1386: "Water Can Boil and Freeze at the Same Time"
Interesting Things with JC #1386: "Water Can Boil and Freeze at the Same Time" – Fire and ice at once? At the triple point, water boils, freezes, and steams in a single breath. It's a scientific paradox that defies expectation.
Curriculum - Episode Anchor
Episode Title: Water Can Boil and Freeze at the Same Time
Episode Number: 1386
Host: JC
Audience: Grades 9–12, college intro, homeschool, lifelong learners
Subject Area: Physics, Chemistry, Science Literacy
Lesson Overview
Learning Objectives:
Define the triple point of water and its specific conditions.
Compare boiling, freezing, and melting points under normal and reduced pressure.
Analyze how scientists demonstrate the triple point in a laboratory setting.
Explain the significance of the triple point in defining the Kelvin temperature scale.
Key Vocabulary
Triple Point (ˈtrɪ-pəl pɔɪnt) — The unique set of conditions where water exists as solid, liquid, and vapor at the same time.
Pascal (ˈpæs-kəl) — A unit of pressure; at the triple point of water, pressure is 611 pascals.
Kelvin Scale (ˈkɛl-vən skeɪl) — The scientific temperature scale defined by the triple point of water.
Phase Change (feɪz ʧeɪndʒ) — A transformation between states of matter, such as freezing, melting, or boiling.
Vacuum Pump (ˈvæk.juːm pʌmp) — A device that removes air to lower pressure, used to demonstrate water’s triple point in a lab.
Narrative Core
Open: A kettle boils while ice freezes, introducing the paradox of opposite states.
Info: Normally, boiling and freezing are understood as separate and opposing processes.
Details: At the triple point—0°C and 611 pascals—water can exist as ice, liquid, and vapor simultaneously.
Reflection: This scientific reality also offers a metaphor—extremes can coexist in balance.
Closing: These are interesting things, with JC.
A clear glass filled with water shows both boiling bubbles rising to the surface and ice forming at the bottom. Steam lifts into the air above, illustrating water boiling and freezing at the same time. White text at the top reads: “Interesting Things with JC #1386 – Water Can Boil and Freeze at the Same Time.”
Transcript
Picture this. A kettle boils on the stove, steam rising into the air. In the freezer, ice trays sit frozen stiff. We think of boiling and freezing as opposites—but under rare conditions, water can do both at the very same time.
This is called the triple point. It happens only at 32 degrees Fahrenheit (0 degrees Celsius) and under a pressure of just 611 pascals, compared to the 101,325 we live in at sea level. At that razor-thin balance, water exists as ice, liquid, and vapor all at once.
In the lab, scientists show it with a sealed glass tube of pure water. A pump pulls the air out, lowering the pressure until the water boils—even though it’s cold. As it bubbles, the heat loss is so great that the rest freezes into ice. You can literally watch boiling and freezing side by side, in the same container.
It isn’t just a lab trick. The triple point is so exact that scientists use it to define the Kelvin temperature scale—the universal yardstick for measuring heat and cold. No matter where you are, those conditions always bring the same result.
Boiling and freezing look like opposites, yet in balance, they can exist together. In science, that’s a law of nature. In life, it’s a reminder—two extremes don’t always have to fight. Sometimes, when the pressure is just right, they can share the same space and still hold their form.
These are interesting things, with JC.
Student Worksheet
Define the triple point of water in your own words.
How does pressure influence boiling and freezing?
Why do scientists use the triple point to define the Kelvin scale?
Describe the laboratory setup used to demonstrate the triple point.
Reflect: What lesson about balance in life can be drawn from the triple point?
Teacher Guide
Estimated Time: 1–2 class periods (45–90 minutes)
Pre-Teaching Vocabulary Strategy: Use visuals of phase diagrams, show pressure differences in pascals vs. atmospheric pressure.
Anticipated Misconceptions: Students may think water can reach the triple point at normal atmospheric pressure; clarify that conditions must be exact.
Discussion Prompts:
Why is the triple point so rare in nature?
How does the Kelvin scale differ from Celsius and Fahrenheit?
Differentiation Strategies:
ESL: Provide bilingual glossaries for key terms.
IEP: Use tactile models of molecules in solid, liquid, and gas states.
Gifted: Ask students to research other substances’ triple points.
Extension Activities: Students design a phase diagram poster; experiment with dry ice sublimation as a comparison.
Cross-Curricular Connections:
Physics: Thermodynamics and pressure.
Chemistry: Molecular motion during phase changes.
Philosophy: Balance and paradox in scientific and human systems.
Quiz
At what pressure does the triple point of water occur?
A. 101,325 Pa
B. 611 Pa
C. 0 Pa
D. 32 Pa
Answer: BWhat temperature corresponds to the triple point of water?
A. 100°C
B. 25°C
C. 0°C
D. -32°C
Answer: CWhy does water freeze during the boiling demonstration at low pressure?
A. Lack of oxygen
B. Heat loss from evaporation
C. Ice crystals form automatically
D. The glass tube cools rapidly
Answer: BWhat scientific measurement scale is defined by the triple point of water?
A. Celsius
B. Fahrenheit
C. Kelvin
D. Rankine
Answer: CWhat is unique about the triple point?
A. Water cannot exist at that state
B. Only vapor forms
C. Solid, liquid, and vapor coexist
D. It happens at room temperature
Answer: C
Assessment
Explain why the triple point is a critical benchmark in thermodynamics.
Compare the triple point of water with the freezing and boiling points under normal atmospheric pressure.
3–2–1 Rubric
3: Accurate, complete, thoughtful, supported with details.
2: Partial answer with some missing detail.
1: Inaccurate, vague, or unsupported answer.
Standards Alignment
NGSS HS-PS1-4: Develop models to illustrate changes in molecular motion during phase changes.
NGSS HS-PS3-4: Investigate how changes in pressure and energy affect states of matter.
CCSS.ELA-LITERACY.RST.9-10.3: Follow complex procedures in a science text to conduct experiments.
CCSS.ELA-LITERACY.RST.11-12.2: Determine central ideas in scientific explanations.
C3.D1.5.9-12: Evaluate scientific evidence in real-world and laboratory contexts.
ISTE 3b: Students evaluate data to understand conditions of scientific phenomena.
UK National Curriculum (Physics, Key Stage 4): Understand pressure, temperature, and changes of state.
IB DP Physics (Topic 3: Thermal Physics): State and explain the concept of the triple point.
Cambridge IGCSE Physics (0625, Section 4): Describe and explain phase changes with reference to energy and pressure.
Show Notes
In this episode of Interesting Things with JC, listeners explore the fascinating concept of the triple point of water, a rare state where ice, liquid water, and vapor coexist. The discussion explains how the balance of temperature and pressure creates this phenomenon, why scientists use it to define the Kelvin scale, and how it can be demonstrated in the lab. For classrooms, this episode provides a gateway into thermodynamics, molecular behavior, and the precision of scientific measurement. Beyond science, the story offers a reminder of how extremes can coexist in balance—a concept with both physical and philosophical meaning.
References
National Institute of Standards and Technology. (n.d.). Triple-point cells. Retrieved from https://www.nist.gov/video/triple-point-cell
Cuddon Freeze-Dry. (2019, September 10). What is triple point? Retrieved from https://info.cuddonfreezedry.com/blog/what-is-triple-point
Fluke Calibration. (n.d.). What is the triple point of water? Retrieved from https://www.fluke.com/en-us/learn/blog/calibration/what-is-triple-point-of-water
