Changing Temperature -> Chemical Reaction

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Objective

SWBAT evaluate temperature change as exothermic or endothermic.

Big Idea

How do I know if a chemical reaction has occurred if I cannot see it?

The Need for This Lesson

Many middle school students are still very concrete thinkers. We need to provide opportunities for students to experience the definitions of chemical terms. 

In this lesson, students explore the meaning of exothermic and endothermic. Students can determine if a chemical reaction has occurred by recording any change in temperature.  By performing several mini experiments students have an opportunity to associate new vocabulary --exothermic and endothermic -- with concrete experiences here and now. Once the concrete experiences have occurred, students are no longer dependent on the here and now and can apply new vocabulary using logic and reasoning.

Investigation Preparation & Summary

10 minutes

Students will notice changes in temperature indicating that a chemical reaction has occurred. They will further be able to use exothermic and endothermic to describe the reaction (MS-PS1-2 Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.)  

Questions will be asked to encourage students to analyze their results as they explain how they identified whether or not a chemical reaction has occurred and they type of reaction (exothermic/endothermic) (SP4 Analyzing and Interpreting Data). Their evidence is derived from their careful observations of changes in temperature over time (SP7 - Engaging in Argument from Evidence).

My students have always been respectful of the materials we use in science experiments. I tell them early in the school year that their behavior will drive the type of experiments we can do in class. Nonetheless I am mindful that the unexpected does happen and make certain the the Material Safety Data Sheets are on hand. 

MSDS for Hydrogen Peroxide

MSDS for Epson Salts

MSDS for Vinegar

MSDS for Baking Soda

MSDS for Calcium Chloride

MSDS for Sodium Chloride (Salt)

The materials are numerous for this lesson. A complete Changing Temperatures Material List is available in the resources section.

Students in Action

45 minutes

This lesson has 7 mini experiments. In each of the experiments, we mix two ingredients and make a determination as to whether or not a chemical reaction has occurred.

First the vocabulary:

  • An exothermic reaction means that heat is released or sent out. The Greek word for heat is thermexo means outside, and the -ic suffix tells us that it has these characteristics. What do you think will happen to the temperature of the two ingredients if the reaction is exothermic? The temperature should show an increase overtime.
  • An endothermic reaction means that the heat is absorbed within. Again the Greek word for heat is therm, for within is endo and the  -ic suffix tells us that it has these characteristics. An endothermic reaction is essentially the opposite of an exothermic reaction. What do you think will happen to the temperature of the two ingredients if the reaction is endothermic? The temperature will show a decrease overtime. 

Focus Question: How will we know if no reaction has occurred? There is no change in temperature.

We review the procedures for the experiments. Students must wear goggles throughout the experiments until their work area is clean. Take the temperature of the first liquid before anything else is added. Record this number and make any observations about the liquid. Then add the second ingredient. Take the temperature again immediately. Record this number and make any observations. Repeat the recording of the temperature and observations after 1 minute, then again after 2 minutes. After 2 minutes you should be able to determine if a chemical reaction has occurred by evaluating the recorded temperatures.

Answer questions 8 and 9 -

  • Did a chemical reaction occur? a
  • What is your evidence? Use exothermic/endothermic in your response.

IMPORTANT - I say this with emphasis! You must make sure not to contaminate your tests. Use only the spoons provided for scooping the powders. Stir the ingredients with a Popsicle stick. Use this only once. After each experiment discard the liquid and rinse the cup and thermometer so no residue from the previous experiment is left behind to influence the results of your next experiment.

As students are working, I monitor their procedures to insure they are not contaminating the next experiment with left over liquid from the previous one. The students seem to understand this concern and are vigilant in their work.

A couple of student groups had unexpected results as I was making observations. I advised them to test again, this time either using less liquid or adding more of the second ingredient. Our biggest problem seems to be estimating 1/4 cup.

When students are waiting for a temperature check, I ask individual groups to name the elements in the chemical formulas supplied on the lesson sheet. They proudly name most of them correctly.  

In the following short video, I take a look at the different styles students use to record observations in the lesson and explain how we continue to practice naming elements.

Connecting the Learning

10 minutes

We conclude this lesson with a video from an expert to explain how exothermic and endothermic reactions are used in our everyday lives - especially when we are involved in sports or take a tumble in PE class!