homework: physical and chemical changes
decide if the following are physical or chemical changes (write physical or chemical in the blank.)
iron rusting: fe₍ₛ₎ + o₂₍₉₎ ⟶ fe₂o₃₍ₛ₎
condensation of water: h₂o₍₉₎ ⟶ h₂o₍ₗ₎
combustion of methane: ch₄₍ₛ₎ + o₂₍₉₎ ⟶ co₂₍₉₎ + h₂o ₍ₗ₎
sublimation of carbon dioxide: co₂₍ₛ₎ ⟶ co₂₍₉₎
salt dissolves in water: nacl₍ₛ₎ stackrel{h₂o}{⟶} nacl₍ₐq₎
rubbing alcohol evaporating: c₃h₇oh₍ₗ₎ ⟶ c₃h₇oh₍₉₎
corrosion of zinc: zn₍ₛ₎ + hcl₍ₐq₎ ⟶ zncl₂₍ₐq₎ + h₂₍₉₎
ice formation: h₂o₍ₗ₎ ⟶ h₂o₍₉₎
hexane burning: c₆h₁₄₍ₗ₎ + o₂₍₉₎ ⟶ co₂₍₉₎ + h₂o ₍ₗ₎
gold melting: au₍ₛ₎ ⟶ au₍ₗ₎
combustion of hydrogen gas: h₂₍₉₎ + o₂₍₉₎ ⟶ h₂o ₍ₗ₎
photosynthesis in plants: co₂₍₉₎ + h₂o ₍ₗ₎ ⟶ c₆h₁₂o₆₍ₛ₎ + o₂₍₉₎
glucose being dissolved: c₆h₁₂o₆₍ₛ₎ stackrel{h₂o}{⟶} c₆h₁₂o₆₍ₐq₎
decomposition of hydrogen peroxide: h₂o₂₍ₗ₎ ⟶ h₂o₍ₗ₎ + o₂₍₉₎

Question

Accepted Answer

To solve this, we determine if a change is physical (no new substance, just state/shape change) or chemical (new substance formed, often with a reaction equation).

### 1. Iron rusting: $\ce{Fe_{(s)} + O_{2(g)} -> Fe_{2}O_{3(s)}}$
A new substance ($\ce{Fe_{2}O_{3}}$) is formed.
Answer: chemical

### 2. Condensation of water: $\ce{H_{2}O_{(g)} -> H_{2}O_{(l)}}$
Only state (gas to liquid) changes, no new substance.
Answer: physical

### 3. Combustion of methane: $\ce{CH_{4(s)} + O_{2(g)} -> CO_{2(g)} + H_{2}O_{(l)}}$
New substances ($\ce{CO_{2}}$, $\ce{H_{2}O}$) are formed.
Answer: chemical

### 4. Sublimation of carbon dioxide: $\ce{CO_{2(s)} -> CO_{2(g)}}$
Only state (solid to gas) changes, no new substance.
Answer: physical

### 5. Salt dissolves in water: $\ce{NaCl_{(s)} ->[H_{2}O] NaCl_{(aq)}}$
$\ce{NaCl}$ dissolves, no new substance (still $\ce{NaCl}$, just aqueous).
Answer: physical

### 6. Rubbing alcohol evaporating: $\ce{C_{3}H_{7}OH_{(l)} -> C_{3}H_{7}OH_{(g)}}$
Only state (liquid to gas) changes, no new substance.
Answer: physical

### 7. Corrosion of zinc: $\ce{Zn_{(s)} + HCl_{(aq)} -> ZnCl_{2(aq)} + H_{2(g)}}$
New substances ($\ce{ZnCl_{2}}$, $\ce{H_{2}}$) are formed.
Answer: chemical

### 8. Ice formation: $\ce{H_{2}O_{(l)} -> H_{2}O_{(s)}}$ (Note: The original has a typo, should be $\ce{H_{2}O_{(l)} -> H_{2}O_{(s)}}$ for ice). Only state (liquid to solid) changes, no new substance.
Answer: physical

### 9. Hexane burning: $\ce{C_{6}H_{14(l)} + O_{2(g)} -> CO_{2(g)} + H_{2}O_{(l)}}$
New substances ($\ce{CO_{2}}$, $\ce{H_{2}O}$) are formed.
Answer: chemical

### 10. Gold melting: $\ce{Au_{(s)} -> Au_{(l)}}$
Only state (solid to liquid) changes, no new substance.
Answer: physical

### 11. Combustion of hydrogen gas: $\ce{H_{2(g)} + O_{2(g)} -> H_{2}O_{(l)}}$
New substance ($\ce{H_{2}O}$) is formed.
Answer: chemical

### 12. Photosynthesis in plants: $\ce{CO_{2(g)} + H_{2}O_{(l)} -> C_{6}H_{12}O_{6(s)} + O_{2(g)}}$
New substance ($\ce{C_{6}H_{12}O_{6}}$) is formed.
Answer: chemical

### 13. Glucose being dissolved: $\ce{C_{6}H_{12}O_{6(s)} ->[H_{2}O] C_{6}H_{12}O_{6(aq)}}$
$\ce{C_{6}H_{12}O_{6}}$ dissolves, no new substance (still glucose, aqueous).
Answer: physical

### 14. Decomposition of hydrogen peroxide: $\ce{H_{2}O_{2(l)} -> H_{2}O_{(l)} + O_{2(g)}}$
New substances ($\ce{H_{2}O}$, $\ce{O_{2}}$) are formed.
Answer: chemical

### Final Answers (in order):
1. chemical
2. physical
3. chemical
4. physical
5. physical
6. physical
7. chemical
8. physical
9. chemical
10. physical
11. chemical
12. chemical
13. physical
14. chemical

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QUESTION IMAGE

Question

Explanation:

1. Iron rusting: $\ce{Fe_{(s)} + O_{2(g)} -> Fe_{2}O_{3(s)}}$

Answer:

2. Condensation of water: $\ce{H_{2}O_{(g)} -> H_{2}O_{(l)}}$