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## Comparing Thermodynamic Terms: Instructor's Guide

### Main Ideas

• Temperature
• Energy
• Heat
• Entropy

Estimated Time: 15 minutes

Students are given several small white board questions and asked to note the difference between temperature, energy, heat, and entropy.

### Prerequisite Knowledge

• Experience with work, energy, temperature, and entropy in any context is useful.

### Activity: Introduction

This series of questions works well with little introduction or lead-in. The class is asked the questions:

1. SWBQ: “What is energy? What kind of a thing is energy?”
2. SWBQ: “What is entropy? What kind of a thing is entropy?”
3. SWBQ: “What is temperature? What kind of a thing is temperature?”
4. SWBQ: “What is heat? What kind of a thing is heat?

The instructor should collect white boards after each question is asked so that student answers can be compared and discussed. A short discussion on the similarities and differences between temperature, energy, and heat can occur before the question on entropy since entropy is typically the more challenging question of the four.

### Activity: Student Conversations

Here are some possible student answers:

Energy:

• $\frac12 mv^2$
• $\int \vec{F}\cdot \vec{dr}$
• It is conserved.
• I'm sure there are more that I am not thinking of.

Entropy:

• Disorder/Messiness/Randomness
• Something that always increases.
• I'm sure there is more

Temperature:

• It is the same for objects in equilibrium.
• Measures how hot things are.
• Kinetic energy.
• Greater than absolute zero
• Celsius/Kelvin/Fahrenheit
• I'm sure there is more

Heat:

• A form of energy.
• Makes things hot.
• Relates to size and temperature (Match and campfire are the same temperature, but have different heat)
• I'm sure there is more

Possible conversations

Energy:

• How many forms could it take?
• How do we know if it is something “real”?
• Can we measure energy? Changes in energy? How?
• Is energy a property of an object, like mass?

Entropy:

• How would you quantify disorder? (if that is entropy)
• When might entropy decrease?
• If entropy increases, where does it come from?
• Can we measure entropy? Changes in entropy? How?
• Is entropy a property of an object?

Temperature:

• How would we measure temperature?
• Is temperature a property of an object?

Heat:

• Is heat a property of an object?

### Activity: Wrap-up

For this series of questions, the important conclusions students will make should surface in the presentation and class discussion of each small white board after each question is asked. After leaving this activity, students should know that:

• Temperature has the property that energy is spontaneously transfered from hotter objects to colder ones. Temperature is related to the kinetic energy of an object's molecules. As the temperature increases, vibrations in the molecules of an object increase.
• Energy is something that is conserved, and is required to do work. For this course, the ability to do thermodynamic work, or transfer energy via heat, will be of particular importance.
• Heat is energy that is transfered spontaneously from something that is hotter to something that is colder. There are also special cases of irreversible processes where energy-transfer is considered heat even though it doesn't correspond to transfer from something hotter to something colder, but we don't need to bring this up at this stage.
• Entropy is an extensive property of an object (or other system). It can be understood the disorder of a system, but that is a bit hard to quantify. at this stage we will choose to define changes in entropy using an integral of the heat.

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