Worksheet titled "Exothermic vs Endothermic Reactions Worksheet" with handwritten notes and corrections, illustrating examples of exothermic and endothermic processes.

Let's go through the Exothermic vs Endothermic Reactions Worksheet and correct any mistakes, then provide a clear explanation for each process. The goal is to correctly identify whether each process is exothermic (Exo) or endothermic (Endo) based on energy flow.

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🔍 Key Definitions:

- Exothermic (Exo): Energy is released by the system to the surroundings.
- Endothermic (Endo): Energy is absorbed by the system from the surroundings.

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We'll evaluate each row:

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#### 1. An ice cube melts after being left out on the table
- System: Ice cube
- ✔ Endo (✔️ Correct)
- ✘ Incorrectly marked as Exo in the worksheet (but it's actually Endo)

> Explanation: Melting requires heat to break bonds in solid ice → energy absorbed from surroundings (table/air). So, endothermic.

✔ Correct Answer:
| Process | System | Exo | Endo | Explanation |
|--------|--------|-----|------|-------------|
| 1. Ice melting | ice cube | | ✔ | Heat is absorbed from surroundings to melt ice |

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#### 2. Cooking an egg in a frying pan
- System: Egg
- ✔ Endo (✔️ Correct)
- ✔️ Marked correctly

> Explanation: Egg absorbs heat from the pan to cook → energy absorbed → endothermic.

✔ Correct

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#### 3. Burning a match
- System: Match
- ✔ Exo (✔️ Correct)
- ✔️ Marked correctly

> Explanation: Combustion releases heat and light → energy released → exothermic.

✔ Correct

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#### 4. Human body using energy from food digestion
- System: Food
- ✔ Exo (✔️ Correct)
- ✔️ Marked correctly

> Explanation: Digestion breaks down food molecules, releasing energy (ATP) → energy released → exothermic.

✔ Correct

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#### 5. Morning dew forming on grass & plants
- System: Dew
- ✘ Incorrectly marked as Exo
- Should be: Exo? Let’s analyze...

> Dew forms when water vapor condenses into liquid. Condensation releases heat → exothermic process.

But here’s the catch: The system is "dew" — meaning the liquid water forming. When vapor becomes liquid, it releases heat → so the system (dew) releases energy → exothermic.

So, marking it as Exo is correct.

Wait! But the explanation says: *"heat is released"* → that’s correct.

However, the system is dew, which is the product of condensation. Since the system releases heat, it’s exothermic.

✔ Exo is correct.

But the red X seems to indicate a correction. However, if the X is meant to mark wrong answers, this one is actually correct.

➡️ Conclusion: This is correctly marked as Exo.

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#### 6. Dynamite explodes in destruction of building
- System: Dynamite
- ✔ Exo (✔️ Correct)
- ✔️ Marked correctly

> Explanation: Explosion releases stored chemical energy → exothermic.

✔ Correct

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#### 7. Making ice cubes
- System: Water
- ✘ Marked as Exo (Incorrect)
- Should be: Endo

> Explanation: Water freezes → becomes ice. Freezing releases heat, but the system (water) loses energy → so it's exothermic?

Wait — let's clarify:

- When water freezes, it releases heat → so the system (water) is releasing energy → exothermic.

But the process of making ice cubes involves cooling water → removing heat from water → so the system (water) loses energy → exothermic.

So, Exo is correct.

But the worksheet has a red X next to Exo — suggesting it's wrong.

✘ But this is actually correct.

Wait — let's check the explanation: *"Heat is released from water"* → yes, during freezing, water releases heat.

So, Exo is correct.

→ Red X may be a mistake.

✔ Correct: Exo

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#### 8. A puddle of water evaporates
- System: Water
- ✘ Marked as Endo (✔️ Actually correct)
- But there’s a red X next to Endo — maybe indicating error?

> Evaporation: Liquid → gas → requires energy to break intermolecular forces → absorbs heat → endothermic.

✔ Endo is correct

So the red X is wrong — this should be Endo.

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#### 9. Plants making sugar through photosynthesis
- System: Plant
- ✘ Marked as Endo (✔️ Correct)
- Red X next to Endo — but this is correct

> Photosynthesis: CO₂ + H₂O + sunlight → glucose + O₂ → absorbs energy (sunlight) → endothermic

✔ Endo is correct

Red X is incorrect

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#### 10. Nuclear fission
- System: Nuclear reactor
- ✘ Marked as Exo (✔️ Correct)
- Red X — but this is correct

> Nuclear fission releases huge amounts of energy → exothermic

✔ Exo is correct

Red X is wrong

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#### 11. Converting heat to water vapor
- System: Heat?
- Wait — “heat” is not a system. That’s problematic.

Let’s re-read:
"Converting heat to water vapor" → probably means evaporating water using heat.

But system is listed as "heat"? That doesn't make sense.

Better interpretation: Water is heated to become vapor → system = water

Then:
- Water absorbs heat → endothermic

But system is labeled "heat" — which is not a physical substance.

This is poorly worded.

Assuming the system is water, then:
- Evaporation → Endo → ✔️ Correct

But the worksheet marks Endo with a red X — but it's correct.

So again, red X is incorrect

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#### 12. Melting solid sugar cubes
- System: Sugar cubes
- ✘ Marked as Endo (✔️ Correct)
- But red X — suggests it's wrong?

> Melting solid sugar → requires heat → absorbs energy → endothermic

✔ Endo is correct

So red X is wrong

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✔ Summary of Corrections:

| Row | Process | Correct Type | Worksheet Mark | Error? | Notes |
|-----|--------|--------------|----------------|--------|-------|
| 1 | Ice melts | Endo | Endo ✔ | No | Correct |
| 2 | Cooking egg | Endo | Endo ✔ | No | Correct |
| 3 | Burning match | Exo | Exo ✔ | No | Correct |
| 4 | Digestion | Exo | Exo ✔ | No | Correct |
| 5 | Dew forms | Exo | Exo ✔ | No | Correct (condensation releases heat) |
| 6 | Dynamite explodes | Exo | Exo ✔ | No | Correct |
| 7 | Making ice cubes | Exo | Exo ✔ | No | Correct (freezing releases heat) |
| 8 | Water evaporates | Endo | Endo ✔ | Yes | Red X is wrong |
| 9 | Photosynthesis | Endo | Endo ✔ | Yes | Red X is wrong |
| 10 | Nuclear fission | Exo | Exo ✔ | Yes | Red X is wrong |
| 11 | Converting heat to vapor | Endo | Endo ✔ | Yes | System mislabeled; red X wrong |
| 12 | Melting sugar | Endo | Endo ✔ | Yes | Red X is wrong |

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🛠️ Final Correction Guide:

The only real error is in Row 1:
- ✘ It was marked Exo (red X), but should be Endo.
- All other rows are correctly identified, but red Xs are incorrectly placed on correct answers.

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✔ Corrected Worksheet (Key Fixes):

| Process | System | Exo | Endo | Explanation |
|--------|--------|-----|------|-------------|
| 1. Ice melts | ice cube | | ✔ | Melting requires heat → endothermic |
| 2. Cooking egg | egg | | ✔ | Egg absorbs heat → endothermic |
| 3. Burning match | match | ✔ | | Releases heat → exothermic |
| 4. Digestion | food | ✔ | | Releases energy → exothermic |
| 5. Dew forms | dew | ✔ | | Condensation releases heat → exothermic |
| 6. Dynamite explodes | dynamite | ✔ | | Releases energy → exothermic |
| 7. Making ice cubes | water | ✔ | | Freezing releases heat → exothermic |
| 8. Water evaporates | water | | ✔ | Absorbs heat → endothermic |
| 9. Photosynthesis | plant | | ✔ | Absorbs sunlight → endothermic |
| 10. Nuclear fission | nuclear reactor | ✔ | | Releases energy → exothermic |
| 11. Evaporating water | water | | ✔ | Requires heat → endothermic |
| 12. Melting sugar | sugar cubes | | ✔ | Requires heat → endothermic |

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📝 Conclusion:

- Only Row 1 was incorrectly marked as Exo — it should be Endo.
- All other entries are correct, but red Xs were wrongly placed on correct answers.
- The explanations are mostly accurate, though some need refinement.

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💡 Tip for Students:

Always ask:
- Is energy going into the system? → Endothermic
- Is energy coming out of the system? → Exothermic

And remember: Phase changes like melting, evaporation, sublimation → Endo
Freezing, condensation, deposition → Exo

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Let me know if you'd like a cleaned-up version of the worksheet!