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 …………………… from the reacting …………………… into the surroundings.

✔ Answer:
Exothermic reactions transfer energy from the reacting chemicals into the surroundings.

> We can measure the energy transferred by measuring the ………………………………………… increase in the reaction.

✔ Answer:
We can measure the energy transferred by measuring the temperature increase in the reaction.

> During endothermic …………………… there is a …………………… in temperature.

✔ Answer:
During endothermic reactions, there is a decrease in temperature.

> This is because energy is …………………… from the …………………… into the reacting chemicals.

✔ Answer:
This is because energy is transferred from the surroundings into the reacting chemicals.

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✔ Final completed sentences:

- Exothermic reactions transfer energy from the reacting chemicals into the surroundings.
- We can measure the energy transferred by measuring the temperature increase in the reaction.
- During endothermic reactions, there is a decrease in temperature.
- 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 a metabolic process where glucose is broken down to release energy.
- Energy is released (as heat), so it's exothermic.

✔ Answer: Exothermic

#### 🔹 Neutralisation
- This is when an acid reacts with a base to form salt and water.
- It releases heat → exothermic.

✔ Answer: Exothermic

#### 🔹 Photosynthesis
- Plants use sunlight to convert CO₂ and H₂O into glucose and oxygen.
- Requires energy input (sunlight) → endothermic.

✔ Answer: Endothermic

#### 🔹 Thermal decomposition
- A compound breaks down due to heat (e.g., heating limestone to make lime).
- Needs heat to proceed → endothermic.

✔ Answer: Endothermic

#### 🔹 Burning fuels
- Combustion reactions release heat and light.
- Classic example of exothermic reaction.

✔ Answer: 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 Explanation:

- Exothermic reactions: Release energy (usually as heat) → temperature increases.
Examples: Respiration, neutralisation, burning fuels.

- Endothermic reactions: Absorb energy from surroundings → temperature decreases.
Examples: Photosynthesis, thermal decomposition.

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✔ All answers are now complete and explained!