Phase Change & Latent Heat Simulator

The Phase Change Simulator brings the three states of matter to life. Pick one of eleven materials — water, ethanol, ammonia, carbon dioxide, mercury, lead, aluminium, iron, copper, nitrogen or oxygen — set a starting temperature, an ambient pressure and a heat input, and watch the substance travel through the full solid → liquid → gas journey. Animated particles switch from rigid lattice, to flowing liquid, to fast-moving vapour as you cross each phase boundary, and the heating curve draws the characteristic step pattern with plateaus at the transition points.

Unlike the specific-heat simulator (where temperature rises linearly), this tool uses the full energy budget Q = mcΔT + mL. During a phase change the temperature stops rising even as heat keeps flowing, because every joule goes into breaking intermolecular bonds. The tool supports single and side-by-side Material A vs B views, a Heat / Cool direction toggle for cooling curves, a pressure control that moves the boiling point and can switch the substance into sublimation, a heater power control that turns every energy figure into a time, SI/Imperial units, presets, custom materials, and the usual Simulate/Explore/Practice/Quiz modes.

The simulator opens in Simulate mode, Single view, with Water as Material A starting at −20°C (ice), 1 kg, at 1.013 bar with a 1500 W heater. The Heat Input slider is auto-fitted to whatever is needed to carry the sample through every transition plus a short tail, and it re-fits itself whenever you change material, mass, start temperature, pressure or direction — so you can always reach the plateaus.

Press 🔥 Heat and over roughly twelve seconds you will see: ice warms from −20 to 0 °C (short sloped line); ice melts at 0 °C while a shrinking crystalline block gives way to liquid (long horizontal plateau); water heats to 100 °C (sloped line); water boils (very long plateau — vaporization takes 6.8× the fusion energy); steam rises above 100 °C (steep line, because steam has a low specific heat).

Switch to Compare A vs B in the View pill to show two beakers side-by-side — useful for showing that mercury and water behave completely differently under the same heat input.

The canvas shows a glass beaker on a bench, heated by a Bunsen flame (or chilled by a frosted cooling plate when the direction is set to Cool). What is inside the beaker is drawn directly from the computed phase fractions, so the picture can never disagree with the numbers: a solid appears as a faceted crystalline block, a liquid as a graded column with a meniscus, and vapour as wisps leaving the neck. During a melting plateau you see the block shrink while the liquid rises — the two phases genuinely coexist at T_m. Ice is drawn floating, because water is the anomaly whose solid is less dense than its liquid; every other material’s solid sinks.

Particles visualise the molecular picture: locked in a vibrating lattice in the solid, detached and flowing in the liquid, and escaping upward through the neck as vapour. A thermometer tracks the instantaneous reading, and a badge above the beaker names the current state or transition.

The graph panel plots the full sensible-plus-latent path. Latent segments are drawn in their own transition colour (amber fusion, orange vaporization, pink sublimation, and the cooler colours for the reverse transitions), and dashed reference lines mark T_m, T_b or T_sub at the pressure you have set. Below the graph, one banner per transition shows Q = mL with a live progress bar and, when a heater power is set, how long that plateau lasts.

Explore has four categories. Phase Basics covers the three states of matter, melting and freezing, boiling and condensing, sublimation and deposition, and the triple point and phase diagram. Latent Heat teaches Q = mL, the distinction between fusion and vaporization, why L_v is so much larger than L_f, evaporative cooling, and how a latent heat is actually measured in the lab with L = Pt/m.

Curves & Pressure explains how to read the temperature-vs-heat graph, why the plateaus are flat, how their length reflects m×L, what the cooling curve looks like, how the slopes relate to 1/(mc), and how Clausius–Clapeyron sets the boiling point at any pressure. Applications covers refrigeration cycles, weather (why hurricanes are latent-heat engines), metal casting, freeze-drying, and phase-change materials in buildings. Every concept card carries a worked numeric example.

Practice asks randomised problems drawn from fourteen generators: energy to melt or vaporize a given mass, the full ice-to-steam budget, reading L_f off a plateau, evaporative cooling of the human body, power required to vaporise a mass in a given time, how long a boiling plateau lasts at a given heater power, energy that must be removed to freeze water, calorimetry (L = Pt/m), and estimating a boiling point from pressure with Clausius–Clapeyron. Enter your numeric answer or click Show Solution for the full step-by-step derivation.

Quiz is five questions per round drawn from a pool of twenty-two, covering definitions, the values of L_f and L_v, reading a heating curve, pressure effects (Everest, pressure cookers), sublimation and the triple point, freeze-drying, and calorimetry. You receive a star rating and a per-question review at the end.

Single / Compare view: The View pill at the top flips between a single material (centre-stage) and a side-by-side A vs B comparison.

Units (SI / Imperial): Every readout, slider label, axis, and modal step converts between SI (kJ, kg, °C, J/(kg·K), kJ/kg) and Imperial (BTU, lb, °F). Calculations stay in SI internally for accuracy.

Presets: One-click scenarios along the top — Ice to Steam, Melting Lead, Boiling Ethanol, Dry Ice Sublimes, Pressure Cooker, Boiling on Everest, Freeze-Drying, Liquid Nitrogen, Freezing Water, Condensing Steam, Iron Foundry, Ice vs Lead, Water vs Mercury.

Custom material: Click + Custom to add your own substance — name, melting and boiling points, molar mass, the three specific heats, and both latent heats. Every field is range-checked and stored in SI. Molar mass is required because the pressure model needs it.

Direction (Heat / Cool): Switch to Cool and the burner is replaced by a frosted chilling plate, the x-axis becomes “heat removed”, and the plateaus become condensation and freezing — same temperatures, same energies, but released instead of absorbed. The start temperature jumps to the far end of the curve automatically so the reverse run has somewhere to go.

Pressure: A logarithmic slider from 0.001 to 20 bar. The boiling point is recomputed from the Clausius–Clapeyron relation at every step, and the readout card shows the result. Drop below a material’s triple-point pressure and the liquid field closes entirely: the simulator switches to a single sublimation plateau using L_sub. Try 2 bar for a pressure cooker (about 120 °C), 0.337 bar for the summit of Everest (about 71 °C), or 0.004 bar to freeze-dry.

Heater power: 50 W to 20 kW. Every energy figure gains a companion time via t = Q/P, including the duration of each individual plateau. This is the quantity you would time with a stopwatch in a calorimetry experiment, and inverting it (L = Pt/m) is how latent heat is measured.

Start temperature: The T₀ slider spans the range that is meaningful for the current material and pressure — from well below the melting point to well above the boiling point — and rescales automatically when you change either. Perfect for demonstrating “what if we start with liquid water instead of ice?”

Canvas toggles: Hide/show Flames, Particles, Graph, Equation, or enable Keep Traces to layer multiple runs onto the same chart for comparison.

Show Calculations (🔢): Opens a step-by-step modal that walks through sensible heating, melting, liquid heating, vaporization, and final-state identification with all substitutions.

Learning panels: Three collapsible cards below the readouts show the live energy budget segment by segment (with cumulative energy and elapsed time), a full property table for every material — molar mass, T_m, T_b, L_f, L_v, the L_v/L_f ratio and all three specific heats — and a what-if coach that comments on your current pressure, power and phase state.

Export: CSV of the curve sampled at 100 points, including elapsed time and phase name at each step, with the material, pressure, heater power and transition temperatures in the header. PNG exports the labelled canvas at full device resolution. Both are also on the right-click menu.

Undo / Redo: Ctrl+Z and Ctrl+Shift+Z step through recent changes.

• The longest plateau on a water heating curve is vaporization, not melting — L_v (2260 kJ/kg) is about 6.8× L_f (334 kJ/kg). This is why a kettle takes much longer to boil dry than to reach boiling.
• Steam at 100 °C contains far more energy than water at 100 °C because of the latent heat released when it condenses on your skin — that is why steam burns are so dangerous.
• Evaporation cools because the escaping molecules carry away L_v joules per kilogram. This is the physics behind sweating, clay pots that cool water, and every air conditioner ever built.
• The specific heats of the solid and liquid phase are often different: ice c = 2090 J/(kg·K), liquid water c = 4186 J/(kg·K), steam c ≈ 2010 J/(kg·K). The simulator uses the correct value for each region of the curve.
• For mercury and most pure metals, the liquid and solid specific heats are nearly equal, so the sloped sections look symmetric — only the plateau lengths carry information about L_f and L_v.
• Boiling point is a property of the pressure, not of the liquid alone. Slide the pressure down and watch T_b fall while T_m stays put — the fusion line on a P–T diagram is almost vertical, so melting points barely respond to pressure.
• Below the triple-point pressure there is no liquid at all. Water’s triple point is 6.117 mbar, so ice sublimes below that; carbon dioxide’s is 5.18 bar, which is why dry ice sublimes at ordinary atmospheric pressure and never puddles.
• Set a heater power and each plateau reports its own duration. Reading L off a stopwatch this way (L = Pt/m) is exactly the standard school calorimetry experiment.
• The boiling-point figures come from the Clausius–Clapeyron relation with a constant latent heat. Checked against steam tables the error is under about 1 °C between 0.3 and 10 bar, growing to roughly 2 °C at 0.1 bar and near the critical point, where the constant-L assumption breaks down.
• Pair this simulator with the Specific Heat Capacity Simulator (single-phase heating) and the Thermodynamics Cycles Simulator to complete your thermodynamics toolkit.