Physical Vs. Chemical Change HW - Angela Peterson | Library ... - Free Printable
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Step-by-step solution for: Physical Vs. Chemical Change HW - Angela Peterson | Library ...
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Step-by-step solution for: Physical Vs. Chemical Change HW - Angela Peterson | Library ...
Let's solve this worksheet step by step, classifying each process as a physical change, chemical change, or both. We’ll use the definitions provided:
- Physical change: The substance changes form, but no new substances are formed. The original substance still exists.
- Chemical change: A new substance is formed, often with energy changes (like heat, light, gas production, color change).
- Both: If a physical change occurs alongside a chemical change.
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- Answer: Physical change
- Explanation: Dissolving is a physical change because NaOH breaks into ions but remains chemically the same. No new substance forms. However, it may release heat (exothermic), but that doesn’t make it a chemical change. So, it's primarily a physical change.
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- Answer: Chemical change
- Explanation: This is a neutralization reaction: HCl + NaOH → NaCl + H₂O. New substances (salt and water) are formed, and heat is released. This is clearly a chemical change.
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- Answer: Physical change
- Explanation: Cutting the sodium pellet only changes its size and shape. The substance is still sodium metal. No new substance is formed.
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- Answer: Physical change
- Explanation: This is a phase change (liquid → gas). The substance is still H₂O. Only the state has changed.
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- Answer: Chemical change
- Explanation: Decomposition means breaking down into simpler substances. KClO₃ → KCl + O₂. New substances are formed. This is a chemical change.
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- Answer: Chemical change
- Explanation: Rusting is oxidation: iron reacts with oxygen and water to form iron oxide (rust). A new substance is formed, so it’s a chemical change.
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- Answer: Physical change
- Explanation: Melting is a phase change from solid to liquid. The substance is still H₂O. So, it’s a physical change.
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- Answer: Chemical change
- Explanation: Limestone (calcium carbonate) reacts with acid (e.g., HCl) to produce CO₂ gas. This is a chemical reaction: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Gas evolution indicates a chemical change.
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- Answer: Chemical change
- Explanation: Souring is due to bacterial action converting lactose to lactic acid. A new substance (lactic acid) is formed, changing taste and properties. This is a chemical change.
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- Answer: Chemical change
- Explanation: Rotting involves decomposition by fungi and bacteria, breaking down cellulose and other compounds into simpler substances. New substances are formed — it’s a chemical change.
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1. Physical change
2. Chemical change
3. Physical change
4. Physical change
5. Chemical change
6. Chemical change
7. Physical change
8. Chemical change
9. Chemical change
10. Chemical change
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- Physical changes: 1, 3, 4, 7
- Chemical changes: 2, 5, 6, 8, 9, 10
No examples here are "both" — although some physical changes (like dissolving) may involve energy changes, they are not considered chemical unless new substances form.
Let me know if you'd like this formatted for printing or submission!
- Physical change: The substance changes form, but no new substances are formed. The original substance still exists.
- Chemical change: A new substance is formed, often with energy changes (like heat, light, gas production, color change).
- Both: If a physical change occurs alongside a chemical change.
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1. Sodium hydroxide dissolves in water.
- Answer: Physical change
- Explanation: Dissolving is a physical change because NaOH breaks into ions but remains chemically the same. No new substance forms. However, it may release heat (exothermic), but that doesn’t make it a chemical change. So, it's primarily a physical change.
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2. Hydrochloric acid reacts with sodium hydroxide to produce a salt, water, and heat.
- Answer: Chemical change
- Explanation: This is a neutralization reaction: HCl + NaOH → NaCl + H₂O. New substances (salt and water) are formed, and heat is released. This is clearly a chemical change.
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3. A pellet of sodium is sliced in two.
- Answer: Physical change
- Explanation: Cutting the sodium pellet only changes its size and shape. The substance is still sodium metal. No new substance is formed.
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4. Water is heated and changed to steam.
- Answer: Physical change
- Explanation: This is a phase change (liquid → gas). The substance is still H₂O. Only the state has changed.
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5. Potassium chlorate decomposes to potassium chloride and oxygen gas.
- Answer: Chemical change
- Explanation: Decomposition means breaking down into simpler substances. KClO₃ → KCl + O₂. New substances are formed. This is a chemical change.
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6. Iron rusts.
- Answer: Chemical change
- Explanation: Rusting is oxidation: iron reacts with oxygen and water to form iron oxide (rust). A new substance is formed, so it’s a chemical change.
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7. Ice melts.
- Answer: Physical change
- Explanation: Melting is a phase change from solid to liquid. The substance is still H₂O. So, it’s a physical change.
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8. Acid on limestone produces carbon dioxide gas.
- Answer: Chemical change
- Explanation: Limestone (calcium carbonate) reacts with acid (e.g., HCl) to produce CO₂ gas. This is a chemical reaction: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Gas evolution indicates a chemical change.
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9. Milk sours.
- Answer: Chemical change
- Explanation: Souring is due to bacterial action converting lactose to lactic acid. A new substance (lactic acid) is formed, changing taste and properties. This is a chemical change.
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10. Wood rots.
- Answer: Chemical change
- Explanation: Rotting involves decomposition by fungi and bacteria, breaking down cellulose and other compounds into simpler substances. New substances are formed — it’s a chemical change.
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✔ Final Answers:
1. Physical change
2. Chemical change
3. Physical change
4. Physical change
5. Chemical change
6. Chemical change
7. Physical change
8. Chemical change
9. Chemical change
10. Chemical change
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Summary:
- Physical changes: 1, 3, 4, 7
- Chemical changes: 2, 5, 6, 8, 9, 10
No examples here are "both" — although some physical changes (like dissolving) may involve energy changes, they are not considered chemical unless new substances form.
Let me know if you'd like this formatted for printing or submission!
Parent Tip: Review the logic above to help your child master the concept of physical vs chemical changes worksheet.
