[John Bushnell]

How much energy is released when Hydrogen is combusted with Oxygen to produce one (US) gallon of water, and how many moles of Hydrogen are in one (US) Gallon of water?

I found on the internet, 286,000 jolues/mole of Hydrogen.

I found on the internet, 210 Moles of Hydrogen in a gallon of water.

Does this mean;
(286,000 jolues/) * (210 moles) => 60,060,000 joules of energy and one gallon of water? (@ 100% conversion efficiency)

When it says a mole of H does it actually mean a mole of H2?

I took a couple of undergraduate chemistry classes about 50 years ago, would like to get confirmation about the above questions.

Thank you,
John Bushnell 
Title:  Back Yard tinkerer

[mjc123]

That looks correct. 286 kilojoules of energy are released when 1 mole of H₂ is combusted to make 1 mole of water.

[Enthalpy]

Always check whether "combustion" produces gaseous or liquid water. -286kJ/mol is for the liquid.