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Lesson 10 Endothermic and Exothermic Reactions

Site: MoodleHUB.ca 🍁
Course: Science 10 [5 cr] - AB Ed copy 1
Book: Lesson 10 Endothermic and Exothermic Reactions
Printed by: Guest user
Date: Sunday, 7 September 2025, 6:43 PM

Table of contents

  Introduction

How can you identify that a chemical reaction has occurred?



B9.1 egg boiling in water
A pot of water boiling on the stove creates gas bubbles; however, this is a physical change, not a chemical reaction. When an egg is placed in the boiling water, the proteins in the egg will undergo a chemical reaction and change from a gel-like liquid into a firm solid.

In this lesson, you will learn how to identify a change as a chemical reaction, based on observations.

  Targets

By the end of this lesson, you will be able to

  • describe the evidence for chemical changes
  • differentiate between exothermic and endothermic reactions

  Watch This

Blue-Bottle Reaction @ Wikimedia https://adlc.wistia.com/medias/6lfuv7xqlc


Watch this video that will introduce you into the world of chemical changes. What evidence do you see that would indicate that this is a chemical change? Is there evidence that would indicate that this is not a chemical change? This will help get you in the right mindset for this lesson.

The colour change would indicate a chemical reaction has occurred. However, it appears to be easily reversed.
 

  Evidence of a Chemical Reaction

What specific evidence will indicate that a chemical reaction has occurred?



© Wikimedia Commons
B10.2 Yellow precipitate forming in a test tube
There are several key pieces of evidence that can be collected that indicate that a chemical reaction has occurred.

  1. A new substance with unique properties is created.
  2. The process is difficult to reverse.
  3. A gas is produced.
  4. A precipitate is formed when two solutions are combined.
  5. A new odour is detected.
  6. A colour change is observed.
  7. A change in temperature is measured.

At times, you may observe one of these pieces of evidence; however, it may not definitively indicate that there was a chemical reaction. Think of a pot of water boiling; even though gas bubbles are produced, it is not a chemical change but instead a phase change from liquid water to water vapour.

A key technique to help you identify if the evidence supports the identification of a chemical change is to ask yourself, “Was a new substance formed?” and “Is the process difficult to reverse?” In the case of the boiling water, no new substance was produced; it is still water, and by simply cooling the water vapour, you will recreate liquid water.

Watch these examples of chemical changes.

Is There a Chemical Change? Part I @ YouTube CDPEatUCO 


Watch this video to observe evidence of a chemical reaction.

Is There a Chemical Change? Part II @ YouTube CDPEatUCO 


Watch this video to observe evidence of a chemical reaction.

Is There a Chemical Change? Part IV @ YouTube CDPEatUCO 


Watch this video to observe evidence of a chemical reaction.


  Read This

Please read pages 15, 17, and 84 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on identifying evidence that indicates a chemical reaction occurred. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

Complete the following practice question to check your understanding of the concept you just learned. Make sure you write a complete answer to the practice question in your notes. After you have checked your answer, make corrections to your response (where necessary) to study from.

  1. Write down four observations that could provide evidence that a chemical reaction has taken place.

    Four observations that could indicate that a chemical reaction has occurred are a colour change, the formation of a gas, the formation of a precipitate, and a temperature change.
  2. What is the only real proof that a chemical reaction has occurred?

    The only real proof is if a new substance is formed that has properties different than the reactants.

  Endothermic Versus Exothermic Reactions

Energy can either be absorbed or released during a chemical reaction.



B10.3 Flame
If energy is released during a chemical reaction, it is identified as an exothermic change and an energy term can be written on the product side of the chemical reaction equation. For example, the combustion of natural gas (methane) in figure B10.3 has the reaction equation as follows:

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + energy

If energy is absorbed during a chemical reaction, it is identified as an endothermic change and an energy term can be written on the reactant side of the chemical reaction equation. For example, the process of photosynthesis is an endothermic reaction and requires the input of energy (sunlight); its reaction equation is as follows:

6CO2(g) + 6H2O(l) + energy → C6H12O6(g) + 6O2(g)

Heat is one form of energy; energy can also take the form of light. Some reactions will produce or absorb both light and heat.
B10.4 Leaf absorbing sunlight

  Read This

Please read page 81 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on identifying endothermic and exothermic reactions. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

Complete the following practice question to check your understanding of the concept you just learned. Make sure you write a complete answer to the practice question in your notes. After you have checked your answer, make corrections to your response (where necessary) to study from.

  1. Identify the following reactions as endothermic or exothermic.

    1. Farai is holding onto an Erlenmeyer flask containing a solution. When a second solution is poured in, the Erlenmeyer flask starts to feel warmer. Would this reaction be endothermic or exothermic?

      Exothermic; energy must be being released or given off if it feels warmer.
    2. S8(s) + 8O2(g) → 8SO2(g) + heat

      Exothermic; the energy term is on the product side.
    3. Water can be decomposed into hydrogen gas and oxygen gas when an electric current is applied to it.

      Endothermic; energy, in the form of an electric current, is added.
    4. N2(g) + O2(g) + heat → 2NO(g)

      Endothermic; the energy term is a reactant.


  Conclusion

Visual observations can readily indicate the occurrence of a chemical reaction.



B10.5 A pink substance is formed when two clear, colourless liquids are mixed.
The most important piece of evidence that indicates a chemical reaction occurred is the formation of a new substance with unique properties. Some of those properties may be a different colour, state, odour, or temperature. Sometimes, you need to look at several pieces of evidence to accurately conclude whether or not a chemical reaction has occurred.

In the next lesson, you will look at how to identify the types of chemical reactions that can occur.

  Virtual Lab

Chemical Changes @ Explore Learning


Background Information:

Please work through this lab to observe evidence of chemical reactions.

Please note: if you scroll down while in the Gizmo you will see a list of questions. You DO NOT need to complete these questions. You are able to complete them for extra practice if you would like.


  1. Click on the play icon to open the virtual lab or go to the Online Resources for Print Students section in your online course.
  2. For “Reactant 1” select “Sodium.”
  3. For “Reactant 2” select “Water.”
  4. Select “Gas collection.” Then select “Label reactants,” “Show chemical equation,” and “Show balanced equation” (which appears after “Show chemical equation” is selected).
  5. Drag the thermometer on top of the Erlenmeyer flask.
  6. Record the appearance of the reactants. Record the initial mass. Record the initial temperature.
  7. Click on the play icon.
  8. Record your observations of any changes to the appearance of the substances. If you want to watch the reaction again, click the replay button.
  9. Record the final mass and the final temperature.
  10. Select “Glowing splint” and drag it to the top of the test tube.
  11. Record your observations.
  12. Click on the procedure 2 tab to continue.

    Observation
    appearance of reactant 1
    grey solid
    appearance of reactant 2
    clear, colourless liquid
    initial mass (g)
    2 417.0
    initial temperature (°C)
    observation of reaction
    Bubbles are produced.
    Grey solid disappears.
    final mass (g)
    2 417.0
    final temperature (°C)
    diagnostic test (glowing splint) result
    A pop is heard. Glowing split causes small explosion.
  1. For “Reactant 1” select “Hydrogen peroxide.”
  2. For “Reactant 2” select “Potassium iodide.”
  3. Select “Gas collection.” Then select “Label reactants,” “Show chemical equation,” and “Show balanced equation.”
  4. Drag the thermometer on top of the Erlenmeyer flask.
  5. Record the appearance of the reactants. Record the initial mass. Record the initial temperature.
  6. Click on the play icon.
  7. Record your observations of any changes to the appearance of the substances. If you want to watch the reaction again, click the replay button.
  8. Record the final mass and the final temperature.
  9. Select “Glowing splint” and drag it to the top of the test tube.
  10. Record your observations.
  11. Click on the procedure 3 tab to continue.

    Observation
    appearance of reactant 1
    clear, colourless liquid
    appearance of reactant 2
    clear, yellow liquid
    initial mass (g)
    2 401.6
    initial temperature (°C)
    observation of reaction
    Solution colour changes to brown then back to yellow.
    Bubbles are produced.
    final mass (g)
    2 401.6
    final temperature (°C)
    diagnostic test (glowing splint) result
    Glowing splint ignites.
  1. For “Reactant 1” select “Silver nitrate.”
  2. For “Reactant 2” select “Hydrochloric acid.”
  3. Select “Normal setup.” Then select “Label reactants,” “Show chemical equation,” and “Show balanced equation.”
  4. Record the appearance of the reactants. Record the initial mass.
  5. Click on the play icon.
  6. Record your observations of any changes to the appearance of the substances. If you want to watch the reaction again, click the replay button.
  7. Record the final mass.
  8. Click on the procedure 4 tab to continue.

    Observation
    appearance of reactant 1
    clear, colourless liquid
    appearance of reactant 2
    clear, colourless liquid
    initial mass (g)
    360.0
    observation of reaction
    White precipitate forms.
    final mass (g)
    360.0

  1. For “Reactant 1” select “Silver nitrate.”
  2. For “Reactant 2” select “Copper.”
  3. Select “Normal setup.” Then select “Label reactants,” “Show chemical equation,” and “Show balanced equation.”
  4. Record the appearance of the reactants. Record the initial mass.
  5. Click on the play icon.
  6. Drag the magnifier over top of the Erlenmeyer flask.
  7. Record your observations of any changes to the appearance of the substances. If you want to watch the reaction again, click the replay button.
  8. Record the final mass.
  9. Click on the procedure 5 tab to continue.

    Observation
    appearance of reactant 1
    clear, colourless liquid
    appearance of reactant 2
    copper-coloured coil
    initial mass (g)
    observation of reaction
    Solution turns blue.
    White crystals form.
    final mass (g)
  1. For “Reactant 1” select “Sodium.”
  2. For “Reactant 2” select “Chorine.”
  3. Select “Closed system.” Then select “Label reactants,” “Show chemical equation,” and “Show balanced equation.”
  4. Record the appearance of the reactants. Record the initial mass.
  5. Click on the play icon.
  6. Drag the magnifier over top of the Erlenmeyer flask.
  7. Record your observations of any changes to the appearance of the substances. If you want to watch the reaction again, click the replay button.
  8. Record the final mass.
  9. Click on the procedure 6 tab to continue.

    Observation
    appearance of reactant 1
    grey solid
    appearance of reactant 2
    yellow gas
    initial mass (g)
    1 351.1
    observation of reaction
    Flames form.
    A white crystal forms.
    final mass (g)
    1 351.1
  1. For “Reactant 1” select “Ammonium nitrate.”
  2. For “Reactant 2” select “Potassium hydroxide.”
  3. Select “Gas collection.” Then select “Label reactants,” “Show chemical equation,” and “Show balanced equation.”
  4. Drag the thermometer on top of the Erlenmeyer flask.
  5. Drag Phenol red on top of the Erlenmeyer flask.
  6. Record the appearance of the reactants. Record the initial mass. Record the initial temperature. Record the initial pH.
  7. Click the play icon.
  8. Record your observations of any changes to the appearance of the substances. If you want to watch the reaction again, click the replay button.
  9. Record the final mass and the final temperature.
  10. Select “Glowing splint” and drag it to the top of the test tube.
  11. Record your observations.
  12. Drag the nose onto the test tube.
  13. Record your observations.

    Observation
    appearance of reactant 1
    white powder
    appearance of reactant 2
    clear, colourless liquid
    initial mass (g)
    2 867.0
    initial temperature (°C)
    phenol red results
    pink colour—basic
    observation of reaction
    Bubbles are formed.
    final phenol red results
    yellow colour—neutral
    final mass (g)
    2 867.0
    final temperature (°C)
    glowing splint test
    Splint is extinguished.
    odour
    There is a strong smell of ammonia.


2.6 Assignment

Unit 2 Assignment Lessons 10-13

It is now time to complete the Lesson 10 portion of 2.6 Assignment. This assignment has two parts.

  1. Part 1 Written Portion: Select the preferred document type from the options below. Download and save the assignment on your desktop (or documents folder).

    PDF Document       
  2. Open and print this saved document.
  3. Record your responses in the appropriate textboxes.
  4. When you have completed the assignment, scan it and save it on your desktop (or documents folder).
  5. Once you have completed the written portion of your assignment, click on the button below to go to the submission page.

    Written Portion Submission Page
  6. Part 2 Online Portion: It is now time to complete the Lesson 5 questions of the online portion of this assignment. Click on the button below to go to the online questions of this assignment.

    Online Questions

This assignment is worth ___% of your final grade.