Heating Curve: Changes of State
Pick a substance, a mass and a heater power, and watch it warm up, melt, boil and keep warming. The temperature graph goes flat while it changes state, because the heater's energy is breaking the bonds between particles rather than speeding them up. Add heat loss to the room to see how it stretches the flat parts or stops the warming.
Preview — sign up free to change the numbers yourself
What you can adjust
- Substance
- 0 – 2
- Mass
- 0.05 – 2 kg
- Heater power
- 10 – 500 W
- Starting temperature
- -120 – 120 °C
- Heat loss to the room
- 0 – 20 W/K
- Heating time
- 1 – 60 min
Each substance melts and boils at its own temperatures and needs its own amount of energy to do it. Stearic acid is a wax-like solid, shown melting only.
How much of the substance there is. Twice the mass needs twice the energy for every step, so everything takes twice as long.
Energy supplied by the heater every second. A bigger heater gets through each step faster.
The temperature the substance starts at. Each substance has its own sensible range (water -40 to 110 °C, ethanol -120 to 90 °C, stearic acid 0 to 120 °C), so a value outside it is moved to the nearest end.
Watts lost for every kelvin the substance is hotter than the 20 °C room. Raise it far enough and heat loss can match the heater, so the temperature stops rising.
How many minutes of heating are shown. The playback is sped up, and the readouts show the real time.
About this simulation
What it shows
A substance is heated at a steady rate while it loses a little heat to the room. A graph of temperature against time is drawn as it melts, boils and warms again, next to a box of particles and bars for their motion energy and bonding energy.
The key idea
Heating does not always raise the temperature. While a substance melts or boils, the energy goes into pulling particles apart (bonding energy) and not into making them move faster (motion energy), so the temperature stays flat until the change is finished.
Try this
Raise Mass from 0.2 kg to 0.4 kg with the other settings unchanged: each flat part of the graph lasts twice as long, because twice as much substance needs twice the energy to change state.
Each state has one fixed heat capacity, and the melting and boiling points are those at normal air pressure. Real substances can supercool or superheat. Stearic acid is shown melting only, and every run stops at a top temperature (200 °C for stearic acid and ethanol, 300 °C for water). Each substance has its own range of starting temperatures, and a value outside it is moved to the nearest end.