How do I read a phase diagram?

Find the temperature on the horizontal axis and the pressure on the vertical axis. The region your point lands in tells you the phase: solid (upper left), liquid (upper middle), or gas (lower right). If the point lies on a boundary line, the two phases on either side coexist. The triple point is where all three lines meet, and the critical point is where the liquid-gas boundary ends.

Is the phase diagram generator free?

Yes. You can generate phase diagrams using the free credits every account starts with. Purchasing any pay-as-you-go credit pack removes the watermark and unlocks higher resolutions. Credits never expire.

What is the triple point and critical point on a phase diagram?

The triple point is the unique pressure and temperature at which solid, liquid, and gas phases all coexist in equilibrium. The critical point is the pressure and temperature above which distinct liquid and gas phases no longer exist and the substance becomes a supercritical fluid. Both are marked as labeled dots on every phase diagram Figviz generates.

Why is the phase diagram of water special?

The phase diagram of water has a negatively sloped fusion curve, meaning higher pressure lowers the melting point. This is the opposite of most substances and occurs because liquid water is denser than ice. To show this correctly in Figviz, include a note about the negative-slope solid-liquid boundary in your prompt.

Can I use it for chemistry class or lab reports?

Yes. Download a high-resolution PNG (up to 4K) and paste it directly into lab reports, slides, or printed worksheets. As an AI tool it is ideal for learning and teaching; verify key values against your textbook before submitting graded work, and diagrams from a paid account can be used in your own teaching materials.

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Phase Diagram Generator Phase Diagrams

Describe a substance and get a clean, labeled phase diagram in seconds. Solid, liquid, and gas regions, triple point, critical point, and all phase boundary lines are drawn and labeled for you. Perfect for chemistry class, lab reports, and lectures.

Last updated: 2026-06-21

✓Pressure-temperature axes✓Triple point and critical point✓All phase boundaries labeled✓Slide and print ready

Phase Diagram Generator

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Phase Diagram Examples

Browse phase diagrams made with Figviz, or generate your own above

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Generic P-T Phase Diagram

A standard pressure-temperature diagram with all three phases, the triple point, the critical point, and all boundary lines labeled.

phase diagrampressure temperaturetriple point

Phase Diagram of Water

The phase diagram of water highlighting its anomalous negative-slope fusion curve, triple point at 0.006 atm, and critical point at 218 atm.

waterphase diagramfusion curve

Phase Diagram of Carbon Dioxide (CO2)

CO2 phase diagram with the triple point at 5.11 atm and the supercritical fluid region above the critical point (73 atm, 31 C).

CO2carbon dioxidesupercritical

Phase Boundaries Labeled Diagram

A phase diagram focused on naming and explaining each boundary line: fusion, vaporization, and sublimation curves.

phase boundariesfusionvaporization

Heating Curve (Temperature vs Heat)

A temperature-vs-heat heating curve showing the flat plateaus at the melting point and boiling point where phase changes occur.

heating curvephase changemelting

Blank Phase Diagram Template

A printable blank phase diagram template with pressure and temperature axes and empty phase regions for students to fill in.

blanktemplateworksheet

What is a phase diagram?

A phase diagram is a graph that maps the state of a substance (solid, liquid, or gas) at every combination of pressure and temperature. The horizontal axis shows temperature and the vertical axis shows pressure. Three curved boundary lines divide the diagram into regions: the fusion curve (solid-liquid boundary), the vaporization curve (liquid-gas boundary), and the sublimation curve (solid-gas boundary). Where all three lines meet is the triple point, the unique pressure and temperature at which all three phases coexist in equilibrium. The endpoint of the vaporization curve is the critical point, above which the substance becomes a supercritical fluid. Figviz draws and labels all of these features from a plain description of the substance, so you get a ready-to-use diagram in seconds.

How to read and make a phase diagram

Identify the substance and any known values for the triple point and critical point.

Note whether the fusion curve slopes positively (most substances) or negatively (water anomaly).

Describe the substance in the prompt, including any specific pressure or temperature coordinates.

Choose a style (classic, colorful, or minimal) and aspect ratio, then generate.

Read the diagram: find your target pressure and temperature, and the region that point falls in tells you the phase.

Refine the prompt if any label or curve needs adjusting, then download at up to 4K resolution.

Key features: triple point, critical point, and phase boundaries

Triple point: the one pressure-temperature coordinate where solid, liquid, and gas phases all coexist. For water this is 0.006 atm and 0.01 C.

Critical point: the end of the vaporization curve. Above this point, pressure and temperature are both too high for separate liquid and gas phases to exist, and the substance becomes a supercritical fluid.

Fusion curve (melting curve): the solid-liquid boundary. Increasing pressure shifts the melting point. For most substances this curve slopes right; for water it slopes left.

Vaporization curve (boiling curve): the liquid-gas boundary. It runs from the triple point to the critical point.

Sublimation curve: the solid-gas boundary. Below the triple point pressure, a substance passes directly from solid to gas without becoming liquid.

The water anomaly and why it matters

Most substances have a phase diagram where the fusion curve slopes to the right, meaning higher pressure raises the melting point. Water is a well-known exception: its fusion curve slopes to the left, which means increasing pressure lowers the melting point. This happens because liquid water is denser than ice, so pressure favors the liquid phase. Practically, this is why ice skates glide: the pressure of the blade can slightly lower the melting point. It is also why water expands when it freezes and why lakes freeze from the top down. When building a phase diagram of water with Figviz, mention the negative-slope fusion curve in your prompt to make sure this anomaly is drawn correctly.

Frequently asked questions

A phase diagram generator is a tool that draws a labeled pressure-temperature chart for a substance automatically. With Figviz you describe the substance and any known values (triple point, critical point, special curve shapes), and the AI produces a clean, labeled diagram with all three phase regions and boundary lines, ready to download in seconds.

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