I spend a lot of time thinking about geeky things. This probably isn’t surprising. Also unsurprisingly, a lot of this geekly energy is directed toward inflation.

For example: Water can be broken down into hydrogen and oxygen. There have been a few inflation stories that have made use of this device. But have you ever wondered how much expansion results from turning water into hydrogen and oxygen gas?

You probably haven’t, but I have. Yes, this is the sort of silliness I sometimes ponder when working out story plots. Gird thy loins, there’s math afoot.

The short answer: A whole crapload of expansion

The long answer:

Water has a molar mass of 18.0153 g/mol. Since 1 liter of water conveniently weighs 1kg, we can calculate:

18.0153 g/mol * 1 liter/1000 g = 55.5084 mol/liter

And now for the conversion from water to gasses. Oxygen and hydrogen gas are O2 and H2, respectively, so the conversion is:

1 mol H2O = 1 mol H2 + 0.5 mol O2 or 2 mol H2O = 2 mol H2 + 1 mol O2 if you prefer round numbers

Either way, you’re getting one and a half moles of gas for every mol of water.

So 1 liter of water will turn into 83.2627 moles of gas. Truth be told, I always hated working with moles as a unit of measurement in chemistry, but it’s actually kinda convenient for dealing with gasses. One mole of gas takes up the same amount of space at a given temperature and pressure, regardless of the gas. The Ideal Gas Law tells us that 1 mole of gas will take up 24 liters of volume at room temperature.

83.2627 mol * 24 liters/mol = 1998.3037 liters

So when you convert water to hydrogen and oxygen, it increases to roughly 2000 times its original volume.

If some hapless victim were to drink a liter of water which (through some plot device to be determined) spontaneously broke down into its component elements, she’d blow up into a sphere just over five feet in diameter.

The resulting mixture of gas is lighter than air, but you’ll need a lot more than one liter of water to get a person airborne. We can save that math for another time.

Average: 4.5 (2 votes)
AlecDeluxe's picture

Looks like someone's been reading BOOKS...!!

I want to pop so much I could burst!

LutherVKane's picture
Yeah, paid way too much

Yeah, paid way too much attention in my science classes. They say a little knowledge is a dangerous thing...

I enjoy this sort of exercise. The main value to understanding the science behind the various inflation devices is knowing which laws of physics (or chemistry, or whatever) I'm breaking when I write a story.

There are a few more scenarios to explore, and they'll eventually wind up here. But they're rambling and I doubt many people who aren't me actually care about such things, so I'll avoid inflicting them upon the general forum.

bellyexpansion (not verified)
I totally agree with you, I

I totally agree with you, I love this kind of explanations too :D

Do you have more of them?

LutherVKane's picture
A few in various states of

A few in various states of completion. Is there any subject in particular that you'd like me to tackle?

bellyexpansion (not verified)
Well, before that I would

Well, before that I would really like to see those one first ;)

But anyway, I was thinking of something that has to do with the "simple" law which explains you that if you heat up a fluid (both liquid or gas), it expands, or something like that (i.e. find out how many liters of water/air/whatever should a person ingest, which temperature should the water/air/etc. reach, the final volume...stuff like that ;)

LutherVKane's picture
Thermal expansion was one of

Thermal expansion was one of the topics I considered covering. A few others:

  • Relationships between volume and pressure.
  • Relationship between pressure and energy (or, why breast implants don't explode).
  • Buoyancy, why/how things/people float in air/water, how much helium it takes to get a person airborne and the like.

Thermal expansion is pretty straightforward and should be simple to tackle.

bellyexpansion (not verified)
Go for it! ;)

Go for it! ;)

LutherVKane's picture
Granted. You have two wishes


You have two wishes remaining :)

bellyexpansion (not verified)
Hehe ;-p Anyway, you think

Hehe ;-p

Anyway, you think you'll post the other ones soon?

LutherVKane's picture
The post on helium is almost

The post on helium is almost done. It'll be going up soon.