Sublimation sim

What the sim shows

Iodine sublimes and sodium chloride does not. Iodine's vapour pressure (approximate standard data, joined by Clausius-Clapeyron lines): 0.0407 kPa at 25 °C, 12.07 kPa at its melting point, 113.7 °C, and one atmosphere when the liquid boils at 184.3 °C. Below 113.7 °C the solid turns straight into vapour, so gentle heat is the method; heated strongly it melts first. The vapour reaches the cool funnel and deposits on it, and the colour of the gas deepens with how much iodine is in it (about 600 dm³/(mol cm) near 520 nm, approximate). Ammonium chloride does not really sublime: NH₄Cl → NH₃ + HCl (ΔH = +176.2 kJ/mol, from enthalpies of formation), two colourless gases, which reach one atmosphere only at about 338 °C and join up again on the cool funnel. Desk estimates, not measurements: the burner gives the dish 21 W (gentle) or 92 W (strong) and it loses 0.3 W/°C, so it settles near 95 °C or 332 °C; vapour moves to and from surfaces at 5 mm/s; warm gas rises out of the stem like a chimney and the cotton wool passes 8% of that flow. Not counted: the heat the solid takes to change state, gas escaping under the funnel's rim, the room the mixture takes in the dish. The clock runs 40 times faster than real time.

• Grey-black: iodine crystals
• Purple: iodine vapour
• White: sodium chloride, ammonium chloride, cotton wool

Use it in your lessons

• Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
• Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
• Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.

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