Stoichiometry

The difference between a recipe and a balanced equation is that a recipe tells you how much flour you need in terms of something you can measure.

 

 

Chemical equations relate numbers of atoms or moles.

2 moles of Na and 1 mole of Cl2 combine to form 2 mole of NaCl

 

So, for equations to be useful they have to be related to a quantity we can measure like grams.

Typically, the question is
"How many grams of Na are needed to completely consume 3.49 g of Cl2?"