2 Responses

1. Fossil fuels and hydrogen pertain more to the first law than the second. The second states that entropy will increase in a closed system… but the earth is not a closed system, so it doesn’t really apply.

   The first law, on the other hand, states that energy can neither be created nor destroyed. Fossil fuels contain energy that was captured by plants (which were then eaten by animals, which were eaten by other animals, etc) millions of years ago. The energy store in hydrogen, likewise, has to come from somewhere. In most cases, it comes from electrolysis of water, which requires energy. Due to the inefficiency inherent in all systems, it takes more energy to crack the water into hydrogen and oxygen than you will get out of it by burning or fuel cells (the same way that we get less energy out of fossil fuels than was put into them by the sun). Unless we can harness solar power (or some other power source that’s equally abundant), then we’ll end up losing energy overall by switching to hydrogen fuel.

   Of course, this is just from a thermodynamics standpoint – there are plenty of other concerns, like waste products (i.e. CO2), byproducts of processing and refining, final costs, etc.

2. Most hydrogen is made from coal, natural gas, or petroleum.
   While it *can* be made by electrolysis in practice it is not.

   The production of hydrogen is not especially energy efficient; some 40% of the energy in the coal or petroleum is lost in the conversion.