Hidden Heat
Why doesn't adding thermal energy to matter ALWAYS increase its temperature?
Let's find out!
Elliotte, an eighth grade science student, placed a thermometer into boiling water, and the thermometer read 100*C. Elliotte increased the heat on the hot plate from medium to high. To his amazement and confusion, the temperature of the water didn't change! It remained a constant 100*C, but the water boiled faster. What in the world was happening here?!
Continue
Predict and describe changes in particle motion, temperature and state of a pure substance when thermal energy is added or removed.
Learning Objective
Title
Use this side to give more information about a topic.
Subtitle
Continue
'Yeah, I cranked up the heat on this pan of boiling water, but the water didn't get any hotter. It's like the heat is hiding or something...'
--Elliotte
Continue
Elliotte re-watched this video his teacher had shared in class:
Continue
increasing energy
And he carefully studied this model of the three main states of matter:
gas
liquid
solid
Liquid
Gas
Solid
Molecules stay close together but can flow easily around each other.
Molecules fly in all directions at great speeds, colliding with each other and the walls of their container.
Molecules are arranged in regular, repeating patterns. They vibrate in place.
Continue
Continue
What is the melting point of water?
What is the boiling point of water?
Water boils, or changes from a liquid to a gas, at 100 degrees Celsius.
Water melts, or changes from a solid to a liquid, at 0 degrees Celsius.
Title
Title
Use this side to give more information about a topic.
Use this side to give more information about a topic.
Subtitle
Subtitle
Continue
'OK, I know that water's molecules move faster and faster when heat is added. But why did the water stay at the boiling point of 100*C even though I kept adding heat? Why didn't its temperature increase while it was boiling?
Continue
Here's a video he found:
So the hidden heat actually has a name: latent heat. I'll research that term and see what else I can find.
Continue
Elliotte found this:
What happens to the temperature of the water during the phase changes?
Continue
Continue
Continue
Wow! So, during a phase change, added thermal energy is used to break the bonds between the water molecules so they can change from a solid to a liquid or a liquid to a gas, not to increase the temperature of the water!
Continue
Elliotte decided to make a scientific model that explains this "hidden heat."
He started with this graph showing that the temperature of water remains constant when ice melts and again when water boils. Flip through the images to see what Elliotte added to the graph, step by step, to make it a better scientific model.
Continue
Thanks, folks!
Please complete the Microsoft Form.
Sources used:
- Slide 3 Learning Objective: PA STEELS standard 3.2.6-8.B Physical Science: Structure and Properties of Matter
- Elliotte's image on various slides: Getty Images/iStockphoto. Creator: nadia_bormotova
- Slide 5 video Phase Changes: https://witf.pbslearningmedia.org/resource/phases-of-matter-phase-changes-animation/unc-tv-science/
- Slide 6 phase diagrams: https://www.britannica.com/science/phase-state-of-matter
- Slide 8 images:
- melting ice: https://www.chemistryviews.org/details/news/10700782/Ice_Melting_under_Pressure/
- boiling water: https://www.dummies.com/article/home-auto-hobbies/food-drink/cooking-baking/general-cooking-baking/how-to-boil-water-206775/
- Slide 10 video Latent Heat Explained: https://www.youtube.com/shorts/i-D6OjM8ieY
- Slide 11 Screencast video made from Javalab simulation: https://javalab.org/en/boiling_point_en/
- Slide 15 scientific model:
- temperature graph: https://javalab.org/en/boiling_point_en/
- molecular motion: https://www.britannica.com/science/phase-state-of-matter
The student's next steps:
Elliotte decided to look back at his science notes about states of matter. Maybe the answer was somewhere in there.
The student's next steps:
Elliotte decided to do some research online, hoping to find a video that might explain what was going on.
Hidden Heat
Margaret Yeater
Created on September 29, 2025
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Transcript
Hidden Heat
Why doesn't adding thermal energy to matter ALWAYS increase its temperature?
Let's find out!
Elliotte, an eighth grade science student, placed a thermometer into boiling water, and the thermometer read 100*C. Elliotte increased the heat on the hot plate from medium to high. To his amazement and confusion, the temperature of the water didn't change! It remained a constant 100*C, but the water boiled faster. What in the world was happening here?!
Continue
Predict and describe changes in particle motion, temperature and state of a pure substance when thermal energy is added or removed.
Learning Objective
Title
Use this side to give more information about a topic.
Subtitle
Continue
'Yeah, I cranked up the heat on this pan of boiling water, but the water didn't get any hotter. It's like the heat is hiding or something...'
--Elliotte
Continue
Elliotte re-watched this video his teacher had shared in class:
Continue
increasing energy
And he carefully studied this model of the three main states of matter:
gas
liquid
solid
Liquid
Gas
Solid
Molecules stay close together but can flow easily around each other.
Molecules fly in all directions at great speeds, colliding with each other and the walls of their container.
Molecules are arranged in regular, repeating patterns. They vibrate in place.
Continue
Continue
What is the melting point of water?
What is the boiling point of water?
Water boils, or changes from a liquid to a gas, at 100 degrees Celsius.
Water melts, or changes from a solid to a liquid, at 0 degrees Celsius.
Title
Title
Use this side to give more information about a topic.
Use this side to give more information about a topic.
Subtitle
Subtitle
Continue
'OK, I know that water's molecules move faster and faster when heat is added. But why did the water stay at the boiling point of 100*C even though I kept adding heat? Why didn't its temperature increase while it was boiling?
Continue
Here's a video he found:
So the hidden heat actually has a name: latent heat. I'll research that term and see what else I can find.
Continue
Elliotte found this:
What happens to the temperature of the water during the phase changes?
Continue
Continue
Continue
Wow! So, during a phase change, added thermal energy is used to break the bonds between the water molecules so they can change from a solid to a liquid or a liquid to a gas, not to increase the temperature of the water!
Continue
Elliotte decided to make a scientific model that explains this "hidden heat."
He started with this graph showing that the temperature of water remains constant when ice melts and again when water boils. Flip through the images to see what Elliotte added to the graph, step by step, to make it a better scientific model.
Continue
Thanks, folks!
Please complete the Microsoft Form.
Sources used:
The student's next steps:
Elliotte decided to look back at his science notes about states of matter. Maybe the answer was somewhere in there.
The student's next steps:
Elliotte decided to do some research online, hoping to find a video that might explain what was going on.