Water Decomposition by Electrolysis

Dissociation of water molecules:

One aspect of water that is important in understanding electrolysis is its dissociation or ionization. In normal aqueous solution there is a certain probability that a hydrogen nucleus (a proton)can exchange between two hydrogen bonded molecules:

(The hydronium ion, H3O+, will be associated with additional water molecules through H-bonding.To simplify we will just write H+, with the understanding that it refers in fact to hydrated hydronium ions in aqueous solution. ) The reaction is not highly favored, so in neutral solution (no excess H+) there will only be 10X E-7 molar hydronium ions, in other words only about 2 of every billion water molecules will be protonated!

Electrolysis of Water

With the addition of electrical energy, water (H2O) can be dissociated into the diatomic moleculesof hydrogen (H2) and oxygen (O2).  The electrolysis of one mole of water produces a mole of hydrogen gasand a half-mole of oxygen gas. The process must provide enough energy for the dissociation and the energy to expand the produced gases.These reactions can be expressed as:

Interesting Facts

At Standard Temperature and Pressure (STP) or 20 degree Celsius and 1 atmosphere pressureone mole of gas occupies a volume of 22.4 liters. One liter is equal to 1.06 quarts, so one gallonis equal to 3.76liters. This make 22.4 liters equal to 5.9 gallons. At STP 5.9 gallons of hydrogen gas gas weighs 2 grams or0.0044 pounds. A gallon of water weighs 8.35 lbs, a gallon of gasoline weighs 6.5 pounds, and agallon of liquid hydrogen weighs about 0.63 pounds. It takes about 3.5 gallons of liquid hydrogen to equal the energy contentof one gallon of gasoline (gge), but that equates to 2.2 pounds of hydrogen to 6.5 pounds of gasoline.Under standard conditions it takes 0.065 kWh to dissociate one mole of water to produce one mole of hydrogen. To produce 2.2 pounds of hydrogen which is equivelant to one gallon of gasolinerequires 32.9 kW. It requires 29 pounds of water to produce 2.2 pounds of hydrogen. To put thisin perspective the average American house uses 24 kilowatts of electricity per day. The energy in 2.2 pounds of hydrogen would run theaverage American house for 1.5 days.

To learn how to run your car on hydrogen click here.