TutorForAll

Heating ice: where does the energy go?

Years 5–8Stage 3 to Stage 4Run it

Everything is made of tiny particles that are always moving. Heating gives the particles energy.

Demonstration: a simplified modelNot to scale1 · Ice

A model of 10 g of water, drawn as particles, in a cylinder whose lid slides freely, on a heater that gives it energy at a steady rate. State: Solid (ice). The particles: In fixed places in a regular pattern, each vibrating. A thermometer stands in it and reads −20 °C. The thermometer: Rising. Beside it, a graph of the temperature against time shows the line so far, to 0.00 minutes.

Safety: steam and boiling water scald. Never heat water in a closed container.

Ice at 20 °C below zero. Its particles sit in fixed places in a regular pattern, each vibrating on the spot.

  1. Thermometer
  2. Sliding lid
  3. Heater

Key Circles: water particles, drawn far larger than real ones. In steam the particles have only empty space around them. Short arrows: the way some particles of steam are moving. Dashed arrows: energy moving from the heater into the water. Dashed arrows: energy moving out of the water into the cooler. Red column: the thermometer's reading. Solid red line: the temperature, as time goes on. Dashed grey line: the same water with the medium setting, to compare.

The model could not start here. The figure, the steps and the table on this page still show the idea; reload the page to try again.

The idea, step by step

Not to scale

  1. A model of 10 g of water, drawn as particles, in a cylinder whose lid slides freely, on a heater that gives it energy at a steady rate. State: Melting (ice and water together). The particles: Some still in fixed places, some breaking free. A thermometer stands in it and reads 0 °C. The thermometer: Holding steady. Beside it, a graph of the temperature against time shows the line so far, to 0.70 minutes.
    2 · MeltingWhile the ice melts, the thermometer holds at 0 °C, though the heater keeps going. Particles break free of their places; none melts.1 Thermometer · 2 Sliding lid · 3 Heater
  2. A model of 10 g of water, drawn as particles, in a cylinder whose lid slides freely, on a heater that gives it energy at a steady rate. State: Liquid (water). The particles: Close together, sliding past each other. A thermometer stands in it and reads 54 °C. The thermometer: Rising. Beside it, a graph of the temperature against time shows the line so far, to 2.00 minutes.
    3 · Water warmsAll the ice has melted. The particles touch but slide past each other, and move faster as the water warms.1 Thermometer · 2 Sliding lid · 3 Heater
  3. A model of 10 g of water, drawn as particles, in a cylinder whose lid slides freely, on a heater that gives it energy at a steady rate. State: Boiling (water and steam together). The particles: Close together in the water, far apart in the steam. A thermometer stands in it and reads 100 °C. The thermometer: Holding steady. Beside it, a graph of the temperature against time shows the line so far, to 6.00 minutes.
    4 · BoilingAt 100 °C the water boils. Its particles leave as steam and move far apart. The space between them holds no air.1 Thermometer · 2 Sliding lid · 3 Heater
  4. A model of 10 g of water, drawn as particles, in a cylinder whose lid slides freely, on a heater that gives it energy at a steady rate. State: Boiling (water and steam together). The particles: Close together in the water, far apart in the steam. A thermometer stands in it and reads 100 °C. The thermometer: Holding steady. Beside it, a graph of the temperature against time shows the line so far, to 3.00 minutes.
    5 · Stronger heaterThe high setting brings the water to the boil sooner and boils it away faster, but it still boils at 100 °C.1 Thermometer · 2 Sliding lid · 3 Heater
  5. A model of 10 g of water, drawn as particles, in a cylinder whose lid slides freely, on a heater that gives it energy at a steady rate. State: Gas (steam). The particles: Far apart, moving freely. A thermometer stands in it and reads 120 °C. The thermometer: Rising. Beside it, a graph of the temperature against time shows the line so far, to 10.30 minutes.
    6 · All steamAll steam, at 120 °C. Its particles move faster, so the steam spreads and the lid rises. They stay the same size.1 Thermometer · 2 Sliding lid · 3 Heater
  6. A model of 10 g of water, drawn as particles, in a cylinder whose lid slides freely, on a cooler that takes energy from it at a steady rate. State: Freezing (water and ice together). The particles: Some sliding past each other, some settling into fixed places. A thermometer stands in it and reads 0 °C. The thermometer: Holding steady. Beside it, a graph of the temperature against time shows the line so far, to 9.61 minutes.
    7 · CoolingCooling steam: it condenses at 100 °C and freezes at 0 °C, holding steady each time while energy keeps leaving.1 Thermometer · 2 Sliding lid · 3 Cooler

Each moment a change of state starts or ends, and now

MomentTime since the start (min)Temperature (°C)State from then on
Start0.00-20Solid (ice)
Ice starts to melt0.140Melting (ice and water together)
The last ice melts1.250Liquid (water)
Water starts to boil2.65100Boiling (water and steam together)
The last water boils10.17100Gas (steam)
End: all steam10.30120Gas (steam)

Try it in the Lab

Practicals with real materials, each with its safety card.

With a learner

Three questions to ask

  1. What do the particles in the ice do before it starts to melt?
  2. Why does the thermometer stop rising while the ice melts, even though the heater is still on?
  3. Is there anything in the space between the particles of steam?

What to expect

Many learners expect the temperature to keep rising the whole time, and think steam's particles are bigger than water's.

What to try next

Open a practical in Try it in the Lab, above, to melt ice while reading a thermometer every minute, or to watch stearic acid freeze.

About this model

What is simplified

  • The model heats 10 g of water in a cylinder whose lid slides freely, so the water stays at normal atmospheric pressure. In a box with a fixed lid, the pressure would rise as the water boiled, and it would boil hotter.
  • The particles are drawn far larger and far fewer than real ones, each a circle of one size. Each stands for one water particle, a molecule.
  • The solid is drawn as a simple grid. In real ice the particles are held in an open pattern of hexagons, so ice takes up more space than the water it melts into, and floats on it. The drawing gives the solid and the liquid the same space.
  • Steam takes up about 1600 times the space of the water it came from. The drawing lets the lid rise only a few times higher, so that it fits.
  • The heater and the cooler move energy at a steady rate, and none is lost to the room, so the sloping parts of the graph are straight. The high setting moves energy twice as fast as the medium, and the medium twice as fast as the low. A real tube cooling in air cools quickly at first, then more slowly.
  • The particles are drawn speeding up far more than real ones: a real water particle at the model's hottest moves on average only about a quarter faster than one at its coldest. The drawing's speed follows the temperature and nothing else, so it holds steady through both flat parts of the graph, as the real speed does.
  • The run is sped up, and each part of it plays for at least a few seconds, so that the short parts can be seen. The time on the graph is the real time.
  • In the drawing, ice melts and water freezes from the bottom, next to the plate, and water boils from its surface. In real boiling water, bubbles of steam also form inside the water.
  • The time slider stops where the run ends: all steam at the model's hottest, or all ice at its coldest. At the low setting the run stops at the end of the slider, before all the water has boiled.

Numbers and their sources

Review

Demonstration: a simplified model. Checked against its written sources, 26 September 2026. Not reviewed by a qualified teacher.

Curriculum references

SC4-SOL-01SC4-WS-06ST3-6MW-SST3-DAT-01AC9S5U04AC9S5I04AC9S7U05AC9S7I05

Reference, not a verified alignment.

All demonstrations Practicals in the Lab