Law Of Conservation Of Mass Worksheet - Free Printable

Let's solve each question on the Law of Conservation of Mass Worksheet step by step. The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction, so:

> Mass of Reactants = Mass of Products

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1. Define the law of conservation of mass.

> The law of conservation of mass states that in a chemical reaction, matter cannot be created or destroyed. The total mass of the substances present before the reaction (reactants) must equal the total mass of the substances after the reaction (products).

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2. According to the LOCO, mass of reactants and products are:

> Equal.

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3. What is the difference between an open system and a closed system?

> - Open System: Matter can enter or leave the system (e.g., an open beaker). Gases may escape, so mass might not appear conserved.
> - Closed System: No matter can enter or leave; only energy can transfer. This ensures mass is conserved because nothing escapes.

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4. Use the LAW OF CONSERVATION OF MASS to fill out the missing information.

We use:
Total Mass of Reactants = Total Mass of Products

Let’s go through each row:

#### A) H₂ + O₂ → H₂O
- Mass of H₂ = 3.4 g
- Mass of O₂ = 10 g
- Total Reactants = 3.4 + 10 = 13.4 g
→ So, Mass of H₂O = 13.4 g

✔ Answer: 13.4 g

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#### B) CH₄ + O₂ → CO₂ + H₂O
- Mass of CH₄ = 12.2 g
- Mass of O₂ = 14 g
- Total Reactants = 12.2 + 14 = 26.2 g
- Mass of CO₂ = 20.0 g
- Let mass of H₂O = x
→ 20.0 + x = 26.2 → x = 6.2 g

✔ Answer: 6.2 g

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#### C) HgO → Hg + O₂
- Mass of HgO = 23.6 g
- Mass of O₂ = 13.0 g
- Let mass of Hg = x
→ x + 13.0 = 23.6 → x = 10.6 g

✔ Answer: 10.6 g

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#### D) Li + O₂ → Li₂O
- Mass of Li = 5.7 g
- Mass of O₂ = ?
- Mass of Li₂O = 24.6 g
→ 5.7 + O₂ = 24.6 → O₂ = 24.6 – 5.7 = 18.9 g

✔ Answer: 18.9 g

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#### E) C₃H₈ + O₂ → CO₂ + H₂O
- Mass of C₃H₈ = 18.9 g
- Mass of O₂ = 11.1 g
- Total Reactants = 18.9 + 11.1 = 30.0 g
- Mass of CO₂ = 15.6 g
- Let mass of H₂O = x
→ 15.6 + x = 30.0 → x = 14.4 g

✔ Answer: 14.4 g

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#### F) Al(OH)₃ → Al₂O₃ + H₂O
- Mass of Al(OH)₃ = 21.8 g
- Mass of Al₂O₃ = 9.7 g
- Let mass of H₂O = x
→ 9.7 + x = 21.8 → x = 12.1 g

✔ Answer: 12.1 g

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#### G) HCl + NaOH → H₂O + NaCl
- Mass of HCl = 2.87 g
- Mass of NaOH = 3.75 g
- Total Reactants = 2.87 + 3.75 = 6.62 g
- Mass of H₂O = ?
- Mass of NaCl = 1.98 g
→ Let mass of H₂O = x
→ x + 1.98 = 6.62 → x = 4.64 g

✔ Answer: 4.64 g

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✔ Final Table Answers:

| Reaction | Reactant(s) | Product(s) |
|--------|-------------|-----------|
| A) | H₂: 3.4 g, O₂: 10 g | H₂O: 13.4 g |
| B) | CH₄: 12.2 g, O₂: 14 g | CO₂: 20.0 g, H₂O: 6.2 g |
| C) | HgO: 23.6 g | Hg: 10.6 g, O₂: 13.0 g |
| D) | Li: 5.7 g, O₂: 18.9 g | Li₂O: 24.6 g |
| E) | C₃H₈: 18.9 g, O₂: 11.1 g | CO₂: 15.6 g, H₂O: 14.4 g |
| F) | Al(OH)₃: 21.8 g | Al₂O₃: 9.7 g, H₂O: 12.1 g |
| G) | HCl: 2.87 g, NaOH: 3.75 g | H₂O: 4.64 g, NaCl: 1.98 g |

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5. Hydrogen & oxygen react to form water. How much water forms if 14.8 g H₂ and 34.8 g O₂ react?

Reaction: H₂ + O₂ → H₂O

- Mass of H₂ = 14.8 g
- Mass of O₂ = 34.8 g
- Total reactants = 14.8 + 34.8 = 49.6 g

By conservation of mass:
→ Mass of water formed = 49.6 g

✔ Answer: 49.6 grams of water

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6. Ammonium nitrate (NH₄NO₃) explodes: NH₄NO₃ → N₂ + O₂ + H₂O

Given:
- 40 g NH₄NO₃ explodes
- Produces 14 g N₂ and 8 g O₂
- Find mass of H₂O formed

Use conservation of mass:
- Mass of reactants = 40 g
- Mass of products = N₂ + O₂ + H₂O
→ 14 g + 8 g + H₂O = 40 g
→ H₂O = 40 – 22 = 18 g

✔ Answer: 18 grams of water

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7. Solid (25 g) mixed with solution (60 g), final mixture = 75 g. Gas released?

- Initial mass = 25 g + 60 g = 85 g
- Final mass of mixture = 75 g
- Difference = 85 – 75 = 10 g

This lost mass is the gas released.

✔ Answer: 10 grams of gas was released

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8. 115 g substance reacts with 84 g of another. What is mass of products?

- Mass of reactants = 115 + 84 = 199 g
- By conservation of mass → mass of products = 199 g

✔ Answer: 199 grams

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9. Student adds 15 g baking soda + 10 g acetic acid → 23 g remaining. Is mass conserved?

- Initial mass = 15 + 10 = 25 g
- Final mass in beaker = 23 g
- Difference = 25 – 23 = 2 g → this is the gas (CO₂) released

So, mass is conserved, but it appears less because the gas escaped.

> ✔ Answer:
> No, mass does NOT appear conserved in the beaker, but it IS conserved overall.
> The gas produced escaped into the air, so it’s not measured in the beaker.
> Therefore, mass is conserved in the universe, but not in the container.

> Is this open or closed?
> → Open system (gas escaped)

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✔ Summary of Answers:

1. Definition: Mass is conserved in chemical reactions.
2. Equal
3. Open system allows matter to escape; closed system does not.
4. Table filled as above.
5. 49.6 g water
6. 18 g water
7. 10 g gas released
8. 199 g products
9. No, mass is not conserved in the beaker due to gas escaping. It is conserved overall. This is an open system.

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