Recently in class, we performed a mini lab experiment with powders and vinegar. The goal was to have a balanced chemical reaction, meaning a certain amount of solid was supposed to produce a certain amount of gas. The mass relationship between the solid and the gas is mole to mole. It is a molar relationship because for every mole of solid used, a mole of gas was produced. This molar relationship means that the mass relationship applies to any and all chemical reactions. In every situation, a mole of any given type of solid will produce a mole of some sort of gas. While this is true, the mass of each mole will differ, so the mass ratio will be the same (1:1 mole:mole), but the amount of gas produced as a result of solid used will change from experiment to experiment.
In situations where an equations must be balanced, a molar relationship of 2:2 arises, but this situation still has the same principle as above.