Chemistry 8 Lesson 17: Exercise 3
1. Summary of theory
1.1. Chemical Phenomena
A chemical change is a change in which one substance produces another substance.
– Chemical reaction is the process of changing from one substance to another.
The initial substance that is changed in a reaction is called the reactant or the reactant.
New substances formed in a reaction are called products.
In chemical reactions, only the bonds between atoms change, causing one molecule to change into another.
1.2. Chemical equation
Chemical equations are used to briefly represent chemical reactions. Includes chemical formulas and appropriate coefficients of the reactants and constituents.
Steps to create a chemical equation:
Step 1: Write a reaction diagram showing the chemical formulas of the reactants and products.
Step 2: Balance the number of atoms of the elements present in the reaction: Find the appropriate coefficients in front of the formulas.
Step 3: Write a chemical equation.
2. Illustrated exercise
2.1. Form 1: Write a word equation
Write word equations for the following reactions:
a) Burning a candle made of paraffin produces carbon dioxide and water vapor.
b) Nitrogen gas reacts with hydrogen gas to form ammonia.
c) When overheated, the fat burns and decomposes into carbon and steam.
d) Burning limestone containing calcium carbonate to form quicklime is calcium oxide with steam.
a) Prafin + oxygen gas → carbon dioxide + water vapor
b) Nitrogen gas + hydrogen gas → ammonia
c) Fat → carbon + steam
d) Calcium carbonate → calcium oxide + steam
2.2. Type 2: Signs of a chemical reaction
Identify the following chemical reactions:
a) Heating potassium permanganate potassium permanganate (purple) after a while turns black as manganese dioxide.
b) Blowing into a clear lime water solution containing calcium hydroxide, a white board of calcium carbonate will appear on the surface.
c) When the potash is put into the blue ink bottle containing copper sulfate, the color of the ink bottle fades to transparent and solids settle to the bottom of the bottle.
d) The candle is burning, the candle is getting shorter and shorter.
e) A comet is a planet that, when it moves, brings along countless cosmic dust particles. As they approach the Sun, these dust particles burn, glow, and this light is visible from Earth.
a) Signs: from purple to black.
b) Signs: white board appears.
c) Signs: green → transparent, with solids settling.
d) Sign: shortened shape.
e) Signs: burning, glowing.
2.3. Form 3: Make a chemical equation
Give a diagram of the following reactions:
a) Na + O2 → Na2O
b) P2O5 + FRIENDS2O → HOW3PO4
c) HgO → Hg + O2
d) Fe(OH)3 → Fe2O3 + FRIENDS2O
Prepare a mathematical equation and give the ratio of the number of atoms and molecules of the substances in each reaction.
a) 4Na + O2 → 2Na2O
Ratio: number of Na atoms: number of O . molecules2: number of Na . molecules2O = 4 : 1 : 2.
b) P2O5 + 3 HOURS2O → 2H3PO4
Ratio: Number of P . molecules2O5 : number of molecules H2O: number of molecules H3PO4 = 1 : 3 : 2.
c) 2HgO → 2Hg + O2
Ratio: number of molecules of HgO: number of atoms of Hg: number of molecules of O2 = 2 : 2 : 1.
d) 2Fe(OH)3 → Fe2O3 + 3 HOURS2O
Ratio: number of molecules of Fe(OH)3 : number of Fe . molecules2O3 : number of molecules H2O = 2 : 1 : 3.
2.4. Form 4: Conservation of mass exercise
For 3 g of iron to burn in air, 5.04 iron(II) oxide is produced. Calculate m of oxygen
Applying the law of conservation of mass has
mFe + mO = mFeO
3 + m = 5.04
⇔ m = 2.04 (g)
3.1. Essay exercises
Question 1: Write a chemical equation for the reaction of iron metal with a dilute solution of sulfuric acid given that the product is iron(II) sulfide and a gas is released?
Verse 2: Reacting iron with hydrochloric acid yields 3.9 g of iron salts and 7.2 g of levitation gas. Total mass of reactants?
Question 3: Calculate the mass of quicklime knowing 12 g of limestone and the appearance of 2.24 l of hydrogen gas?
Verse 4: Add sodium metal (Na) to chlorine gas (Cl2). What is the formed product?
Question 5: Explain the phenomenon of food going rancid for a long time?
3.2. Multiple choice exercises
Question 1: Choose the appropriate coefficient and chemical formula of the missing substance
CuO + ? HCl → CuCl2 + ?
A. THEY2O and 1:2:1:1
B. FAMILY2 and 1:1:1:1
C. FAMILY2O and 1:2:1:2
D. O2 and 1:1:1:1
Verse 2: Choose the correct answer
In a chemical reaction, which microparticle is conserved?
A. Molecular Particles
B. Atomic Particles
C. Both nuts
D. There are no seeds
Question 3: Choose the correct equation for nitrogen and hydrogen gas
A. WOMEN2 + 3 HOURS2 → SMALL3
B. WOMEN2 + FRIENDS2 → SMALL3
CN2 + 3 HOURS2 → 2 SMALL3
D. WOMEN2 + FRIENDS2 → 2 SMALL3
Verse 4: To preserve Na in the laboratory, how do people use?
A. Soak in water
B. Soak in alcohol
C. Soak in kerosene
D. Put in a sealed jar
Question 5: The coefficient of Al in the following reaction is
Al + HIM2SO4 → Al2(SO)4)3 + FRIENDS2
After the lesson to know:
- Ability to distinguish between chemical and physical phenomena
- Write chemical equations knowing the reactants and products.