Worksheet on endothermic and exothermic reactions with illustrated examples.

Let's solve the problem step by step, using your knowledge of endothermic and exothermic reactions.

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1. Complete the sentences using the words in the box:

Words available:
- energy
- heat
- chemicals
- transferred
- reactions
- decrease
- surroundings
- temperature
- increase

Now, fill in the blanks:

> Exothermic reactions transfer heat from the reacting chemicals into the surroundings.
> *(Explanation: Exothermic reactions release heat, so heat is transferred from the chemicals to the surroundings.)*

> We can measure the energy transferred by measuring the temperature increase in the reaction.
> *(Explanation: In exothermic reactions, the temperature of the surroundings increases; this rise in temperature indicates energy released.)*

> During endothermic reactions, there is a decrease in temperature.
> *(Explanation: Endothermic reactions absorb heat, so the surroundings cool down — temperature decreases.)*

> This is because energy is transferred from the surroundings into the reacting chemicals.
> *(Explanation: Energy is absorbed from the surroundings to break bonds in endothermic reactions.)*

✔ Completed sentences:

1. Exothermic reactions transfer heat from the reacting chemicals into the surroundings.
2. We can measure the energy transferred by measuring the temperature increase in the reaction.
3. During endothermic reactions there is a decrease in temperature.
4. This is because energy is transferred from the surroundings into the reacting chemicals.

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2. Label each reaction as endothermic or exothermic:

Let’s analyze each process:

#### Respiration
- This is the process where glucose is broken down in cells to release energy.
- It releases energy (ATP), so it's exothermic.
- 🔥 Exothermic

#### Neutralisation
- When an acid reacts with a base, heat is released.
- Example: HCl + NaOH → NaCl + H₂O + heat
- Always exothermic.
- 🔥 Exothermic

#### Photosynthesis
- Plants use sunlight to convert CO₂ and water into glucose and oxygen.
- Requires energy input (sunlight) → absorbs energy.
- So, it's endothermic.
- ☀️ Endothermic

#### Thermal decomposition
- A compound breaks down due to heat (e.g., heating limestone to make quicklime).
- Requires continuous heat input → absorbs energy.
- So, endothermic.
- 🔥 Endothermic

#### Burning fuels
- Combustion reactions (like burning coal or petrol) release heat and light.
- Strongly exothermic.
- 🔥 Exothermic

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✔ Final Answers for Part 2:

| Reaction | Type |
|------------------------|---------------|
| Respiration | Exothermic |
| Neutralisation | Exothermic |
| Photosynthesis | Endothermic |
| Thermal decomposition | Endothermic |
| Burning fuels | Exothermic |

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📌 Summary:

- Exothermic: Releases energy (usually heat), temperature increases.
- Endothermic: Absorbs energy, temperature decreases.

This worksheet helps reinforce understanding of how energy flows in chemical reactions.

Let me know if you'd like a printable version or further explanations!