"The Rate and Limits of Chemical Reactions" Chemical Reactions and Energy PPT (Lesson 1: The Rate of Chemical Reactions)

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"The Rate and Limits of Chemical Reactions" Chemical Reactions and Energy PPT (Lesson 1: The Rate of Chemical Reactions)

Part 1: Essential knowledge and foundation of literacy

1. The meaning and expression of chemical reaction rate:

【Micro thinking】

(1) In the reaction C(s)+CO2(g) 2CO(g), can C be used to express the rate of the reaction?

Tip: No. The concentration of solid or pure liquid almost does not change before and after the reaction, so it cannot be used to express the rate of chemical reaction.

(2) Can the chemical reaction rate represent the instantaneous rate of a certain reaction?

Tip: The rate of a chemical reaction is the average rate over a period of time, not the instantaneous rate.

2. Factors affecting the rate of chemical reactions:

1. Internal factors: The main factor affecting the rate of chemical reaction is the nature of the reactants themselves.

【Think about it】

When an iron block or an aluminum block of the same shape and size reacts with hydrochloric acid of equal concentration, which one produces hydrogen gas faster?

Tip: Aluminum. The main factor that determines the rate of reaction is the nature of the reactants themselves.

2.External factors:

(1) Experimental research:

①The influence of catalyst:

②Influence of temperature:

③Influence of concentration:

(2) The impact of external factors on speed:

When other conditions remain unchanged, change a certain condition:

【Situation·Thinking】

The ancient royal family's special version of the refrigerator - "Bingjian"

During the Zhou Dynasty, the ancients invented a thing specially used to preserve "ice". In the beginning, the ice pan was only used to preserve ice for the emperor to relieve himself from the heat. Later, a chef in the imperial kitchen discovered that in the north, when it snows in winter, the cold air can make the food last longer. To keep things fresh, ice is also a kind of cold, so we invented the use of ice mirrors to keep things fresh.

(1) What is the principle by which ancient "ice mirrors" and modern refrigerators can preserve food for a longer period of time?

Tip: By lowering the temperature and reducing the rate of chemical reactions, it can extend the storage time of food.

(2) In daily life, using pulverized coal instead of coal and blowing air into the furnace can make the fire more powerful. What is the principle?

Tip: Increase the contact area between coal and air to speed up the reaction rate.

Rate and Limit of Chemical Reaction PPT, Part 2 Content: Key Competencies·Quality Formation

Knowledge point 1: Correct understanding and comparison of chemical reaction rates

[Key points to clarify doubts]

1. Correctly understand chemical reaction rates

2. Comparison method of chemical reaction rates:

(1)Normalization method:

(2) Ratio method:

Compare the ratio of chemical reaction rates to stoichiometric numbers. such as reaction

aA+bB ____ cC, compare the relative sizes of v(A) and v(B): if ______ →v(A)>v(B).

3. Calculation of chemical reaction rate:

(1)Formula method.

v(A)=

(2) "Three-stage" method.

①Write the chemical equation related to the reaction.

② Find out the starting amount, conversion amount, and amount at a certain time of each substance.

【Think·Discussion】

(1) In the reaction of zinc and dilute sulfuric acid to produce hydrogen, which substances can indicate the rate of the reaction?

Tips: sulfuric acid, zinc sulfate. Sulfuric acid and zinc sulfate are dissolved in water, and the concentration can be expressed; zinc is a solid, and the concentration is almost unchanged; because hydrogen leaves the solution, its concentration cannot be expressed.

(2) For the reaction 3A(g)+B(g)====2C(g)+2D(g), under different conditions, the reaction rates represented by A and B are the conditions

①v(A)=0.6 mol·L-1·min-1; condition ②v(B)=0.45 mol·L-1·min-1; then is the rate of this reaction under condition ① faster than the rate under condition ②?

Tip: For the same chemical reaction, when different substances are used to express the reaction rate, the numerical values ​​may be different. Therefore, when comparing the relative magnitude of the reaction rate of the same chemical reaction, the numerical magnitude cannot be directly compared. The numerical values ​​should be converted to the same substance and the same unit first. Then compare the numerical values. The larger the value, the faster the reaction. Converting the rate of condition ① into the rate expressed by B is v(B)=0.2 mol·L-1·min-1, that is, the rate of condition ② is faster than the rate of condition ①.

【Case Demonstration】

[Typical example] (2019·Chengdu High School Testing) In a 1 L closed container, the reaction 4A(s)+3B(g)====2C(g)+D(g) occurred, and after 2 min, the reaction of B The concentration decreases by 0.6 mol·L-1. The correct expression for this reaction rate is ()

A. The reaction rate represented by A is 0.4 mol·L-1·min-1

B. Use B, C, and D to represent the reaction rates respectively. The ratio is 3:2:1.

C. The reaction rate at the end of 2 min, expressed as B, is 0.3 mol·L-1·min-1

D. In these 2 minutes, the value of the rate represented by B gradually decreases, and the value of the rate represented by C gradually increases.

[Question-solving guide] Please pay attention to the following three points when answering this question:

(1) The ratio of chemical reaction rates expressed by different substances for the same reaction is equal to the ratio of stoichiometric numbers.

(2) The chemical reaction rate is the change in concentration of a substance within unit time and belongs to the average rate.

(3) Do not use solids and pure liquids to express reaction rates.

[Analysis] Choose B. A is a solid, and solids are generally not used to express reaction rates, so item A is wrong; in the same reaction, the rates expressed by different substances are proportional to the measurement numbers of each substance in the equation, item B is correct; the reaction rate is the average, not 2 min The final rate, so item C is wrong; in the same time period, the meaning of the rates expressed by reactants and products is the same, and the changing trend is the same, so item D is wrong.

Knowledge point 2 Factors affecting chemical reaction rate

[Key points to clarify doubts]

1.Internal factors:

2.External factors:

When other conditions are equal, change a certain condition:

[Error-prone reminder] (1) The reaction rate slows down due to increasing the concentration of reactants. At this time, the passivation of iron and aluminum in concentrated sulfuric acid and concentrated nitric acid at room temperature should be considered. For example, in the reaction between iron and dilute sulfuric acid to generate hydrogen, if the dilute sulfuric acid is replaced by concentrated sulfuric acid, passivation will occur and the reaction will not proceed.

(2) At the middle school level, we generally only discuss the impact of changing one condition on the rate of chemical reactions when other conditions are the same.

[Knowledge Expansion] The effect of pressure on reaction rate

In a reaction involving gas, the effect of changing the pressure on the reaction rate is essentially to change the volume, which changes the concentration of the reactants.

(1) Compressing the volume or filling in reactants to increase the pressure can speed up the chemical reaction rate.

(2) The volume remains unchanged and gases that do not participate in the reaction are filled. Although the total pressure increases, the concentration of reactants does not change, so the chemical reaction rate remains unchanged.

【Think·Discussion】

(1) H2 is commonly produced in laboratories by reacting about 30% sulfuric acid with a sufficient amount of zinc particles. After the reaction for a period of time, the bubbles become scarce. If some sulfuric acid solution of appropriate concentration is added to the reaction vessel, the bubbles will appear again. What is the reason for the increase again?

Tip: The ionic equation of the reaction is Zn+2H+====Zn2++ H2↑. The size of c(H+) affects the reaction rate of the reaction. The bubbles become rarer because c(H+) decreases and the reaction rate slows down. Add some sulfuric acid solution of appropriate concentration. Since c(H+) in the solution increases rapidly, the reaction rate accelerates and the rate of bubble generation accelerates.

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Update Time: 2024-11-17

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