T 0 °CHeat in 0 kJTime 0 sPressure 0 kPareadyFPS 0

Drag to orbit, wheel or pinch to zoom. The 400 dots are an illustrative picture of the sample (blue-white solid, blue liquid, pale vapour); their motion is not a molecular simulation.

Water Heating Curve: Latent-Heat Plateaus, Pressure-Dependent Boiling and Sublimation

Put heat into a sample of ice at a steady power. The temperature rises, then stops at every phase change while the heat goes into breaking bonds, not into motion. Change the pressure to move the boiling point, or drop below the triple point and watch ice skip the liquid.

Sample and heater

Surroundings

Live readouts

Heating curve: temperature against heat added

Phase diagram of water (log pressure)

Experiment: boiling point against pressure

For each pressure the sample is heated in the simulator until the temperature stops rising at the boiling plateau; the plateau temperature is compared with a steam-table value (IAPWS saturation, quoted from reference tables).

Independent numerical checks

Controls

Drag / one finger: orbit; wheel / pinch: zoom. The thermometer on the stand reads the sample temperature; the hot plate glows with the heater power.
Pressure sets the boiling point (above the triple point) or the sublimation point (below 611.657 Pa).
Heat loss to the room (W per kelvin) can make the temperature stall below the plateau: the heater power must exceed the loss.
Speed multiplies the clock; the heating of 200 g of ice at 1 kW takes about 11 minutes of simulated time.

The science

Sensible heat. Within one phase Q = m c ΔT with c(ice) = 2090, c(liquid) = 4186, c(vapour) = 2010 J/(kg K) (typical values, treated as constant).

Latent heat. A phase change at fixed T absorbs Q = m L: fusion L_f = 334 kJ/kg; vaporisation L_v(T) = 2.493 MJ/kg − 2360 T[°C] (2.257 MJ/kg at 100 °C); sublimation L_s = L_f + L_v(0) + (c_vap − c_ice) T from a Kirchhoff cycle via 0 °C. Boiling a mass of water takes about 6.8 times as much heat as raising it from 0 to 100 °C.

Boiling point against pressure. Saturation pressure follows the Antoine equation log₁₀ p[mmHg] = A − B/(C + T) with A, B, C = 8.07131, 1730.63, 233.426 (1–100 °C) and 8.14019, 1810.94, 244.485 (99–374 °C); inverted for T(p). Over ice, p = 611.21 exp(22.587 T / (273.86 + T)) Pa (Magnus form), inverted for the sublimation temperature. Below the triple-point pressure 611.657 Pa liquid water cannot exist, so heated ice becomes vapour directly.

Heater model. The sample is lumped (uniform temperature): m dh/dt = P − UA (T − T_room) in specific enthalpy h, so temperature is read from h along the staged path (ice, melting, water, boiling or sublimation, vapour). No superheating, supercooling, nucleation delay, dissolved gas or evaporation below the boiling point; the pressure is held fixed (an open vessel, a sealed pressure cooker, a vacuum chamber); the melting point is fixed at 0 °C (pressure effect about −0.0074 K/MPa neglected).

Particle picture. The dots only illustrate the phase: a lattice that shakes more as T rises, a loose liquid, and fast free particles. It is not a molecular dynamics simulation and its speeds are not to scale. Models built with Blender, scene by Three.js.