Heating and cooling curves
Heating and Cooling Curve graphs a substance’s temperature as it is heated or cooled steadily, through its melting and boiling points. Each phase warms or cools in a sloped segment and each phase change is a flat plateau, and the curve has only the segments its starting and ending temperatures pass through. Pick water, ethanol, acetone, mercury, sodium chloride or a made-up Substance X, or type your own melting and boiling points. Segments are schematic, in tidy textbook proportions you can change, or worked out to scale from the substance’s specific heats and enthalpies of fusion and vaporization for the mass and heating rate you choose, with the heat each segment takes listed for your answer key.
Teachers use it for questions on phase changes, heat and temperature: what is happening between B and C, why the temperature doesn’t change while ice melts, which plateau is longer and why. Letter the corners A to F, label each segment with its state or phase change or leave a blank line for students. The dashed lines from the plateaus to the temperature axis have the melting and boiling points written by them, so they can be read on any axis; write m.p. and b.p. instead, or leave blank lines for students.
What you can set
- Heating or cooling, and the starting and ending temperatures
- The substance: water, ethanol, acetone, mercury, sodium chloride, a made-up Substance X, or your own melting and boiling points
- Segment lengths schematic (typed) or to scale, from the mass and the substance’s specific heats and enthalpies of fusion and vaporization (typed for your own substance)
- Time or the heat added or removed along the x-axis, at a heating rate you choose
- Letters at the corners, segment labels (states, the phase change, or blank lines), dashed lines at the plateaus with the temperatures (the default), m.p. and b.p., blank lines or nothing by the axis, and supercooling on a cooling curve
- The curve’s color, the chart and axis titles (or blank lines), the axis ranges and numbering, gridlines, and label size
Copying, printing and sharing
Copy the figure straight into a test, worksheet or slide, or download it as a PNG or SVG. Printing the page prints
just the figure. Share link copies the page’s address with your settings in it, so anyone who opens it sees this
exact figure, and presets save settings you use often in your browser. It’s free, with no sign-up.
Frequently asked questions
Why is the temperature flat during a phase change?
While a substance melts or boils, the heat added goes into pulling its particles apart (raising their potential energy) instead of making them move faster, so the temperature stays at the melting or boiling point until the change is complete. On a cooling curve the same heat comes back out while it freezes or condenses.
Why is the boiling plateau longer than the melting plateau?
Boiling separates the particles completely, which takes much more energy than loosening them into a liquid. For water the enthalpy of vaporization, 40.67 kJ/mol, is about 6.8 times the enthalpy of fusion, 6.01 kJ/mol, so drawn to scale its boiling plateau is about 6.8 times as long.
Can I make a curve for a substance other than water?
Yes. Pick ethanol, acetone, mercury, sodium chloride or a made-up Substance X, or choose Custom and type its melting and boiling points. For your own substance drawn to scale, type its specific heats, enthalpies of fusion and vaporization and molar mass too.
Is the curve drawn to scale?
Only if you want it to be. Schematic, the default, draws the segments in tidy textbook proportions, which you can change. To scale works out how long each takes from q = m·c·ΔT and q = n·ΔH, for the mass and heating rate you choose. The specific heats are each phase’s near the temperatures its segment covers where that’s known, otherwise at 25 °C, so a curve to scale is close but not exact.
Can I show supercooling?
Yes, on a cooling curve that freezes: tick Supercooled and type how far below the freezing point the liquid cools before it starts to freeze. The curve dips below the freezing point and climbs back to it, and the rest of the curve stays where it was.
Chemistry Figures Heating and Cooling Curve