# What does “stoichiometric amounts” mean?

Can anyone inform me what the term stoichiometric amounts means? I know what stoichiometry means. It is the:

The relationship between the relative quantities of substance taking part in a reaction or forming a compound.

But what is "stoichiometric amount" supposed to be?

• Stoichiometric just means element measure. With regard to a balanced chemical reaction equation, the reactants are in stoichiometric proportion if the reactants are in ‘just right’ proportion: no reactant is limiting or present in excess. In a sense, it is ‘least wasteful’. But, as one of the answers notes, real world situations may make it necessary to have non-stoichiometric conditions, e.g., synthesizing cisplatin from an expensive platinum reactant plus an inexpensive reactant. See wiki for cisplatin. Then the cheap reactant may be used in excess to avoid wasting the expensive reactant. – Ed V Feb 29 at 14:40

Let’s take the simple example of the combustion of hydrogen $$\ce{H2}$$ in oxygen $$\ce{O2}$$. The equation of the reaction is: $$\ce{2 H2 + O2 -> 2 H2O}$$ It means that $$2$$ moles of $$\ce{H2}$$ $$(2\cdot2\ \mathrm g$$) react with $$1$$ mole ($$32\ \mathrm g$$) of $$\ce{O2}$$. These masses are in a ratio $$4:32=1:8$$. All mixtures containing $$\ce{H2}$$ and $$\ce{O2}$$ in a proportion $$1:8$$ are said to be “in stoichiometric amounts”.
If you use $$0.7\ \mathrm g$$ $$\ce{H2}$$ and $$5.6\ \mathrm g$$ $$\ce{O2}$$ to produce water, or if you have reacted $$1.10\ \mathrm g$$ $$\ce{H2}$$ and $$8.80\ \mathrm g$$ $$\ce{O2}$$, the components of the gas mixture are said to be “in stoichiometric amounts”.