Phase Diagram of Water
Lesson notes
Overview
Temperature and pressure decide whether water is solid, liquid or vapour. This topic is rated intermediate and is number 190 of 227 in Physics. Builds on the basics with relationships, methods and trade-offs.
What you are seeing
The panel above shows the steps of a process, laid out in order. Click a step to see what happens next. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
A phase diagram maps whether water is solid, liquid or gas at each temperature and pressure. The lines mark where two phases coexist, and they meet at the triple point at 0.01 °C and 0.006 atm, where all three exist together. Unusually, the melting line of ice slopes backward, so pressure can melt ice. Above the critical point, 374 °C and 218 atm, liquid and gas cannot be distinguished. Freeze drying and pressure cookers exploit different parts of the diagram.
Reading the relationship
The expression "triple point 0.01 °C" is a compact summary of the idea. It uses the symbols t, r, i, p, l, e; name what each one stands for before you start. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.
Try this
Predict the outcome first, then test extreme slider values to find where the pattern changes or breaks.
Common pitfalls
Check units and directions first. Many mistakes come from mixing up a scalar with a vector, or from using a formula outside the conditions where it holds.
How it connects
It builds on “The Laws of Thermodynamics”, the topic before it in Physics. Once you are comfortable, continue with “How a Heat Pump Works”.
Why it matters
Physics explains how the world moves, heats, shines and interacts, and the same principles power technology around you.
Where you might use it
- Revising “Phase Diagram of Water” before a class, exam or certification
- Designing vehicles, bridges and devices where motion, forces or waves must be predicted
- Understanding how sensors, lasers and communication links actually work
- Explaining everyday phenomena such as sound, light, heat and orbits
Frequently asked questions
What is Phase Diagram of Water?
Temperature and pressure decide whether water is solid, liquid or vapour. It is an intermediate topic in Physics.
How do I use the Phase Diagram of Water simulation?
The panel at the top shows the steps of a process, laid out in order. Click a step to see what happens next. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression triple point 0.01 °C packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Builds on the basics with relationships, methods and trade-offs. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “The Laws of Thermodynamics”, the previous topic in Physics. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.