Latent heat is the energy absorbed or released during a phase change at constant temperature. For melting or freezing it is called the latent heat of fusion (L_f); for boiling or condensing it is the latent heat of vaporization (L_v). The heat is given by Q = mL, where m is mass and L is the specific latent heat in J/kg. For water, L_f = 334 kJ/kg and L_v = 2260 kJ/kg.

Why does temperature stay constant during a phase change?

During a phase change, all the incoming heat energy is used to break intermolecular bonds rather than increase molecular kinetic energy. Since temperature measures average kinetic energy, the temperature stays constant until every molecule has transitioned to the new phase. Only after the phase change is complete does additional heat begin raising the temperature again.

How much energy does it take to turn ice into steam?

To turn 1 kg of ice at 0°C into steam at 100°C requires four steps: (1) melt the ice: Q = mL_f = 334 kJ; (2) heat the water from 0 to 100°C: Q = mcΔT = 4186 × 100 = 418.6 kJ; (3) vaporize the water: Q = mL_v = 2260 kJ; total = 3013 kJ. Notice that vaporization alone takes more than 5 times the energy of all the sensible heating combined!

What is the difference between sensible heat and latent heat?

Sensible heat (Q = mcΔT) changes the temperature of a substance without changing its phase. Latent heat (Q = mL) changes the phase at constant temperature. On a heating curve, sensible heat corresponds to the sloped regions and latent heat corresponds to the horizontal plateaus at the melting and boiling points.

Why is evaporation a cooling process?

Evaporation requires latent heat of vaporization. When water evaporates from your skin, it absorbs heat energy (about 2260 kJ per kg) from your body to break the hydrogen bonds between water molecules. This removes heat and cools the skin. The same principle powers air conditioners, refrigerators, and industrial cooling towers.

Phase Change & Latent Heat Simulator

Q = mcΔT + mL — Solid → Liquid → Gas • Simulate • Explore • Practice • Quiz

Mode

Units

View

📖 User Guide

Presets

Material A

Material B

Heat Input (Q) kJ

Mass (m) kg

Start Temp (T₀) °C

Temp (A)

20.0 °C

Temp (B)

20.0 °C

Phase (A)

Solid

Phase (B)

Solid

Heat Added

500 kJ

Formula

Q = mcΔT + mL

📖 Learning panels

Σ Live equations — step-by-step energy budget for current state

⚖ Phase properties — melt/boil points & latent heats

💡 What-if coach — insights from current values

User Guide — Phase Change & Latent Heat Simulator

1 Overview

The Phase Change Simulator brings the three states of matter to life. Pick a material — water, ethanol, mercury, iron, lead, aluminium, nitrogen, or ammonia — set a starting temperature and 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 gas as you cross each phase boundary, and the heating curve draws the characteristic step pattern with plateaus at the melting and boiling 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 a single-material view and a side-by-side Material A vs Material B comparison, SI/Imperial units, presets, custom materials, and all the usual Simulate/Explore/Practice/Quiz modes.

2 Getting Started

The simulator opens in Simulate mode, Single view, with Water as Material A starting at -20°C (ice). Heat Input is 500 kJ, mass is 1 kg. Press 🔥 Simulate and over roughly twelve seconds you will see: ice warms from −20 to 0 °C (short sloped line); ice melts at 0 °C while the animation shows the lattice collapsing into a liquid (long horizontal plateau); water heats to 100 °C (sloped line); water boils at 100 °C (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 containers side-by-side. Great for comparing how quickly different materials melt, or for showing that mercury and water behave very differently under the same heat input.

3 Simulate Mode

The canvas shows an animated container heated by a gas flame. Particles visualise the current phase: in the solid phase they sit in a lattice and vibrate; in the liquid phase they detach and flow; in the gas phase they scatter above the liquid surface as fast-moving dots and steam wisps rise from the top. A thermometer tracks the instantaneous temperature. When a phase change is in progress, a banner labels which transition is happening (“Melting”, “Boiling”) and the thermometer reading holds steady.

The heating curve in the graph panel shows the full sensible-heat plus latent-heat path. Plateaus at the melting and boiling points are drawn automatically with their labels (“T_m” / “T_b”). In Compare mode, both curves are drawn with distinct colours and a legend appears. The red rolling marker tracks your current heat input position; dots on each curve show where each material is in its phase journey.

4 Explore Mode

Explore has four categories. Phase Basics covers the three states of matter, melting, boiling, sublimation, and phase diagrams. Latent Heat teaches Q = mL, the distinction between fusion and vaporization, why the L values differ, and how latent heat is measured in a calorimetry experiment.

Heating Curve explains how to read the classic temperature-vs-heat graph, why the plateaus are flat, and how their length reflects L×m. Applications covers real-world use cases: refrigeration cycles, sweating and evaporative cooling, steam power, metal casting, cryogenics, weather (why hurricanes get power from evaporated water), and phase-change materials in building insulation.

5 Practice & Quiz

Practice asks randomised problems: energy to melt ice, total energy to turn water into steam, latent heat of fusion from experimental data, final phase of a mixture, and power required to vaporise a given mass in a given time. Enter your numeric answer or click Show Solution for the full step-by-step derivation.

Quiz is five mixed questions per round on definitions (what is latent heat?), values (L_f and L_v for water), reading a heating curve, and applications (why evaporation cools, why steam burns are worse than water burns). You receive a star rating at the end.

6 Features & Power Tools

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, Mercury Thermometer, Liquid Nitrogen, Iron Foundry, Ammonia Refrigerant, Evaporative Cooling, Ice vs Lead, Water vs Mercury.

Custom material: Click + Custom to add your own substance — enter name, specific heats (solid/liquid/gas), latent heats (L_f, L_v), melting and boiling points. Range-checked, SI-internal.

Start temperature: The T₀ slider lets you start the simulation anywhere from −50 to 120 °C (or the equivalent in Imperial). 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 live equations, a full table of phase properties for all materials, and a what-if coach with contextual tips.

Export: CSV for heating-curve data, PNG for the labelled canvas. Also available via right-click.

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

7 Tips & Best Practices

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.
Pair this simulator with the Specific Heat Capacity Simulator (single-phase heating) and the Thermodynamics Cycles Simulator to complete your thermodynamics toolkit.

Understanding Phase Change and Latent Heat

Every time a substance changes between solid, liquid, and gas, an enormous amount of energy flows in or out without any change in temperature. That hidden energy is called latent heat, and it governs everything from the weather to your kettle, from industrial steam turbines to the liquid nitrogen in a cryogenic lab. The simulator above lets you watch the full journey unfold in real time while every joule is tracked on the heating curve.

Latent Heat of Common Substances

Substance	Melting (°C)	Boiling (°C)	L_f (kJ/kg)	L_v (kJ/kg)
Water	0	100	334	2260
Ethanol	−114	78	108	855
Ammonia	−78	−33	332	1371
Mercury	−39	357	11	294
Lead	327	1749	23	871
Aluminium	660	2519	397	10900
Iron	1538	2862	247	6340
Nitrogen	−210	−196	26	199

The Energy Budget: Q = mcΔT + mL

To heat a substance from well below its melting point to well above its boiling point, the total energy is the sum of five separate contributions: (1) sensible heat in the solid phase, m·c_s·ΔT; (2) latent heat of fusion, m·L_f; (3) sensible heat in the liquid phase, m·c_l·ΔT; (4) latent heat of vaporization, m·L_v; (5) sensible heat in the gas phase, m·c_g·ΔT. The graph in the simulator shows all five as alternating slopes and plateaus, with the plateau lengths scaling with m·L.

Why Temperature Stays Constant During a Phase Change

Temperature measures the average kinetic energy of molecules. During melting or boiling, every joule of heat goes into breaking the intermolecular bonds (hydrogen bonds for water, metallic bonds for iron, van der Waals for noble gases) that hold the current phase together. Once all the bonds for a given phase are broken, the molecules can finally move more freely and the temperature starts rising again. This is why ice-water mixtures sit at exactly 0 °C until the last ice cube is gone, and why a rolling boil stays at 100 °C no matter how hard you crank the stove.

Where Latent Heat Matters

Latent heat powers refrigeration and air conditioning (a working fluid evaporates inside the cold coil, absorbing L_v, and condenses outside, releasing it). It drives weather (hurricanes are latent-heat engines — warm ocean water evaporates, releases L_v when it condenses at altitude, and that released energy drives the storm). It enables steam power plants, metal casting foundries, cryogenic medicine, evaporative cooling towers, and phase-change materials that buffer temperature swings in buildings and spacecraft.

Who Uses This Simulator?

This simulator is designed for high-school physics and chemistry students, first-year engineering students, HVAC trainees, and teachers who need a visual way to demonstrate that a phase change is not just a colour swap but a genuine energy transaction. It is also useful for vocational instructors explaining why refrigerants behave the way they do, and for materials-engineering students studying casting, soldering, and heat treatment.

Explore Related Simulators

If you found this phase change simulator helpful, explore our Specific Heat Capacity Simulator, Thermal Expansion Simulator, Heat Transfer Simulator, Refrigeration Cycle Simulator, and Thermodynamics Cycles Simulator for more hands-on practice.