• Question: How much Francium (Fr) is needed to make the Earth explode?

    Asked by anon-267549 on 10 Nov 2020.
    • Photo: Sam Geen

      Sam Geen answered on 10 Nov 2020:

      I enjoy this question a lot. It’s been a while since I did chemistry, so others feel free to correct me if I’m wrong.

      Francium reactions are a bit difficult because it’s very unstable and nobody has made much of it. Some people have estimated that it would make about 1000 kJ per mole if it reacted with water, which is about 4.4 MJ per kg.

      The Earth’s binding energy (how much energy it would take to reverse its gravity) is about 4 times 10^32 J, or 4 with 32 zeros after it Joules. If my calculations are correct, you would need a lot more francium than the mass of the Earth to blow it up completely. You would also need to put it in the middle of the Earth to stop the energy escaping into space, and do it quickly because it decays radioactively on average after around 22 minutes.

      You might actually get more energy from francium from this radioactive decay – it produces energetic radioactive beta emission, which can be absorbed easily by the Earth. A lump of francium 10,000 times less massive than the Earth might be enough to blow it up.

      * https://www.osti.gov/biblio/136340-standard-enthalpies-formation-francium-hydroxide-hydrates

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