How much energy does 5 grams of hydrogen produce?
Hydrogen gas will burn in oxygen to produce water. This is a very clean combustion process and the reason why many people are pushing the concept of using hydrogen as an energy-producing fuel. When 5 grams of hydrogen burns in oxygen it produces about 700 thousand joules of energy.
To put that number into context, it's good to see a couple of examples that show how big a joule of energy is. If you hold a 20-pound chair at arms length and drop it, when it hits the ground it has about 100 joules of kinetic energy. A baseball traveling at 100 miles per hour has about 150 joules of kinetic energy. The WBZ radio station is rated at 50 kilowatts which means it radiates 50,000 joules of electromagnetic energy every second.
Our sun uses hydrogen to produce energy in a slightly different manner: nuclear fusion. The process is actually quite complex and uses several intermediate steps, but the basic idea is that 4 hydrogen atoms fuse together to make 1 helium atom and a prodigious amount of energy. If we start with 5 grams of hydrogen, we end up with about 4.97 grams of helium plus 3.2 trillion joules of energy! The ultimate amount of energy that 5 grams of hydrogen can provide is yielded when we annihilate the 5 grams of hydrogen with an equal amount of anti-hydrogen. In this case the total amount of energy produced is 900 trillion joules. Of course, using current techniques to make 5 grams of antihydrogen (one atom at a time) would use up far more energy than that and cost quite a lot of money.
Dr. Knowledge is written by physicists Stephen Reucroft and John Swain, both of Northeastern University. E-mail questions to drknowledge@globe.com or write Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.
