Stoichiometry

As we mentioned earlier, stoichiometry is simply a chemical recipe. We can work out how much reactant (ingredient) is required to form a certain amount of product. Stoichiometry relies on one major factor, a balanced chemical equation. From this balanced equation we derive the chemical ratio. The chemical ratio tells us the amount of product that is formed per amount of reactant used.

It sounds very complex, but its not, so lets go to an example just to simplify matters.

Hydrogen and oxygen react to form water according to the equation below
The equation tells us that for every 2 hydrogen molecules we require 1 oxygen molecule to produce 2 water molecules.
Question.How many mole of water are produced if 10 mole of hydrogen gas react completely.

Step 1 We identify the starting point in the equation.

This is always the point that we can calculate an amount of substance. In this case we know we have 10 moles of hydrogen gas.

 Stoichiometry depends heavily on a blanced equation and the ratios that are derived from the coefficients. The start coefficient The finish coefficient

Step 2 Identify the finish.
This is always the subject we need to find out. In this case it is the amount of water in mole

Step 3 Using the coefficients in the balanced equation derive the ratio, which is always finish divided by start.
2/2 = 1 the ratio is 1:1

Step 4 Multiply the ratio by the number of moles given at the start.

ratio X start = moles of water produced.

1 X 10 moles of hydrogen = 10 moles of water

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