Exothermic and endothermic reactions

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Lesson notes

Exothermic Reactions

**Exothermic reactions** transfer energy to the surroundings, usually as heat, causing a **temperature rise**.
Combustion is a key example: **fuel + oxygen → carbon dioxide + water**.
Neutralisation reactions (acid + metal oxide/hydroxide/carbonate → salt + water) are exothermic.
Oxidation reactions (metal + oxygen → metal oxide) are also exothermic.
Everyday uses include **hand warmers** and **self-heating cans**.

Endothermic Reactions

**Endothermic reactions** take in energy from the surroundings, causing a **temperature fall**.
Thermal decomposition is a key example: a compound breaks down when heated.
Instant cold packs use an endothermic reaction: water combines with another compound, absorbing heat.
These packs are used to treat sports injuries.

Comparing Exothermic and Endothermic

Exothermic: energy **transferred to** surroundings → temperature **rises**.
Endothermic: energy **taken from** surroundings → temperature **falls**.
Examples of exothermic: combustion, neutralisation, oxidation.
Examples of endothermic: thermal decomposition.

General Word Equations

Combustion: **fuel + oxygen → carbon dioxide + water**.
Neutralisation (acid + metal oxide): **acid + metal oxide → salt + water**.
Neutralisation (acid + metal hydroxide): **acid + metal hydroxide → salt + water**.
Neutralisation (acid + metal carbonate): **acid + metal carbonate → salt + carbon dioxide + water**.
Oxidation: **metal + oxygen → metal oxide**.

Particle arrangement in solids, liquids, and gases. Exothermic reactions often involve particles moving faster (more energy), while endothermic reactions involve particles slowing down (less energy).

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Practice questions

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1.What is an exothermic reaction?
Easy
- AA reaction that transfers energy to the surroundings
- BA reaction that takes in energy from the surroundings
- CA reaction that does not involve energy change
- DA reaction that only occurs when heated
2.Which of the following is an example of an exothermic reaction?
Easy
- ACombustion
- BThermal decomposition
- CPhotosynthesis
- DMelting ice
3.What is an endothermic reaction?
Easy
- AA reaction that takes in energy from the surroundings
- BA reaction that transfers energy to the surroundings
- CA reaction that produces a temperature increase
- DA reaction that always requires a catalyst
4.Which of the following is an example of an endothermic reaction?
Easy
- AThermal decomposition
- BBurning wood
- CNeutralisation
- DOxidation of iron
5.State whether the following statement is true or false: 'Oxidation is an example of an endothermic reaction.'
Medium
- AFalse
- BTrue
- CCannot be determined
- DIt depends on the substance
6.State whether the following statement is true or false: 'Thermal decomposition is an example of an endothermic reaction.'
Medium
- ATrue
- BFalse
- COnly if the compound is a carbonate
- DOnly if it produces a gas
7.State whether the following statement is true or false: 'Neutralisation is an example of an exothermic reaction.'
Medium
- ATrue
- BFalse
- COnly for acid-metal hydroxide reactions
- DOnly if a gas is produced
8.Complete the word equation: acid + metal hydroxide → ?
Medium
- Asalt + water
- Bsalt + hydrogen
- Csalt + carbon dioxide + water
- Dmetal oxide + water

More questions

9.The reaction between an acid and a metal hydroxide is classified as:
Medium
- AExothermic
- BEndothermic
- CNeither exothermic nor endothermic
- DEndothermic only if the acid is strong
10.Copper carbonate undergoes thermal decomposition. What is the reactant in this reaction?
Hard
- ACopper carbonate
- BCopper oxide
- CCarbon dioxide
- DOxygen
11.In the thermal decomposition of copper carbonate, what are the products?
Hard
- ACopper oxide and carbon dioxide
- BCopper and carbon dioxide
- CCopper oxide and oxygen
- DCopper and oxygen
12.Complete the chemical equation: CuCO3 → CuO + ?
Hard
- ACO2
- BCO
- CC
- DO2
13.A student measures the temperature change in a reaction and finds it decreases from 25°C to 18°C. Which type of reaction is this?
Medium
- AExothermic
- BEndothermic
- CNeutralisation
- DCombustion
14.In a self-heating can, a chemical reaction produces heat. Which type of reaction is used?
Medium
- AEndothermic
- BExothermic
- CThermal decomposition
- DOxidation
15.An instant cold pack contains water and another compound. When the pack is squeezed, the temperature drops. This is an example of:
Medium
- AAn exothermic reaction
- BAn endothermic reaction
- CCombustion
- DNeutralisation
16.A reaction occurs in a beaker and the temperature rises from 20°C to 35°C. Which of the following is most likely the reaction?
Hard
- AThermal decomposition of copper carbonate
- BDissolving ammonium nitrate in water
- CBurning methane in oxygen
- DPhotosynthesis
17.In an experiment, 0.5 g of magnesium is burned in air. The temperature of the surroundings increases by 8°C. Which statement is correct?
Hard
- AThe reaction is endothermic because it takes in energy.
- BThe reaction is exothermic because it releases energy.
- CThe reaction is endothermic because the temperature increases.
- DThe reaction is exothermic because the temperature decreases.
18.The general word equation for combustion is: fuel + oxygen → carbon dioxide + water. Which type of reaction is combustion?
Medium
- AEndothermic
- BExothermic
- CThermal decomposition
- DNeutralisation
19.In a neutralisation reaction between an acid and a metal hydroxide, the temperature of the mixture increases. This shows that neutralisation is:
Easy
- AEndothermic
- BExothermic
- CNeither exothermic nor endothermic
- DAlways endothermic
20.A student adds 50 cm³ of hydrochloric acid to 50 cm³ of sodium hydroxide solution and records a temperature rise of 4°C. Which of the following changes would produce the largest temperature rise?
Medium
- AUsing 25 cm³ of acid and 75 cm³ of alkali
- BUsing 100 cm³ of acid and 100 cm³ of alkali
- CUsing 50 cm³ of acid and 50 cm³ of water
- DUsing 50 cm³ of acid and 50 cm³ of alkali at a lower starting temperature
21.The reaction between zinc and hydrochloric acid produces zinc chloride and hydrogen gas. The temperature of the mixture increases. Which equation correctly represents this reaction?
Hard
- AZn + 2HCl → ZnCl₂ + H₂ + energy
- BZn + 2HCl + energy → ZnCl₂ + H₂
- CZn + HCl → ZnCl + H
- D2Zn + 2HCl → 2ZnCl + H₂
22.Copper carbonate decomposes when heated: CuCO₃ → CuO + CO₂. During the reaction, the temperature of the surroundings decreases. This reaction is:
Medium
- AExothermic
- BEndothermic
- CNeutralisation
- DCombustion
23.A student investigates the temperature change when 5 g of ammonium nitrate is dissolved in 50 cm³ of water. The temperature drops from 22°C to 16°C. Which statement explains this?
Hard
- AThe process is exothermic because energy is released.
- BThe process is endothermic because energy is absorbed.
- CThe process is exothermic because the temperature decreases.
- DThe process is endothermic because the temperature increases.
24.A student adds 50 cm³ of hydrochloric acid to 50 cm³ of sodium hydroxide solution in a polystyrene cup. The initial temperature of both solutions is 21.0°C. After stirring, the highest temperature reached is 27.5°C. What is the temperature change?
Medium
- A6.5°C increase
- B6.5°C decrease
- C48.5°C increase
- D27.5°C increase
25.In an experiment to investigate the temperature change of a neutralisation reaction, which piece of equipment is most suitable for measuring the temperature accurately?
Medium
- AA thermometer with a range of -10°C to 110°C
- BA thermometer with a range of 0°C to 50°C
- CA data logger with a temperature probe
- DA mercury-in-glass thermometer
26.A student investigates the reaction between magnesium ribbon and hydrochloric acid. They measure the temperature change and the volume of hydrogen gas produced. Which of the following is a valid conclusion if the temperature increases and gas is produced?
Hard
- AThe reaction is exothermic and produces hydrogen gas.
- BThe reaction is endothermic and produces hydrogen gas.
- CThe reaction is exothermic and consumes hydrogen gas.
- DThe reaction is endothermic and consumes hydrogen gas.
27.In a self-heating can, the chemical reaction used is typically the reaction of calcium oxide with water. Which statement about this reaction is correct?
Medium
- AIt is exothermic because it releases heat.
- BIt is endothermic because it absorbs heat.
- CIt is exothermic because it absorbs heat.
- DIt is endothermic because it releases heat.
28.A student places 10 g of ammonium nitrate in a beaker and adds 50 cm³ of water. The temperature drops from 22°C to 14°C. Which of the following explains this observation?
Hard
- AThe dissolution of ammonium nitrate is endothermic; energy is taken from the surroundings, causing the temperature to decrease.
- BThe dissolution of ammonium nitrate is exothermic; energy is released to the surroundings, causing the temperature to decrease.
- CThe dissolution of ammonium nitrate is endothermic; energy is released to the surroundings, causing the temperature to decrease.
- DThe dissolution of ammonium nitrate is exothermic; energy is taken from the surroundings, causing the temperature to decrease.
29.Which of the following is a valid method to reduce heat loss to the surroundings in an exothermic reaction experiment?
Medium
- AUse a polystyrene cup as a container.
- BStir the mixture vigorously.
- CUse a metal container instead of a plastic one.
- DLeave the container open to the air.
30.A student measures the temperature change when 5 g of potassium nitrate is dissolved in 25 cm³ of water. The temperature falls by 8°C. Which of the following changes would result in a larger temperature fall?
Medium
- AUsing 10 g of potassium nitrate instead of 5 g.
- BUsing 50 cm³ of water instead of 25 cm³.
- CUsing 5 g of potassium nitrate at a higher initial temperature.
- DStirring the mixture more slowly.
31.A student wants to compare the temperature changes of two different exothermic reactions. Which experimental procedure is most appropriate?
Hard
- AUse the same mass of reactants and the same volume of solvent, and measure the maximum temperature reached.
- BUse different masses of reactants but the same volume of solvent, and measure the temperature change.
- CUse the same mass of reactants but different volumes of solvent, and measure the temperature change.
- DUse different masses of reactants and different volumes of solvent, and measure the final temperature.
32.Thermal decomposition of calcium carbonate is an endothermic reaction. Which of the following statements is correct?
Medium
- AThe temperature of the surroundings decreases because the reaction absorbs energy.
- BThe temperature of the surroundings increases because the reaction releases energy.
- CThe temperature of the surroundings decreases because the reaction releases energy.
- DThe temperature of the surroundings increases because the reaction absorbs energy.
33.In an experiment, 0.5 g of magnesium is burned in air. The temperature of 100 g of water in a container increases by 8°C. Which statement is correct?
Hard
- AThe combustion of magnesium is exothermic; it releases energy that heats the water.
- BThe combustion of magnesium is endothermic; it absorbs energy from the water.
- CThe combustion of magnesium is exothermic; it absorbs energy from the water.
- DThe combustion of magnesium is endothermic; it releases energy that heats the water.
34.A student adds 50 cm³ of hydrochloric acid to 50 cm³ of sodium hydroxide solution and records a temperature rise of 4°C. Which of the following changes would produce a temperature rise of about 8°C?
Medium
- AUsing 100 cm³ of hydrochloric acid and 100 cm³ of sodium hydroxide solution.
- BUsing 50 cm³ of hydrochloric acid and 50 cm³ of sodium hydroxide solution, but with double the concentration of both.
- CUsing 100 cm³ of hydrochloric acid and 50 cm³ of sodium hydroxide solution.
- DUsing 50 cm³ of hydrochloric acid and 50 cm³ of sodium hydroxide solution, but with half the concentration of both.
35.A student investigates the reaction between zinc and copper sulfate solution. The temperature of the mixture increases. Which of the following is the correct interpretation?
Hard
- AThe reaction is exothermic; zinc displaces copper, and energy is released.
- BThe reaction is endothermic; zinc displaces copper, and energy is absorbed.
- CThe reaction is exothermic; copper displaces zinc, and energy is released.
- DThe reaction is endothermic; copper displaces zinc, and energy is absorbed.
36.What is the general word equation for combustion?
Easy
- Afuel + oxygen → carbon dioxide + water
- Bfuel + oxygen → carbon monoxide + water
- Cfuel + carbon dioxide → oxygen + water
- Dfuel + water → carbon dioxide + oxygen
37.Which of the following statements about thermal decomposition is correct?
Easy
- AIt is an endothermic reaction.
- BIt is an exothermic reaction.
- CIt releases energy to the surroundings.
- DIt causes a temperature increase.
38.In a neutralisation reaction between an acid and a metal hydroxide, the temperature of the mixture increases. What type of reaction is this?
Medium
- Aexothermic
- Bendothermic
- Cthermal decomposition
- Doxidation
39.A student squeezes an instant cold pack, causing the inner bag to burst. The temperature of the pack drops rapidly. Which type of reaction is occurring?
Medium
- Aexothermic
- Bendothermic
- Ccombustion
- Dneutralisation
40.Which of the following word equations represents an exothermic reaction?
Medium
- Acalcium carbonate → calcium oxide + carbon dioxide
- Bcopper carbonate → copper oxide + carbon dioxide
- Cmagnesium + oxygen → magnesium oxide
- Dammonium nitrate + water → ammonium nitrate solution

Revision notes

## Exothermic and Endothermic Reactions ### Exothermic Reactions - **Definition**: Reactions that **transfer energy to the surroundings**, usually by heating, causing a **temperature rise**. - **Examples**: - **Combustion**: fuel + oxygen → carbon dioxide + water - **Neutralisation**: acid + metal oxide/hydroxide/carbonate → salt + water (+ CO₂ if carbonate) - **Oxidation**: metal + oxygen → metal oxide - **Uses**: hand warmers, self-heating cans. ### Endothermic Reactions - **Definition**: Reactions that **take in energy from the surroundings**, causing a **temperature fall**. - **Example**: **Thermal decomposition** – a compound breaks down into simpler products when heated. - **Uses**: instant cold packs (e.g., water + compound in inner bag). ### Key Equations - Combustion: fuel + oxygen → carbon dioxide + water - Neutralisation (acid + metal hydroxide): acid + metal hydroxide → salt + water - Oxidation: metal + oxygen → metal oxide - Thermal decomposition (e.g., copper carbonate): CuCO₃ → CuO + CO₂

Exothermic reaction: A chemical reaction that transfers energy to the surroundings, usually by heating, causing a rise in temperature.
Endothermic reaction: A chemical reaction that takes in energy from the surroundings, causing a fall in temperature.
Combustion: An exothermic reaction where a fuel burns in oxygen, producing carbon dioxide and water.
Neutralisation: An exothermic reaction between an acid and a base (metal oxide, hydroxide, or carbonate) producing a salt and water (and carbon dioxide if carbonate).
Oxidation: An exothermic reaction where a metal combines with oxygen to form a metal oxide.
Thermal decomposition: An endothermic reaction where a compound is heated and breaks down into smaller, simpler products.

Flashcards

What is an exothermic reaction?

A chemical reaction that transfers energy to the surroundings, usually by heating, causing a rise in temperature.

What is an endothermic reaction?

A chemical reaction that takes in energy from the surroundings, resulting in a fall in temperature.

Give two examples of exothermic reactions.

Combustion and neutralisation.

Give an example of an endothermic reaction.

Thermal decomposition.

What is the general word equation for combustion?

fuel + oxygen → carbon dioxide + water

What is the general word equation for neutralisation of an acid with a metal oxide?

acid + metal oxide → salt + water

What is the general word equation for neutralisation of an acid with a metal hydroxide?

acid + metal hydroxide → salt + water

What is the general word equation for neutralisation of an acid with a metal carbonate?

acid + metal carbonate → salt + carbon dioxide + water

What is the general chemical equation for a metal undergoing oxidation?

metal + oxygen → metal oxide

What is thermal decomposition?

When a compound is heated and breaks down into smaller and simpler products.

Give an everyday application of an exothermic reaction.

Hand warmers and self-heating cans of hot drinks.

Give an everyday application of an endothermic reaction.

Instant cold packs used to treat sports injuries.

How does an instant cold pack work?

It contains two bags (one inside the other) – one with water and one with a compound. When the inner bag bursts, water combines with the compound, causing an endothermic reaction that decreases temperature.

Is oxidation exothermic or endothermic?

Exothermic (oxidation reactions are exothermic).

Is thermal decomposition exothermic or endothermic?

Endothermic.

Is neutralisation exothermic or endothermic?

Exothermic.

Complete: acid + metal hydroxide → ? + ?

salt + water

Copper carbonate undergoes thermal decomposition. What is the reactant?

Copper carbonate (CuCO₃).

Copper carbonate undergoes thermal decomposition. What are the products?

Copper oxide (CuO) and carbon dioxide (CO₂).

Complete: CuCO₃ → CuO + ?

CO₂

Is the thermal decomposition of copper carbonate exothermic or endothermic?

Endothermic.

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