What are some real life uses of stoichiometry?
The principles of stoichiometry can be used while cooking.
If you were almost out of a specific ingredient, you could use the principles of stoichiometry to figure out how much of every other ingredient you would need (treating the ingredient you were almost out of as the "limiting reagent").
Stoichiometry continues to be useful in many walks of life—a farmer determining how much fertilizer to use, figuring out how fast you have to go to get somewhere in a specific period of time, or just to make conversions between systems like Celsius and Fahrenheit.
It is the life line of Chemistry. It is kind of history of Chemistry. It can be used to estimate the weights and constituents of an unknown substance.
Stoichiometry originally served the purpose of relative weight measurements, that evolved into the standard of AMU (Atomic Mass unit), where you compared ratio of a large variety of elements (not compound) with a standardized element - usually Carbon.
Hence, suppose if we break down 10 kg carbon dixodie into Carbon and Oxygen, then the 'volume' occupied will be 3.33 c.c. Carbon, and rest of volume oxygen. Of course going by precision, it is weights we measure. Then Carbon containing box has two times less mass than Oxygen containing box. Hence, the ratio of carbon to Oxygen is 1/2. AMU is 0.5. Comparing the same mass with other elements we get the same.
In practical life, battery cells, in corrosion of House painting, amount of water pollution etc. everything is measured in terms of relative weights a.k.a Atomic mass units.