Heat, Temperature and Calorimetry

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Objective

SWBAT differentiate between heat energy and temperature and apply this knowledge to calorimetry.

Big Idea

The specific heat of a substance determines how much energy is required to change the temperature of a sample depending on its mass.

Background

This is the final unit of the year, and in many respects, could make for a great starter unit.  Calorimetry is all about intensive and extensive properties of matter, and could also be used to assess students' math readiness using simple algebra.

Regrettably, I only have 6 days of instruction left before final exams to explore this unit.  This short window limits me to a basic introduction of heat and matter and prevents me from connecting these ideas to bond energy, as I would in a full-length unit.

In the previous day students completed the PhET Energy Forms and Changes simulation and a modified worksheet downloaded from the site.  This is a good introduction to the concept as students can see that energy is different from temperature, and that different substances (brick, iron, water) absorb and hold different amounts of energy to change the same temperature increment.

These samples show how students noticed the blocks and water reached the same temperature when mixed, and that energy "E's" flow from the blocks to the water.

In the second part, students observe the energy flowing into the cold object from the warmer water.

Today's lesson utilizes a pencil and paper exercise, which may or may not be from POGIL.  The file was shared to me labeled as an "Old POGIL" but I have not been able to find a copy in my internet searches.  The diagrams are a little clunky, so they require some explanation before students begin.

This unit uses some pictorial models, so we access Science and Engineering Practice 2.  It also aligns with the Energy and Matter Cross Cutting Concept: Changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system.  In a larger context, this lesson begins our exploration of HS-PS3-4, plan and conduct an investigation to provide evidence that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system.

Opener: Setting the table

8 minutes

When students enter, I am returning their Energy Flows papers.  When the period begins, I explain that they did a pretty good job on the papers, but that I want to go over some things together.

I ask if the iron block and the brick absorbed the same amount of "E"s, which stood for energy.  Students reply that the brick held more.

  • Did both objects keep all their energy?
  • No, some escaped out.
  • What happened when you put a hot object into the water?
  • The water got hotter and gained energy from the object.
  • This unit is something you've experienced your whole life.  Think back to being little on the playground on a sunny day.  The sun shined all day on the metal slide, the black swing seat, and the green grass the same all day.  Which was the one that burned you when sat on it?
  • The slide
  • Which was coolest?
  • The grass.
  • This is because different objects hold and release heat differently, and change temperature differently because of their identity.  You saw this with the iron and brick on the computer simulation, but have noticed it your whole life without thinking too much about it.

I then start passing out the day's activity.

Paired Work

37 minutes

This is a three part activity.  Part 1 explores the relationship between the mass of a sample and the heat needed to boil it.  Part 2 explores the relationship between the heat needed to raise the temperature of a sample 30 degrees vs raising the temperature 70 degrees.  Part 3 introduces the lab technique of calorimetry and the heat equation, along with the definition of specific heat.

Once each student has a copy of the activity I explain today's procedure.

Students will work with a partner, but each person must complete a packet.  They are to work as an independent pair, and spread out so it's two to a table.  I explain that they should read and mark up the text, and then move on to the questions.

Before beginning, I explain the diagrams, as they are rather rudimentary.

  • In Part 1: Heat and Temperature, the diagrams represent two pots, A contains 1.00g of water, B contains 100g of water.
  • In Part 2, the diagrams represent pots with the exact same amount of water, but A is only at 50 degrees Celsius and B is at 90 degrees Celsius.
  • Part 3: Calorimetry shows a basic diagram of a calorimeter, used to measure changes in temperature when combining objects.
  • The Conclusions section contains four bullet points which must be addressed in their conclusion.

At this point, I release students to spread out and work.  I circulate the room to check their work and answer questions, often referring them back into the document. 

The most troublesome part of the front page was students remembering for #2 that water boils at 100 degrees Celsius.  This student mistook the amount of energy for the time it takes to boil.

Students quickly understood that the higher temperature with the same amount of matter meant there was more energy present.

One of the most common mistakes I saw students make was dropping the word "specific" when referring to specific heat.  This lead to some misconceptions in the following days.  That said, this student still ended up with a pretty solid definition.

Many students struggled with the heat calculations, as the equation was at the bottom of the previous page.  They also did not consistently remember to subtract to find the delta T, or to put Joules on their final answer to #4.  I had to correct a lot before passing these back.

When students got to the conclusions, they attacked it two different ways.  The first was to answer each part as its own bullet point like this student.

Others wrote a full paragraph response, incorporating the bullet points into the full paragraph.

Overall, students did well on differentiate temperature from heat, and identifying both mass and change in temperature as important in quantifying how much energy is in a sample.

Students had a more difficult time with the sample calculation, so I knew we would need some extra practice with them prior to getting to our full calorimetry lab.

Closing

5 minutes

With five minutes left, I stopped the class and asked them to explain what three things determine how much heat an object has:

  • Its size
  • More specific, what about it?
  • The mass
  • What else?
  • How much the temperature changed
  • What's the third part?
  • Can you give us a hint?
  • It was part of the equation, the part you have left out.
  • The specific heat?
  • Yes, that's what made the metal slide, the swing seat, and the grass feel different when you were little.  The metal, the plastic and the grass all have very different specific heats.  We're going to work more with that in the coming days.

I have students turn in their packets prior to leaving so I can grade them overnight.