions]

1. What is the law of conservation of mass?

The ______ of each substance participating in a chemical reaction is equal to the ______ of each substance produced after the reaction. This law is called the law of conservation of mass.

2. Reasons for conservation of mass in chemical reactions

In all chemical reactions, atomic ______, atomic ______, and atomic ______ before and after the reaction. Therefore, the sum of the masses of the substances participating in the reaction must be equal to the sum of the masses of the substances produced after the reaction.

1. What is a chemical equation?

A formula that uses ______ to represent a chemical reaction is called a chemical equation, also called ______, or ______ for short.

Among them, the substances participating in the reaction do ______. The substances produced after chemical reactions do ______.

2. What does the chemical equation mean?

1. Understanding from a qualitative perspective shows ______, ______ and ______.

2. Understand from a quantitative perspective, indicating the mass relationship of each substance (that is, indicating the ______ ratio between each reactant and product).

3. Understand from a microscopic perspective, showing the ______ relationship between reactants and products.

3. How to read chemical equations:

Take 4P+5O2 = 2P2O5

① Macroscopic reading: Phosphorus and oxygen generate phosphorus pentoxide under ignition conditions

② Microscopic reading: every 4 phosphorus atoms and 5 oxygen molecules generate 2 phosphorus pentoxide molecules under ignition conditions

③Quality reading method: For every 124 parts of phosphorus and 160 parts of oxygen under ignition conditions, 284 parts of phosphorus pentoxide are produced.

There are two principles to follow when writing chemical equations:

One is to write the chemical formulas of _________ and _________ based on _________;

The second is based on _________, the _________ and _________ of various atoms on both sides of the equal sign must be the same.

Example: Write chemical equations for each of the following reactions

1. Sulfur powder burns in the air

2. Magnesium burns in air

3. Iron burns in oxygen

4. Red phosphorus burns in the air

5. Heating a mixture of potassium chlorate and manganese dioxide

6． Heat potassium permanganate

3. How to write chemical equations correctly

1. Principles of writing chemical equations

(1) Based on objective facts,

You cannot invent substances and chemical reactions that do not exist in fact.

(2) Comply with the law of conservation of mass,

To comply with the law of conservation of mass, the number of atoms on both sides of the equal sign must be equal. For writing chemical equations, it is balancing, but it cannot change the chemical formula of the substance.

2. Steps for writing chemical equations

(1) Writing: Write the chemical formulas of the reactants and products based on the facts, connecting them with dashes.

(2) Balance: Balance the chemical equation and check (that is, the number of atoms on both sides of the equal sign must be equal)

(3) etc.: Rewrite the dash as "="

(4) Mark: Mark the reaction conditions and product status “↑” or “↓”

(5) Check: Check whether the chemical formula is written incorrectly, whether the chemical equation is balanced, whether the conditions and material states are marked, and whether they are marked appropriately.

3. Balancing chemical equations

(1) Principles of balancing chemical equations

Balancing a chemical equation is to add appropriate measurement numbers in front of the chemical formula so that the total number of atoms of each element on the left and right sides of the formula (short line) is equal, reflecting the law of conservation of mass. (Cannot change the chemical formula of a substance).

(2) Method of balancing chemical equations

①Observation method

This method is very effective for some simple equations and is balanced by making up the numbers.

②Least common multiple method

The atom with the largest number of atoms before and after the reaction

③Odd-numbered spouse method

Find the key element (it is O): a certain element appears the most before and after the reaction, and the total number of atoms on both sides of the short line is an odd number on one side and an even number on the other.

Reaction conditions and product status

(1) Only one reaction condition is written above the equal sign; if two or more conditions are required, write them separately above and below the equal sign.

(2) Ignition ≠ Heating (△)

Ignite ≠ burn (cannot write burn)

High temperature ≠ heating (△)

(3) When there is gas only in the product (there is no gas in the reactant), mark "↑" on the right side of the chemical formula of the gas substance.

(4) For reactions in solution, only when there is an insoluble solid substance in the product (there is no insoluble solid in the reactant), mark "↓" on the right side of the chemical formula of the solid substance.

Determine whether the chemical equations for the following reactions are written correctly. If not, explain the reasons and correct them.

① Carbon monoxide gas is burned to generate CO2

ignite

2CO+O2 = 2CO2↑

② Use zinc and dilute sulfuric acid to react to produce hydrogen in the laboratory

Zn+H2SO4=ZnSO4+H2

③Mercury oxide decomposes by heat to generate mercury and oxygen

2HgO = 2Hg+O2↑

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Update Time: 2024-10-01

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