Calculating Energy Released by Sodium Reacting with Water

[xpell]

Hi! After watching a couple videos about the explosive reaction of sodium in freshwater and seawater, I felt curious and wanted to calculate how much energy is released. However, my Chemistry is super rusty and I think that my result is way too high (equivalent to almost 2 g of TNT per gram of sodium!) Would you please confirm or tell me where did I mess it up:?

The balanced equation for the reaction is:
2Na + 2H2O → 2NaOH + H2
Change in enthalpy for the reaction at 20ºC (ΔH20C) is: -368.6 kJ.
So, the energy released in the reaction = 368.6 kJ
Mass of 2Na (2 moles of sodium) = 23 x 2 = 46 grams
Energy released for 46 grams of sodium = 368.6 kJ
Hence, energy released for 1 g of sodium = 368.6/46 = 8,013 J ≈ 8 kJ (!)

PS. If someone is so kind to tell me how to calculate this under different conditions of water pressure / temperature, I'd appreciate it a lot too.

 

[Borek]

The explosion doesn't come from the sodium reacting with water, but from the hydrogen reacting with the oxygen, so the total output is even higher (but involves process that you haven't listed).

I see nothing wrong with your calculation (I am assuming you got the ΔH from some reasonably reliable source). There are plenty of materials that have higher energy density than TNT, so there is nothing surprising here.

 

[xpell]

The explosion doesn't come from the sodium reacting with water, but from the hydrogen reacting with the oxygen, so the total output is even higher (but involves process that you haven't listed).

Hey, thank you, I didn't know this! Would you please tell me more or point me to further reading about it?

 

[Borek]

Just google hydrogen explosion. Produced hydrogen mixes with the air, reaction produces enough heat to ignite the mixture. Kaboom.