What the Phase Change Gizmo Actually Does
The Phase Change Gizmo is an ExploreLearning simulation that lets you drag a thermometer into a beaker of water and heat or cool it to watch states shift. It tracks temperature over time and plots a heating curve. That's basically it. It's meant for middle school and early high school science classes. Teachers assign it. Students run through it. Some need the answers to check their work or finish up before the bell. There isn't one official PDF that ExploreLearning publishes. The gizmo generates data as you interact with it, so the "answers" are really just the observed results from running the simulation correctly. That said, several education sites host compiled answer sheets that list the expected temperatures and observations. The most reliable ones mirror the actual simulation values, which means they tend to be updated when ExploreLearning patches the gizmo. I've used a few different keys over the years. The ones that match closest are the ones that show the plateaus at 0°C for freezing and 100°C for boiling at standard pressure. Anything that claims phase changes happen at different temperatures without noting pressure adjustments is usually wrong or pulled from an outdated version.
How to Run the Gizmo and Get the Right Readings
Open the gizmo, set the initial temperature of the water, then either add heat or remove it. The default setup usually starts at around minus 50°C for ice. Turn the heat source on and watch the graph. The temperature rises, plateaus during the melt, rises again during the liquid phase, plateaus at the boil point, then rises once more as steam. Record these values in the table the gizmo provides: Starting temperature of ice: approximately minus 50°C depending on your settings
Melting point plateau: 0°C at standard atmospheric pressure
Boiling point plateau: 100°C at standard atmospheric pressure
Final temperature of steam: whatever the gizmo reaches when you stop heating
The key thing students miss is that the temperature stays flat during a phase change even though heat is still being added. That's latent heat, and the gizmo shows it clearly. If your answer key says the temperature keeps climbing during melting or boiling, something is off.
Get the Full Details
A Real Problem I Ran Into
A few years ago, a student brought me a printout where the melting plateau was showing at about 2°C instead of 0°C. The gizmo hadn't been adjusted, the water was supposedly pure, and everything looked normal. I dug into it and found the issue was that the simulation had accumulated floating point rounding errors across multiple runs in the same browser session. Closing the tab and reloading the gizmo fresh fixed it immediately. The plateau snapped back to exactly 0°C. This is worth knowing because some answer keys online list slightly off values, and students assume the gizmo is broken when really it's just a quirk of the software. A hard refresh usually resolves it.
Things the Gizmo Doesn't Tell You Clearly
The simulation assumes standard atmospheric pressure the whole time. If you change the pressure setting, the phase change temperatures shift. The gizmo does let you adjust pressure, but it doesn't emphasize that enough. At lower pressures, water boils below 100°C. At higher pressures, it boils above 100°C. The answer key you use should reflect the pressure setting you're running with, or it won't match your data. Another thing that trips people up is the difference between the heating curve graph and the state of matter labels. The gizmo shows solid, liquid, and gas labels, but it also shows sublimation and deposition paths if you run it in certain modes. Not all answer keys account for those alternate pathways, so if your teacher assigned the sublimation variation, a standard key won't cover it.
How Long This Usually Takes
Running the full phase change gizmo from ice to steam and filling in the table takes most students about 8 to 12 minutes. If you already know what values to expect and just need to confirm them, you can knock it out in roughly 4 minutes. The answer key part, assuming you have one open while you work, takes maybe another 2 minutes to verify your numbers. Some teachers ask follow-up questions that go beyond the raw data, like why the melting plateau is shorter than the boiling plateau or what happens to the molecular motion during each phase. The gizmo shows the particles moving, but it doesn't explain the energy distribution behind it. If your assignment includes those kinds of questions, an answer key alone won't help you. You need to understand that during a phase change, the added energy goes into breaking intermolecular bonds rather than raising temperature. That's the core concept, and it's what most teachers actually grade on. I've seen students copy the temperature values perfectly and still lose points because they couldn't explain the plateau. Make sure you can actually say why the temperature stays flat, not just where it stays flat.
