# Sports, Physiology, and Health: Hydrogen Powered Bicycles "Run on Water"

Electric vehicles of all kinds are attracting increased interest everywhere, but electric bicycles are very popular in China (where there are over 120 million of them), the Netherlands, and India. They typically have a rechargeable battery pack and electric hub motor.

Electric hub motors on front or back wheels

A new electricity source combines a hydrogen fuel cell with a "sodium silicide" fuel cartridge, winner of a "Green Chemistry Challenge Award"[1]. The sodium silicyde reacts with water to make the hydrogen fuel [2][3][4]:

2 NaSi(s) + 5H2O(l) → Na2Si2O5(s) + 5H2(g) (1)

The composition of sodium silicide may depend on the method of synthesis. Silicides can be made by the reaction of active metals (like Mg) with sand, or by heating sodium with silicon. Dye et al [5] prepare sodium silicide by the reaction of sodium metal with silica gel, obtaining black powders of (hypothetically) Na4Si4 nanoparticles.

Equation (1) not only tells how many molecules of each kind are involved in a reaction, it also indicates the amount of each substance that is involved. Equation (1) says that 2 NaSi formula units can react with 5 H2O molecules to give 1 Na2Si2O5(s) formula unit and 5 H2 molecules. Here we're using the term "formula unit" to indicate that the substance may not be a molecule, but rather an ionic compound or ["network crystal"]. A "formula unit" gives the composition of the substance without specifying the type of bonding.

Equation (1) also says that 1 mol NaSi would react with 5 mol H2O yielding 1 mol Na2Si2O5(s) and 5 mol H2.

The balanced equation does more than this, though. It also tells us that 2 × 2 mol = 4 mol NaSi will react with 2 × 5 mol = 10 mol H2O, and that ½ × 2 mol = 1 mol NaSi requires only ½ × 5 = 2.5 mol H2O. In other words, the equation indicates that exactly 5 mol H2O must react for every 2 mol NaSi consumed. For the purpose of calculating how much H2O is required to react with a certain amount of NaSi therefore, the significant information contained in Eq. (1) is the ratio

We shall call such a ratio derived from a balanced chemical equation a stoichiometric ratio and give it the symbol S. Thus, for Eq. (1),

The word stoichiometric comes from the Greek words stoicheion, “element,“ and metron, “measure.“ Hence the stoichiometric ratio measures one element (or compound) against another.