# Why does lithium move on the surface of water during the reaction?

If someone asks me to number the most notable "textbook experiments" I would definitely name "the comparison of the reactions of alkali metals with water" among the most favorites.

We just happened to do such a reaction with small pieces (approximately $\text{7.5 g}$) of Li, Na and K. As we were supposed to write down anything that we observe, I came across an interesting phenomenon.

It seems that the answer is so simple, I didn't get it through many resources.

Li piece is moving rapidly (better call it spinning) on the surface of water as it is reacting with it and a subtle explosion sound is heard.

Why does the motion of Li on the surface of the water in the beaker take place? Could the heat released by the reaction be causing current in the water (I don't believe so, as the possibly hot water isn't involved in any convection currents)? Info you might need:

Our chemistry teacher cut a non-oxidized piece of well-preserved lithium. The piece of the reactant wasn't of any distinguishable geometrical shape. After repeating the experiment for several times, I sensed a headache that as I believe is because of release of the impurities of the sample.

• Hydrogen evolves, but why does it evolve in such an uneven fashion as to cause motion, and not just jiggling back and forth.. May 7 '16 at 3:59
• Could there also be some steam being generated from the heat of the reaction (at the lithium surface)? Same effect as the $\ce{H2}$ gas. Aug 14 '17 at 21:25
• I believe surface tension of water might play a role, too. Aug 14 '17 at 21:34
• 7.5 grams seems a lot! Aug 15 '17 at 5:15

$$\ce{2Li(s) + 2H2O(l) -> 2LiOH(aq) + H2(g)}$$