Heating Curve and Phase Change Simulator
Equations in this simulation
| m | Mass of water m (grams) | ||
|---|---|---|---|
| c | specific heat capacity | ice 2.09, liquid water 4.18, steam 2.01 J/(g·K): water needs more heat per degree than almost anything else | |
| ΔT | change in temperature | only while there is a single phase; at a phase change the temperature stays put |
With the current values:
| L_f | latent heat of fusion | 334 J/g: the energy to break the crystal apart without warming it | |
|---|---|---|---|
| L_v | latent heat of vaporization | 2,257 J/g, almost seven times L_f: pulling the molecules right away from each other takes far more than loosening them | |
| Q | heat put in so far | the heater power times the time |
With the current values:
| P | Heater power P (watts; negative cools it) | one watt is one joule per second | |
|---|---|---|---|
| t | time for each stage | the plateaus are long because the latent heats are large |
With the current values:
How to use the heating curve simulator
- Set the mass of water, its starting temperature and the heater power. It starts as ice: the molecules sit in a crystal, each shaking about its place, and they shake harder as the temperature rises.
- At 0 °C the temperature stops while the ice melts: the heat goes into breaking the crystal apart, and molecules break loose one by one into the liquid. At 100 °C it stops again while the water boils and molecules fly off as steam. The chart draws the heating curve against the heat put in, over the whole curve in gray, with its two flat steps.
- Turn the power negative to take heat out and run the curve backward, freezing and condensing. The equations add up the heat for each stage from the specific and latent heats; the Specific Heat Calculator works out Q = mcΔT for any substance.
Frequently asked questions
Why does the temperature stay the same while ice melts?
Because all the heat goes into breaking the bonds that hold the molecules in the crystal, not into making them move faster. Temperature measures the average kinetic energy of the molecules, which does not change until the last of the ice has melted. The heat absorbed is the latent heat of fusion, 334 J for every gram.
What is latent heat?
The energy a substance takes in or gives out when it changes phase at a constant temperature. For water the latent heat of fusion (melting) is 334 J/g and of vaporization (boiling) 2,257 J/g. The same amounts come back out on freezing and condensing, which is why steam scalds far worse than boiling water at the same temperature.
Why does boiling take so much longer than melting?
Because the latent heat of vaporization is almost seven times that of fusion. Melting only loosens the molecules so they can slide past each other; boiling has to pull them completely apart against the attraction between them. Bringing 100 g of water from 0 °C to the boil takes 42 kJ; boiling it all away takes another 226 kJ.
How do I calculate the heat for a heating curve?
Add up each stage: warming the ice (m × 2.09 × ΔT), melting it (m × 334), warming the water (m × 4.18 × ΔT), boiling it (m × 2,257) and warming the steam (m × 2.01 × ΔT), with m in grams. Divide by the heater power in watts to get the time in seconds; the equations under the picture do this for your settings.
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.