Chilling effects – a spontaneous endothermic demonstration

It’s easy to find plenty of dramatic demonstrations of exothermic reactions, but most endothermic reactions don’t leave much of an impression.

However, a dramatic impression might be needed to shake the misconception some students hold that endothermic reactions cannot occur spontaneously. This is where the solid–solid reactions of barium hydroxide with ammonium salts are useful. Here we demonstrate two.

Read the article that accompanies this video in the November 2016 issue of Education in Chemistry at

This is part of the Education in Chemistry Exhibition Chemistry series: chemistry demonstrations to capture your students’ imaginations:

0:14 Cup of coffee with beans by Petr Kratochvil [Public domain], via Wikimedia Commons
0:14 Et baal.jpg by Einar Helland Berger (Own work) [CC BY-SA 2.5 (], via Wikimedia Commons


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  1. I don't understand this at all. The whole thing seems to be counter intuitive. The temperature plummets and the solid turns to liquid, it is giving off heat but it freezes the water below it. I know heat rises but it is clearly taking heat away from the water and the wooden block. Is the heat only being given out through the vapours. I'm a little rusty with my chemistry so can someone break this down for me?

  2. I have some student to want to do some quantitative experiments with this reaction, but we don't have any ammoniumthiocyanate available. Would for instance ammoniumnitrate or chloride work just as well?

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