"Chemical Equations" PPT courseware

"Chemical Equations" PPT courseware

Part 1: Think about it

1. Why is the bottom of the Erlenmeyer flask covered with fine sand?

(Prevent the bottom of the Erlenmeyer flask from exploding)

2. What is the function of thin wire?

(ignites white phosphorus)

Conclusion: The sum of the masses of white phosphorus and oxygen participating in the reaction is equal to the mass of phosphorus pentoxide produced.

Sodium hydroxide + copper sulfate = copper hydroxide + sodium sulfate

Conclusion: The sum of the masses of sodium hydroxide and copper sulfate participating in the reaction is equal to the sum of the masses of copper hydroxide and sodium sulfate produced.

Chemical equation PPT, part 2 content: Law of conservation of mass

The sum of the masses of all substances participating in a chemical reaction is equal to the sum of the masses of all substances produced after the reaction.

Notice:

The word "participate"

For example, the reaction of 2 grams of hydrogen and 8 grams of oxygen can produce 10 grams of water, right?

Wrong, only 1 gram of hydrogen participates in the reaction, and only 9 grams of water are produced.

"chemical reaction"

For example, if 1 gram of ice melts into 1 gram of water, does it follow the law of conservation of mass?

No, the law of conservation of mass applies to chemical changes, not physical changes.

practise

Use the law of conservation of mass to explain the following phenomenon:

Iron nails gain mass after they rust

Iron rusts when iron reacts with oxygen in the air, and the product is of course heavier than iron.

1. After the magnesium ribbon is burned in the air, the mass of the product increases compared to the mass of the magnesium ribbon. Why?

2. The mass of coal ash left after coal is burned is less than the mass of coal. Why?

True or False:

1. After potassium permanganate is decomposed by heat, the remaining solid is lighter than the original reactant, which does not comply with the law of conservation of mass. ( )

2. After the candle burns, the remaining solid mass decreases, which does not comply with the law of conservation of mass. ( )

3. When a certain compound is completely decomposed by electricity, it will generate hydrogen (H2) and oxygen (O2). Try to infer that the component elements of this compound must contain ____ elements.

think:

How to use a formula to express a chemical reaction?

For example: carbon burns in oxygen to form carbon dioxide

This formula can indeed express the reactants, products and reaction conditions; however, it is inconvenient to write and is not universally applicable internationally. We have already learned chemical formulas, and we can use chemical formulas to express the composition of substances.

Chemical Equation PPT, Part 3: Chemical Equation

1. The concept of chemical equations

An equation that uses a chemical formula to express a chemical reaction is called a chemical equation.

2. Principles for writing chemical equations:

A. Based on objective facts

B. Follow the law of conservation of mass

3. Steps for writing chemical equations (taking phosphorus burning in oxygen as an example)

1) Based on the reaction facts, write the chemical formulas of the reactants and products on the left and right of the formula, connected with "——".

2) Balance the chemical equation (make the number of atoms before and after the reaction equal)

3) Change the horizontal line to an equal sign

4) Indicate: reaction conditions, product state (gas ↑ or precipitation ↓)

Chemical Equation PPT, Part 4: The Meaning of Chemical Equations

1) Macroscopically, it indicates what substances participate in the reaction and what substances are produced as a result.

Carbon and oxygen react under ignition conditions to produce carbon dioxide.

2) Microscopically, it represents the number ratio of atoms and molecules among various substances.

Particle number ratio: 1:1:1

3) Indicate under what conditions the reaction takes place.

4) Indicates the mass ratio between reactants and products.

Relative molecular mass ratio: 12:32:44

Every 12 parts by mass of carbon reacts with 32 parts by mass of oxygen to produce 44 parts by mass of carbon dioxide.

Chemical Equations PPT, Part 5: Practice:

Balance the following chemical equations

H2 + O2 —— H2O

Na + Cl2 - NaCl

KMnO4 -—— K2MnO4 + MnO2 + O2

Fe2O3 + HCl —— FeCl3 + H2O

Fe2O3 + H2SO4—— Fe2(SO4)3 + H2O

Ca(OH)2 + K2CO3 —— CaCO3 + KOH

Fe2O3 + CO —— Fe + CO2

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