So these numbers, these coefficients, in this case, one, one, one, in this case, one seven over two, two and three will never represent mass. So never kilograms, never grams, never pounds, never any type of mass. Only moles atoms or molecules. In other words, 1 mol of this hydrocarbon reacts with seven over two moles of diatomic oxygen to produce two moles of carbon dioxide and three moles of water. We can never say 1 gram of this car react with seven over 2 grams. That makes no sense.