Can you explain what stoichometry actually is and why the ratio is not the same as the number of moles?

Stoichiometry is just a way of relating two species that react, in a ratio. EXAMPLE: 1A + 2B -> 3C Now usually this would be written as A + 2B -> 3C but I've written the 1 to exaggerate the point. Now say you have 1 mole of A and 2 moles of B, in this case THE STOICHIOMETRY is equal to the moles. But if you have say 0.5 moles of A, you cannot say you have 1 mole of A can you. The stoichiometry is then only useful in determining how much of something you produce or react. So if you were told that the reaction goes to completion, you can work out how many moles of B and C you have, (Useful in equilibria). So the stoichiometry ratios are 1A:2B:3C So if you have 0.5 moles of A, you will react 2 x 0.5 = 1 mole of B and 3 x 0.5 = 1.5 moles of C will be produced.