• Question: If i was to create a chemical reaction involving mass amounts of potassium and and equal mass of water, What would happen? Would the reaction the the same just on a bigger scale or would it have a more devastating effect?

    Asked by jo3106 to Ben, Dave, Ed, Sam, Susana on 14 Jun 2013.
    • Photo: Benjamin Hall

      Benjamin Hall answered on 14 Jun 2013:

      I’d imagine the reaction would be the same just on a bigger scale.

      2 moles of Potassium react with 2 moles of water. Water has a lower atomic mass than potassium so to achieve equal masses you’d need more moles of water than of potassium to get an equal amount, so all of the potassium would react.

      Therefore what would probably happen is a massive amount of potassium would cause a massive amount of hydrogen gas to be released. The heat released by the reaction is enough to ignite the hydrogen, which is very explosive if there’s enough oxygen present! So there’d be a very big bang!

    • Photo: Sam Horrell

      Sam Horrell answered on 14 Jun 2013:

      As Ben has said below it would be scaled up and more dangerous. If i remember, throwing a bit of potassium into some water it fizzed around on the top of the water until it disappeared. Big block of potassium in a swimming pool you’re likely to get a bigger bang.

      If you’re really looking for something spectacular, a smaller amount of alkali metals lower down in the periodic table (Rubidium, cesium, francium) are much more reactive. I’m sure I’ve seen some youtube videos where francium is thrown into a bathtub. Lets just say the bathtub didn’t stand a chance.

    • Photo: David Briggs

      David Briggs answered on 15 Jun 2013:

      I think this is a really interesting question, Jo,

      As you probably know – Potassium reacts violently with water to produce Potassium Hydroxide and Hydrogen gas. The hydrogen gas can get ignited by the energy produced in the reaction and explode. I guess your chemistry teacher has already showed you this – but if not – it looks a bit like this:

      I would imagine that the more potassium you add, the more hydrogen that gets produced, the bigger the bang! The rate at which the hydrogen gas is produced is probably controlled by the surface area of the potassium – how fast the water can get to the potassium metal. If you used a large block of potassium it would react more slowly that if you used the same amount of powdered potassium. But it would be cool to try!

    • Photo: Susana Teixeira

      Susana Teixeira answered on 17 Jun 2013:

      Ah, Science lovers or not we all tend to remember this one from our school days!

      The others have already answered, but if you use equal masses there would not be enough potassium to react with all the water. If you used massive amounts of potassium to begin with, you would still produce a lot of hydrogen, which can ignite, and you would have significant amounts of heat released from the reaction itself. So in a way it would be the same on a bigger scale, but I would expect a very loud explosion (hydrogen is a big show off…)

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