New
New
Year 8

Exothermic and endothermic chemical reactions

I can identify whether a chemical reaction is exothermic or endothermic and explain how I know.

New
New
Year 8

Exothermic and endothermic chemical reactions

I can identify whether a chemical reaction is exothermic or endothermic and explain how I know.

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Lesson details

Key learning points

  1. An exothermic chemical reaction causes an increase in temperature (of the surroundings).
  2. An endothermic chemical reaction causes a decrease in temperature (of the surroundings).
  3. An exothermic reaction transfers energy from the reactants to the surroundings.
  4. An endothermic reaction transfers energy from the surroundings to the products.

Keywords

  • Exothermic chemical reaction - is a type of reaction in which energy is transferred from the reactants to the surroundings, e.g. combustion.

  • Endothermic chemical reaction - is a type of reaction in which energy from the surroundings is transferred to the products, e.g. photosynthesis.

  • Dissipate - Thermal energy can dissipate which means it can be transferred to the environment and wasted.

Common misconception

The difference between the surroundings (where the reaction takes place, e.g. solution) and the environment (where the reaction mixture is, e.g. classroom). The existence of cold.

Use the separate terms of surroundings and environment throughout the lesson. Explain that thermal energy transfer only takes place from somewhere that is warmer and somewhere that is cooler.

Demonstrate the classic endothermic reaction between solid hydrated barium hydroxide and solid ammonium chloride, ensure this is practiced and risk assessed prior to the lesson.
Teacher tip

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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6 Questions

Q1.
Match the following terms to their definitions.
Correct Answer:reactant,substance present at the start of a chemical reaction

substance present at the start of a chemical reaction

Correct Answer:product,substance made during a chemical reaction

substance made during a chemical reaction

Correct Answer:chemical reaction,when chemical bonds are broken and new substances are formed

when chemical bonds are broken and new substances are formed

Correct Answer:physical change,a reversible process that does not involve breaking chemical bonds

a reversible process that does not involve breaking chemical bonds

Q2.
True or false? A change of state indicates that a chemical reaction has taken place.
true
Correct answer: false
Q3.
Which of the following are examples of chemical reactions?
Correct answer: oxidation
Correct answer: thermal decomposition
evaporation
condensation
Q4.
Hydrogen gas and magnesium chloride are formed when magnesium reacts with hydrochloric acid. Which of the following represents the chemical equation for the reaction?
Correct answer: magnesium + hydrochloric acid → magnesium chloride + hydrogen
magnesium chloride + hydrogen → magnesium + hydrochloric acid
magnesium chloride + hydrochloric acid → magnesium + hydrogen
hydrochloric acid + hydrogen → magnesium + magnesium chloride
Q5.
Burning is an example of ... Select two correct answers.
Correct answer: a combustion reaction.
a neutralisation reaction.
a thermal decomposition reaction.
Correct answer: an oxidation reaction.
Q6.
Calculate the mass of carbon dioxide formed when 13.5 g of calcium carbonate reacts to form 7.6 g of calcium oxide. calcium carbonate → calcium oxide + carbon dioxide
Correct Answer: 5.9 g, 5.9

6 Questions

Q1.
Match the following terms to their definitions.
Correct Answer:exothermic chemical reaction,energy is transferred from the reactants to the surroundings

energy is transferred from the reactants to the surroundings

Correct Answer:endothermic chemical reaction,energy from the surroundings is transferred to the products

energy from the surroundings is transferred to the products

Correct Answer:dissipate,energy is transferred (and lost) as 'heat' to the environment

energy is transferred (and lost) as 'heat' to the environment

Q2.
Endothermic reactions cause ...
an increase in temperature of the surroundings.
Correct answer: a decrease in temperature of the surroundings.
the temperature of the surroundings to remain the same.
Q3.
Which of the following are reactions that are usually exothermic?
Correct answer: combustion
thermal decomposition
Correct answer: neutralisation
photosynthesis
Q4.
The method for finding the lowest temperature of a reaction has been mixed up. Starting with measuring the volume of solution, sort the following steps into the correct order.
1 - Measure 100 cm³ of copper sulfate solution into a polystyrene beaker.
2 - Measure the temperature of the solution.
3 - Add 2 g of ammonium nitrate powder.
4 - Stir the solution until all of the ammonium nitrate has dissolved.
5 - Measure the temperature of the reaction mixture.
6 - Record the lowest temperature reached by the solution.
Q5.
A pupil monitored the temperature of a reaction. The start temperature was 20°C and the end temperature 15°C. Which of the following statements about the reaction are correct?
The reaction is exothermic.
Correct answer: The difference in temperature is –5 °C.
Correct answer: Energy is transferred from the surroundings to the products.
The temperature of the surroundings increased.
Q6.
True or false? After an exothermic reaction, the products of the reaction contain more energy than the reactants.
true
Correct answer: false