Worksheet on endothermic and exothermic reactions with fill-in-the-blank sentences and reaction labeling exercises.

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

---

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.

---

✔ 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.

---

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 ATP and heat).
- Exothermic

✔ Answer: Exothermic

#### 🔹 Neutralisation
- Reaction between an acid and a base produces salt and water.
- Releases heat (you can feel the flask get warm).
- Exothermic

✔ Answer: Exothermic

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

✔ Answer: Endothermic

#### 🔹 Thermal decomposition
- A compound breaks down due to heat (e.g., heating limestone to make quicklime).
- Needs continuous heat input.
- Endothermic

✔ Answer: Endothermic

#### 🔹 Burning fuels
- Combustion reaction (e.g., burning coal, petrol).
- Releases large amounts of heat and light.
- Exothermic

✔ Answer: Exothermic

---

✔ Final Answers for Part 2:

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

---

✔ Summary:

- Exothermic reactions release energy (usually heat), causing temperature to rise.
- Endothermic reactions absorb energy, causing temperature to drop.
- Examples:
- Exothermic: Respiration, neutralisation, combustion
- Endothermic: Photosynthesis, thermal decomposition

---

Let me know if you'd like this formatted as a printable answer sheet!