Phản ứng oxi hóa khử: Định nghĩa, phân loại và các dấu hiệu nhận biết

What is redox reaction? What is reducing agent, oxidant? How to identify redox reactions and make their chemical reaction equations? The following article of timhieulichsuquancaugiay.edu.vn will help you answer all the above questions.

What is the definition of redox reaction?

Chemical textbook 8 (Vietnam Education Publishing House) has defined what is redox – reduction reaction.

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Accordingly, “The oxidation – redox reaction is a chemical reaction that occurs at the same time both oxidation and reduction”.

To better understand the concept of redox reactions, we need to clarify the definition of reducing – oxidation and reducing agent – oxidant as well as analyzing the relationship between them.

Reduction – oxidation

In the chemical reaction of iron (III) oxide (Fe2O3) and hydrogen gas (H2) at high temperatures, hydrogen gas will occupy the oxygen element in iron (III) oxide. We have the following reaction equation:

Fe2O3 + 3H2 -> 2Fe + 3H2O

Looking at the above reaction we see that there is a process of separating oxygen atoms from the Fe2O3 compound and we say that there is a Fe2O3 reduction that produces Fe.

In some reactions with different high temperatures, hydrogen gas can also win the oxygen element of some other metals such as copper (II) oxide (CuO), mercury (II) oxide ( MgO), lead (II) oxide (PBO) …

Conclusion: The reduction is a separation of oxygen from the compound.

Oxidation is the effect of oxygen with a substance. For example, with Fe2O3 + 3H2 -> 2Fe + 3H2O reaction, the combination of oxygen atom in Fe2O3 with H2. Conclusion that H2 oxidation forms H2O.

Reducing – oxidant

In iron reaction (III) oxide (Fe2O3) and Hidro gas (H2) above, we can easily see that H2 is an oxygen so it is considered as a reducing agent and Fe2O3 is a yielding oxygen so it is Considered to be oxidized.

Conclusion: In the redox reaction, redox is the oxygen of another substance. Meanwhile, oxidation is a yielding oxygen to other substances.

From these illustrations and definitions, we can draw conclusions for the question “What is redox reaction?”:

“Reduction and oxidation are two opposite processes but occur simultaneously in the same chemical reaction. This chemical reaction is called oxidation – redox reaction ” (Chemical textbook 8, Vietnam Education Publishing House).

A definition of expansion of redox reactions is also associated with electrons. Accordingly: “The oxidation – redox reaction is a chemical reaction, which has an electron change between reaction substances or oxidation – redox reaction is a chemical reaction that has a change in the oxidation number of some elements ”. (Chemical textbook 10, Vietnam Education Publishing House).

How to identify redox reactions

Based on the definition of redox reaction, what above we can easily see what is the sign of redox reaction. Accordingly, the sign to identify a redox reaction is to change the oxidation number of an element.

For example, in the chemical reaction of iron (III) oxide (Fe2O3) and hydrogen producing iron (Fe) and water (H2O), there is a change in oxidation number of H2 and Fe2O3 (H2 which is oxygen; oxygen).

Types of redox reactions

The redox reaction has many different forms such as simple form, molecular reaction, self -oxidation or complex redox reaction.

• Molecular reaction: is the reaction that occurs only in one molecule. Example: 2kclo3 → 2kCl + 3O2

• Self -oxidation reaction: is a chemical reaction in which an increase or decrease of oxidation occurs on just one element. For example: 2Cl2 + 4naoh → 2naCl + 2naClo + 2H2O

• Complex redox reactions: Including chemical reactions with words and reactions that change the oxidation number of more than 2 atoms. For example: Cu2s + HNO3 → Cu (NO3) 2 + CuSO4 + NO + H2O

4 steps to prepare the chemical equation of redox reaction

To make redox reactions, we rely on the extended definition of this reaction. Suppose, in the oxidation – reduction reaction, reducing the electron to oxidize, we can balance the chemical equation of the reaction by the electron balance method. This is a method based on the principle: The total number of electrons due to reducing agents must be equal to the total number of electrons that oxidation receives.

How to make the chemical equation of redox reaction, let's consider the following 4 steps immediately:

• Step 1: Determine the oxidation number of the elements in the reaction to find oxidants and reducing agents.

• Step 2: Write down the oxidation process and reducing the process and then balance each process.

• Step 3: Find the appropriate coefficient for oxidants and reducing agents so that the total number of electrons due to reducing agent is equal to the total number of electrons that oxidation receives.

• Step 4: Put the coefficients of oxidants and reducing agents in the reaction diagram, from which we will calculate the coefficient of other substances present in the chemical equation. Next, check the atomic number of the elements to complete the chemical equation step.

Example: Making equation for iron redox reaction (III) oxide (Fe2O3) and hydrogen (H2) produces iron (Fe) and water (H2O).

• Step 1: Determine the oxidation number of the elements before the reaction of Fe is +3, H is 0; After the Fe reaction is 0 and H is +1.

• Step 2: Write the equation for reduction and oxidation process

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Reducing process:

Fe2O3 + 2.3E -> 2Fe

Oxidation process:

H2 -> H2O + 2.1E

1 Fe2O3 + 2.3E -> 2Fe

3 H2 -> H2O + 2.1E

Fe2O3 + 3H2 → 2Fe + 3H2O

The importance – the significance of redox reaction in life

The redox reaction is an important and popular chemical reaction in nature, affecting many activities in production and life. Reasonable use of redox reactions to increase product efficiency as well as improve their quality.

Some of the most common applications of redox reactions in life are:

• In industry: Application of redox reaction to build many stages in the technological line. For example, aluminum, iron and steel, producing plant protection drugs, fertilizers, pharmaceuticals, cloochric acid …

• In everyday life: Most of the energy people are using is the energy of redox reaction. For example, the fire of charcoal, petrol in the inner combustion engines, the reactions occur in the battery, battery …

In fact, many oxidation – redox reactions take place in the process of metal being destroyed in the wild. However, researchers have also found many measures to limit the redox reactions that are not beneficial.

Redox reactions and applicable exercises

Applying the knowledge of redox reactions that have just been learned to practice solving exercises will help you master and remember knowledge longer. Here are some timhieulichsuquancaugiay.edu.vn exercises collected from 8th and 10th grade chemistry textbooks for readers to refer.

Exercise 1: Choose the correct statements (chemical textbooks 8, Vietnam Education Publishing House)

Copy in the notebook The correct sentences in the following sentences:

A. The oxygen to another is reducing agent.

B. The oxygen yielding substance for other substances is oxidation.

C. The oxygen of other substances is reducing agent.

D. Oxidation – redox reaction is a chemical reaction, including oxidation.

E. Oxidation – redox reaction is a chemical reaction, which occurs at the same time, oxidation and reduction.

Suggestions for answers

The correct statement is the answer: B, C, E.

False statement: A and D because the sentence A misunderstood the nature of reducing and sentence D misunderstood about oxidation – reduction (chemical reactions that occur simultaneously oxidation and reduction, not just oxidation).

Exercise 2: Find the redox reaction and the benefits/ harms of each reaction

Please indicate the following chemical reactions around us, which reaction is oxidation – reduction? Benefits and harms of each reaction? (Chemical textbook 8, Vietnam Education Publishing House).

A. Burning coal in the furnace: C + O2 → CO2.

B. Use carbon oxide reducing iron (III) oxide in metallurgical.

Fe2O3 + 3CO → 2Fe + 3CO2.

C. Calcine lime: CaCO3 → CaO + CO2.

D. iron rust in the air: 4Fe + 3O2 → 2Fe2O3.

Suggestions for the answer:

Oxidation – redox reactions are A, B and D

Analysis of the benefits and harms of each reaction.

• Reaction A: Harm is that produces CO2 polluting the environment. The benefit of the reaction is to produce heat to produce life.

• Reaction B: The benefit of the reaction is iron modulation. The harmful effect of this reaction is to produce CO2 polluting the environment.

• Reaction D: This reaction is only harmful, which is rusty iron, affecting many construction works as well as tools made from iron.

Exercise 3: Exercise No. 5 in textbooks 8, Education Publishing House

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In the laboratory, hydrogen gas is used to eliminate iron (II) oxide and obtain 11.2 g of Fe.

1/ Write the chemical equation of the reaction.

2/ Calculate the volume of iron (III) reacted.

3/ Calculate the volume of consumed hydrogen gas (standard).

Suggestions for the answer:

1/ Write the chemical equation of the reaction: Fe2O3 + 3H2 → 2Fe + 3H2O

2/ Calculate the volume of iron (III) reacted oxide:

Reducing 1 mole of Fe2O3 for 2 moles of Fe.

x = 0.2/2 = 0.1 mol.

m = 0.1 x 160 = 16g.

3/ Reducing 1 mole of Fe2O3 requires 3 mol H2.

So reducing 0.1 mol Fe2O3 requires 0.3 mol H2.

Hidro gas volume: V = 0.3 x 22.4 = 6.72 liters.

Exercise 4: Find redox reactions (Exercise 1, SGK Chemistry 10, Education Publishing House)

A. 2HGO -> 2Hg + O2.

B. CaCO3 -> CaO + CO2.

C. 2Al (OH) 3 -> Al2O3 + 3H2O.

D. 2NAHCO3 -> Na2CO3 + CO2 + H2O.

Which reaction is oxidation – redox reaction.

Suggestions for the answer:

The redox reaction is the answer A

Some exercises on oxidation reaction for students to practice

In addition to the exercises in the chemical textbook, here are some practice exercises for students to practice themselves:

Question 1: For reaction: Na2SO3 + KMnO4 + H2O → Na2SO4 + MNO2 + KOH

The ratio of the coefficient of reducing agent and oxidation after equilibrium is:

A. 4: 3 B. 3: 2 C. 3: 4 D. 2: 3

Question 2 The equilibrium coefficient of FeSO4 and K2CR2O7 respectively:

A. 6; 2 B. 5; 2 C. 6; 1 D. 8; 3

Question 3. The following reaction balance: Fe3O4 + HNO3 → Fe (NO3) 3 + NO + H2O

Question 4. Reaction balance: AS2S3 + HNO3 + H2O → H3ASO4 + NO + H2SO4

Question 5. Calculate the total equilibrium coefficient in the following reaction:

A. 15 B. 14 C. 18 D. 21

Question 6.

CH3CH2OH + K2CR2O7 + H2SO4 → CH3COOH + Cr2 (SO4) 3 + K2SO4 + H2O

Question 7. Determine the equilibrium coefficient of KMnO4 in the following reaction:

SO2 + KMnO4 + H2O → K2SO4 + …

A. 2 B. 5 C. 7 D. 10

Question 8. Balance of oxidation – reduction reaction by balance method E:

a) Fe2O3 + Al → Al2O3 + fenom

b) Fenom + HNO3 → Fe (NO3) 3 + NO + H2O

Question 9: Dissolve 7.8g of Al and Mg powder mixture in excess HCl solution. After reaction, the volume of acid solution increased by 7.0g. The volume of aluminum and magnesium in the first mixture is:

A. 2.7g and 1.2g B. 5.4g and 2.4g C. 5.8g and 3.6g D. 1.2g and 2.4g

Question 10: Give 15.8 grams of KMnO4 with concentrated HCl solution. The volume of chlorine gas obtained under standard conditions is:

A. 5.6 liters. B. 0.56 liters. C. 0.28 liters. D. 2.8 liters.

Above is the general information of timhieulichsuquancaugiay.edu.vn about redox reactions redox under the 8 and 10 chemistry program. Do not forget to read the timhieulichsuquancaugiay.edu.vn website every day to find more interesting basic knowledge surrounding subjects. Learn!

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