The Arizona STEM Acceleration Project

Mixing Hot and Cold: Investigating Energy Transfer

Mixing Hot and Cold: Investigating Energy Transfer

An 8th grade STEM lesson

Cassandra Cordts

July 25, 2023

Notes for teachers

• Prepare hot water in a coffee cisterne before class.
• Prepare cold water by keeping ice in a cooler. I have found mixing it at the beginning of class in pitchers produced the best result.
• Model pouring water - it seems simple but kids struggle with it every year.

List of Materials

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• Students Digital

Notebook Slides

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• Teacher Model

Slides

• For each group of students:
• 2 pipettes
• 3 styrofoam cups
• 1 500mL plastic cup
• 2 graduated cylinders
• glass thermometer
• prepared hot and cold water.

Standards

Core Ideas for Knowing Science:

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P1: All matter in the Universe is made of very small particles.

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P4: The total amount of energy in a closed system is always the same but can be transferred from one energy store to another during an event.

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Mathematical Practices

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3. Construct viable arguments and critique the reasoning of others.

4. Model with mathematics.

5. Use appropriate tools strategically.

6. Attend to precision.

8. Look for and express regularity in repeated reasoning.

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Standards

Physical Science Standards:

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8.P4U1.3 Construct an explanation on how energy can be transferred from one energy store to another.

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Educational Technology

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6-8.5.b. Students find and organize data and use technology to analyze and represent it to solve problems and make decisions.

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Objective:

Students will model transfer of kinetic energy by preparing and measuring the temperature of two equal quantities of water, before mixing them together and then measuring the final temperature.

Agenda

Objective: 1 minute

Agenda: 1 minutes

Introduction Activity: 5 minutes

Hands on Activity: 20 minutes

Connecting Observations: 15 minutes

Assessment: 10 minutes

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Intro/Driving Question/Opening

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Driving Question:

• If two equal volumes of hot and cold water are mixed, what will the final temperature be?

Scaffolded Opening Questions:

• Imagine you have one cup of hot water. The particles have a lot of kinetic energy. You have another cup of cold water. The particles do not have as much kinetic energy. If you mix them, what will happen to the kinetic energy particles?
• If you mixed 50 mL of 50°C hot water and 50 mL of 10°C cold water, what do you predict the temperature of the mixed water would be? Explain your thinking, what led you to make that prediction?

Hands-on Activity Instructions

• Students should work in groups of 2-4 depending on available materials.
• Depending on classroom set up have students walk to get or pass out 1 styrofoam cup with hot water and another with cold water to each group.
• Have students carefully measure 50 mL of hot water into one graduated cylinder and 50 mL of cold water into the other.
• Student will take and record the temperature of the hot and cold water using a glass thermometer.
• Students will pour the contents of the two graduated cylinders into the third (empty) foam cup. Placing the foam cup inside the larger plastic cup will keep it from tipping.
• Students will take and record the temperature of the hot and cold water mixture.
• Students will clean their lab space and share the results of their investigation with the class.

Connecting Observations to Abstract Concepts

• Have students look over their own data and the class data.
• Ask what patterns they see in the data.
• Use guiding questions:
• Looking at the data, can you see a pattern between the starting temperatures and the predicted temperatures in the results?
• What pattern did you find between starting and final temperatures?
• Can we express that as an (math) equation?
• Do you think that this would still work if there were 3 or 4 samples?
• Have students write an equation that explains the phenomena they observed.

• Add context with guiding questions:
• What happened to the hot water when it was mixed with the cold water?
• What happened to the cold water when it was mixed with the hot water?
• What happened to the kinetic energy of the particles in the hot water when the hot and cold water were mixed?
• What happened to the kinetic energy of the particles in the cold water when the hot and cold water were mixed?

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Assessment

Have students create a visual model (on paper or slides) to show what is happening at the particle level when you mix hot and cold water. Students can use colors and arrows to show what individual particles are doing.

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Differentiation

• This concept is difficult for some students to understand - being able to do the experiment twice often helps students who struggle.

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• This can also be done as a teacher-led model with guiding questions and students making observations - this would most likely need to be done in small group format.

Remediation

Extension/Enrichment

• Students can be asked to think of real life examples that they have seen this phenomenon has been seen before (food is a great hint).

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• Prompt students to think about how energy is transferred - what temperature is giving energy away? Which is receiving energy? How does this process work?

Student Work Slides

I use Google Slides to create a digital notebook with my students. Most days I use a copy of the same presentation that I have added animations and extra informational slides to if necessary. I have attached my student slides for this lesson to the slides that follow.

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2

(2 per group if possible)

1. Type here - make a numbered list of steps

You should have at least 5 steps!

Pointers:

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• Use the 2 foam cups to get hot and cold water.
• Measure the water using the graduated cylinders.
• You can pour the water into the graduated cylinder, but use the pipettes to get the water in the cylinders exactly even.
• Mix the hot and cold water in the third foam cup.
• Once you’ve mixed the water, put the third foam cup into the large, clear cup, which will keep it from tipping over when the thermometer is added.
• Read the temperature of the thermometer as soon as the alcohol in the thermometer stops moving.

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° C

° C

° C

° C

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Students at home: get your data from the video

screenshots. ---->

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T_f = T₁ + T₂ + T₃ +....+T_n

n

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Hot and Cold Particle Model

Using digital tools, make a model showing what is happening at the particle level when you mix hot and cold water.

Use shapes to create cups, use arrows to show energy transfer, and use color to show.