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Chemical reactions and conservation of mass

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1.What does the law of conservation of mass state?
Easy
- AMass can be created but not destroyed.
- BMass can be destroyed but not created.
- CMass can neither be created nor destroyed.
- DMass can be created and destroyed in chemical reactions.
2.Who is credited with confirming the law of conservation of mass in the late 18th century?
Easy
- AJohn Dalton
- BAntoine Lavoisier
- CDmitri Mendeleev
- DRobert Boyle
3.In a chemical reaction, the total mass of the reactants equals the total mass of the products.
Easy
True or false?
4.In the reaction 2H₂ + O₂ → 2H₂O, if 4 g of hydrogen reacts with 32 g of oxygen, what mass of water is produced?
Medium
- A32 g
- B36 g
- C28 g
- D40 g
5.Match each term on the left with its correct description on the right.
Medium
- Reactant
- Product
- Law of conservation of mass
- Starting substance in a reaction
- Substance formed in a reaction
- Mass is neither created nor destroyed
6.Which of the following is NOT an example of conservation of mass?
Hard
- ABurning wood produces ash and gases that have the same total mass as the original wood and oxygen.
- BIn a closed flask, the mass of reactants equals the mass of products after a reaction.
- CA nuclear fission reaction converts a small amount of mass into energy.
- DDissolving salt in water gives a solution with the same total mass as the salt and water combined.
7.Arrange the following steps in the correct order to demonstrate the law of conservation of mass experimentally:
Medium
- Measure the mass of the products after reaction.
- Mix the reactants in a closed container.
- Measure the mass of the reactants before reaction.
- Compare the masses to confirm they are equal.
8.Which of the following statements about the law of conservation of mass are true? (Select all that apply)
Medium
- AMass can be created in exothermic reactions.
- BThe total mass of reactants equals the total mass of products in a chemical reaction.
- CThe law applies only to closed systems.
- DThe law was first proposed by Albert Einstein.

More questions

9.Arrange the following steps in the correct order to experimentally verify the law of conservation of mass for a reaction between hydrochloric acid and sodium hydroxide.
Medium
- Measure the total mass of the reaction mixture before the reaction.
- Combine the reactants in a closed flask.
- Measure the total mass of the reaction mixture after the reaction.
- Compare the two masses.
10.In a chemical reaction, the total mass of the products is always slightly less than the total mass of the reactants due to energy release.
Easy
True or false?
11.A student burns 2.4 g of magnesium ribbon in air. The product, magnesium oxide, has a mass of 4.0 g. What mass of oxygen from the air combined with the magnesium?
Medium
- A1.6 g
- B2.4 g
- C4.0 g
- D6.4 g
12.In the reaction 2Mg + O₂ → 2MgO, if 6.0 g of magnesium reacts with excess oxygen, what mass of magnesium oxide is produced? (Ar: Mg=24, O=16)
Hard
- A10.0 g
- B8.0 g
- C12.0 g
- D20.0 g
13.Who is credited with experimentally confirming the law of conservation of mass in chemical reactions?
Easy
- AAntoine Lavoisier
- BJohn Dalton
- CDmitri Mendeleev
- DRobert Boyle
14.The law of conservation of mass applies to both chemical and nuclear reactions.
Medium
True or false?
15.A student places 50.0 g of sodium hydrogen carbonate (NaHCO₃) in a sealed container with excess vinegar (acetic acid). After the reaction, the total mass of the container and its contents is measured. Which result is expected?
Medium
- ALess than 50.0 g because gas escapes
- BExactly 50.0 g because the container is sealed
- CMore than 50.0 g because the vinegar adds mass
- DExactly 50.0 g because mass is conserved in all reactions
16.Which of the following statements about the law of conservation of mass are true? (Select all that apply.)
Hard
- AIt applies only to chemical reactions, not physical changes.
- BIt holds exactly in all nuclear reactions.
- CIt is a consequence of atoms being rearranged and not created or destroyed.
- DIt was first clearly formulated by Antoine Lavoisier.
- EIt means the total number of atoms of each element is the same before and after a reaction.
17.When a piece of magnesium is burned in air, the mass of the magnesium oxide produced is greater than the original mass of magnesium because oxygen from the air combines with it.
Easy
True or false?
18.Match each scenario on the left with the correct mass relationship on the right.
Medium
- Burning 12 g of carbon in 32 g of oxygen to form CO₂
- Heating 100 g of calcium carbonate to produce 56 g of calcium oxide
- Dissolving 10 g of salt in 90 g of water
- Total mass after = 100 g
- Total mass after = 44 g
- Total mass after = 44 g of CO₂
19.Place the following steps in the correct order to experimentally verify the law of conservation of mass for the reaction between lead(II) nitrate and potassium iodide solutions.
Hard
- Add potassium iodide solution to the lead(II) nitrate solution and allow the reaction to occur.
- Measure the mass of the two separate solutions before mixing.
- Record the total mass after mixing and compare with the total mass before mixing.
- Place both solutions in separate containers on a balance, then carefully combine them without removing anything.
20.A student performs an experiment to demonstrate conservation of mass. They add 25.0 cm³ of 0.1 M hydrochloric acid to 25.0 cm³ of 0.1 M sodium hydroxide in a sealed flask. The initial total mass is 75.0 g. After reaction, the mass is likely to be:
Medium
- ALess than 75.0 g because gas is produced
- B75.0 g exactly
- CMore than 75.0 g because the reaction releases energy
- DCannot be determined without knowing the products
21.In the reaction 2H₂ + O₂ → 2H₂O, what mass of water is produced when 4.0 g of hydrogen reacts with 32.0 g of oxygen?
Hard
- A28.0 g
- B36.0 g
- C32.0 g
- D4.0 g
22.A student places 5.0 g of sodium hydrogen carbonate (NaHCO₃) in a sealed plastic bag with 10.0 g of vinegar (acetic acid). After the reaction, the mass of the bag and its contents is measured. Which mass is most likely recorded?
Medium
- A15.0 g
- Bless than 15.0 g because gas escapes
- Cmore than 15.0 g because the reaction produces extra matter
- D5.0 g because the vinegar is used up
23.Which of the following are necessary to experimentally demonstrate the law of conservation of mass? (Select all that apply.)
Hard
- AA closed system (no matter can enter or leave)
- BA chemical reaction that produces a gas
- CAccurate measurement of masses before and after reaction
- DUsing a catalyst to speed up the reaction
- EEnsuring all reactants are completely consumed
24.In an open beaker, the mass of the products of a reaction that releases a gas will be less than the mass of the reactants.
Easy
True or false?
25.Match each experimental scenario with the correct mass relationship.
Medium
- Burning magnesium in an open crucible
- Reacting vinegar and baking soda in a sealed bag
- Heating copper carbonate in a sealed tube
- Mass of product (magnesium oxide) > mass of original magnesium
- Mass of bag and contents unchanged
- Mass of tube and contents unchanged
26.Arrange the following steps in the correct order to experimentally verify the law of conservation of mass for the reaction between lead(II) nitrate and potassium iodide solutions.
Medium
- Record the total mass of the flask and contents before reaction.
- Mix the solutions by tilting the flask.
- Place both solutions in a conical flask without mixing.
- Record the total mass after reaction.
- Compare the masses.
27.A student burns 2.4 g of magnesium ribbon in air inside an open crucible. The product, magnesium oxide, has a mass of 4.0 g. What mass of oxygen from the air combined with the magnesium?
Hard
- A1.6 g
- B2.4 g
- C4.0 g
- D6.4 g
28.Which scientist is credited with confirming the law of conservation of mass in the late 18th century?
Easy
- AAntoine Lavoisier
- BJohn Dalton
- CDmitri Mendeleev
- DNiels Bohr
29.The law of conservation of mass states that mass can be created or destroyed in a chemical reaction.
Easy
True or false?
30.When 12 g of carbon reacts with 32 g of oxygen to form carbon dioxide, what mass of carbon dioxide is produced?
Medium
- A44 g
- B40 g
- C36 g
- D48 g
31.Which of the following are true about the law of conservation of mass? (Select all that apply)
Medium
- AIt applies to all chemical reactions.
- BIt was first proposed by John Dalton.
- CIt implies that atoms are rearranged in a reaction.
- DIt means the number of atoms of each element is conserved.
32.Arrange the following steps in the correct order to experimentally verify the law of conservation of mass for a reaction between vinegar and baking soda in a sealed plastic bag.
Medium
- Record the mass of the sealed bag with reactants.
- Mix the reactants by shaking the bag.
- Place baking soda and vinegar in the bag without mixing.
- Record the mass of the bag after the reaction.
33.In an open system, the mass of the products may appear less than the mass of the reactants if a gas is produced and escapes.
Easy
True or false?
34.In the reaction 2Mg + O₂ → 2MgO, if 6.0 g of magnesium reacts with excess oxygen, what mass of magnesium oxide is produced? (Ar: Mg = 24, O = 16)
Hard
- A10.0 g
- B8.0 g
- C12.0 g
- D6.0 g
35.Arrange the following steps in the correct order to experimentally verify the law of conservation of mass for the reaction between lead(II) nitrate and potassium iodide in a sealed container.
Medium
- Record the total mass of the sealed container and contents before reaction
- Mix the solutions by shaking the sealed container
- Record the total mass of the sealed container and contents after reaction
- Place lead(II) nitrate solution and potassium iodide solution in a sealed container without mixing
36.Which of the following are true about the law of conservation of mass? (Select all that apply.)
Hard
- AIt applies to all chemical reactions in closed systems
- BIt was first proposed by Antoine Lavoisier
- CIt states that mass can be created but not destroyed
- DIt is also known as the principle of mass conservation
37.Which of the following scenarios demonstrates the law of conservation of mass?
Hard
- ABurning 2.4 g of magnesium in an open crucible produces 4.0 g of magnesium oxide.
- BHeating 10.0 g of calcium carbonate in an open test tube yields 5.6 g of calcium oxide.
- CReacting 4.0 g of hydrogen with 32.0 g of oxygen in a sealed container produces 36.0 g of water.
- DDissolving 5.0 g of salt in 100.0 g of water produces 105.0 g of salt solution.
38.A student burns 2.4 g of magnesium ribbon in a closed crucible. The product, magnesium oxide, has a mass of 4.0 g. What mass of oxygen from the air combined with the magnesium?
Medium
- A1.6 g
- B2.4 g
- C4.0 g
- D6.4 g
39.In the reaction 2Mg + O₂ → 2MgO, if 6.0 g of magnesium reacts completely with excess oxygen, what mass of magnesium oxide is produced? (Ar: Mg = 24, O = 16)
Hard
- A10.0 g
- B8.0 g
- C12.0 g
- D6.0 g
40.A student adds 5.0 g of baking soda (sodium hydrogen carbonate) to 10.0 g of vinegar (acetic acid) in a sealed plastic bag. After the reaction, the mass of the bag and its contents is 15.0 g. Which statement best explains this result?
Medium
- AThe law of conservation of mass is not valid for this reaction because a gas is produced.
- BThe total mass remains the same because the bag is sealed, preventing any matter from escaping.
- CThe mass increased because the reaction absorbs heat from the surroundings.
- DThe mass decreased because carbon dioxide gas escaped from the bag.
41.Complete the sentence: In a chemical reaction, atoms are rearranged but not created or destroyed. Therefore, the number of atoms of each element is _____.
Medium
In a chemical reaction, atoms are rearranged but not created or destroyed. Therefore, the number of atoms of each element is ____.
42.What is the name of the principle that states mass cannot be created or destroyed in a chemical reaction?
Easy
43.If 10.0 g of calcium carbonate (CaCO₃) is heated and decomposes to produce 5.6 g of calcium oxide (CaO), what mass of carbon dioxide (CO₂) is released?
Hard
44.Complete the sentence:
Easy
According to the law of conservation of mass, the total mass of the ____ must equal the total mass of the ____.
45.If 12 g of carbon reacts completely with 32 g of oxygen to form carbon dioxide, what mass of carbon dioxide is produced?
Medium
46.Iron reacts with sulfur to form iron(II) sulfide: Fe + S → FeS. If 55.8 g of iron reacts completely with 32.1 g of sulfur, what mass of iron(II) sulfide is produced? (Give your answer in grams, to one decimal place.)
Medium
47.Complete the sentence.
Easy
In any chemical reaction, the total mass of the ____ equals the total mass of the ____, provided the system is closed.
48.State the law of conservation of mass in your own words.
Medium
49.When 2.4 g of magnesium is burned in oxygen, 4.0 g of magnesium oxide is produced. What mass of oxygen combined with the magnesium? (Give your answer in grams.)
Hard
50.In the reaction CaCO₃ → CaO + CO₂, if 50.0 g of calcium carbonate decomposes to produce 28.0 g of calcium oxide, what mass of carbon dioxide is produced?
Medium
51.Complete the sentence by filling in the blank.
Easy
In a chemical reaction, atoms are rearranged but not ____.
52.What is the name of the scientist who confirmed the law of conservation of mass in the late 18th century?
Medium
53.Explain why the law of conservation of mass is important for balancing chemical equations.
Medium
54.Describe an experiment you could carry out to demonstrate the law of conservation of mass for a reaction between vinegar and baking soda in a sealed plastic bag.
Medium
55.Explain why the mass of the products in an open beaker reaction may appear less than the mass of the reactants.
Medium
56.Describe an experiment you could carry out to demonstrate the law of conservation of mass for a reaction between vinegar and baking soda in a sealed plastic bag. Include the steps you would take and what you would observe.
Hard
57.If 10.0 g of calcium carbonate (CaCO₃) is heated and decomposes to produce 5.6 g of calcium oxide (CaO), what mass of carbon dioxide (CO₂) is released?
Hard
- A4.4 g
- B3.4 g
- C5.4 g
- D6.4 g
58.If 12 g of carbon reacts completely with 32 g of oxygen to form carbon dioxide, what mass of carbon dioxide is produced?
Medium
- A44 g
- B40 g
- C52 g
- D48 g
59.Iron reacts with sulfur to form iron(II) sulfide: Fe + S → FeS. If 55.8 g of iron reacts completely with 32.1 g of sulfur, what mass of iron(II) sulfide is produced? (Give your answer in grams, to one decimal place.)
Medium
- A105.5 g
- B79.1 g
- C96.7 g
- D87.9 g
60.When 2.4 g of magnesium is burned in oxygen, 4.0 g of magnesium oxide is produced. What mass of oxygen combined with the magnesium? (Give your answer in grams.)
Hard
- A1.6 g
- B0.6 g
- C2.6 g
- D3.6 g
61.In the reaction CaCO₃ → CaO + CO₂, if 50.0 g of calcium carbonate decomposes to produce 28.0 g of calcium oxide, what mass of carbon dioxide is produced?
Medium
- A20 g
- B24 g
- C22 g
- D26 g

Flashcards

What does the law of conservation of mass state?

Mass cannot be created or destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.

Who is credited with confirming the law of conservation of mass?

Antoine Lavoisier in the late 18th century.

In a chemical reaction, what are reactants?

Reactants are the starting substances that undergo change.

In a chemical reaction, what are products?

Products are the new substances formed as a result of the reaction.

What happens to atoms during a chemical reaction?

Atoms are rearranged to form new substances; no atoms are created or destroyed.

How does the law of conservation of mass apply to a closed system?

In a closed system, no matter enters or leaves, so the total mass remains constant.

What is a word equation?

A word equation uses the names of reactants and products to describe a chemical reaction, e.g., hydrogen + oxygen → water.

What is a balanced symbolic equation?

A balanced symbolic equation uses chemical formulas and coefficients to show the same number of each atom on both sides.

Why must chemical equations be balanced?

To satisfy the law of conservation of mass, ensuring the same number of each atom on both sides.

Balance the equation: H₂ + O₂ → H₂O

2H₂ + O₂ → 2H₂O

What is stoichiometry?

Stoichiometry is the calculation of reactants and products in chemical reactions based on conservation of mass.

In the reaction 2Mg + O₂ → 2MgO, if 48 g of Mg reacts, what mass of MgO is produced? (Assume O₂ is in excess)

80 g (since mass is conserved: 48 g Mg + 32 g O₂ = 80 g MgO).

Does the law of conservation of mass hold for nuclear reactions?

No, in nuclear reactions mass can be converted to energy (E=mc²), so mass is not conserved.

What is an open system?

An open system allows matter and energy to enter or leave, so mass may not be conserved.

Give an example of a chemical reaction where mass appears to change but is actually conserved.

Burning wood: the mass of ash is less than the original wood, but the missing mass is in gases (CO₂, H₂O) released.

What is the continuity equation in fluid dynamics?

It expresses conservation of mass: ∂ρ/∂t + ∇·(ρv) = 0, where ρ is density and v is velocity.

In a chemical reaction, if 10 g of calcium carbonate decomposes to produce 5.6 g of calcium oxide, what mass of carbon dioxide is released?

4.4 g (10 g - 5.6 g = 4.4 g CO₂).

What does the coefficient in a balanced equation represent?

The number of molecules or moles of each substance involved in the reaction.

Balance the equation: Fe + O₂ → Fe₂O₃

4Fe + 3O₂ → 2Fe₂O₃

True or false: The law of conservation of mass applies only to chemical reactions.

False. It applies to any closed system in classical mechanics, including physical changes.

What is the difference between a reactant and a product?

Reactants are present before the reaction; products are formed after the reaction.

In the reaction CH₄ + 2O₂ → CO₂ + 2H₂O, identify the reactants and products.

Reactants: CH₄ (methane) and O₂ (oxygen). Products: CO₂ (carbon dioxide) and H₂O (water).

Why is the law of conservation of mass important in chemistry?

It allows us to predict the amounts of reactants and products in a reaction and to balance chemical equations.

What is the mass of 2 moles of water (H₂O)? (Atomic masses: H=1, O=16)

36 g (2 × (2×1 + 16) = 2 × 18 = 36 g).

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