Question by elliotwalker@ymail.com: witch fuel is lighter liquid hydrogen or gas hydrogen?
and i you factor in energy per volume witch one is better?

Best answer:

Answer by Larry
The first part is a trick question. Mass is not a property of a substance; it’s a property of a specific sample of that substance. Example: A 2-kg brick has more mass than a 1-kg brick; so the 1-kg brick is lighter.

Density is a different story. A liter of H2 liquid has greater mass–and greater density–than a liter of H2 gas. (At ordinary atmospheric pressure, the H2 would have to be extremely cold to be able to remain in the liquid state.)

The chemical energy of a given volume of H2 fuel is roughly proportional to the mass. So if I was cooking for a large group of people, I’d rather use a liter of H2 liquid than a liter of H2 gas. The H2 liquid has a greater energy per volume.

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