In a chemistry lecture, the teacher has told that if two compounds react with each other and form two or compounds in two different ratios, then it is sure that both the reactants are used completely.
Example: $\ce{C + $\frac{1}{2}$ O_2 -> CO_2 + CO}$
My question here is, What is happening here? Are there two reactions that are taking place ( One with $\ce{C}$ and $\ce{O2}$ and other with $\ce{O2}$ and $\ce{CO}$ ) and is it always the case?
And does this happen with more than 2 reactants?
There are two possible parallel reactions:
\begin{align} \ce{2 C + O2 &-> 2 CO}\\ \ce{C + O2 &-> CO2} \end{align}
The latter reaction can run in a single step, or as a series $\ce{2 C + O2 -> 2 CO}$ and $\ce{2 CO + O2 -> 2 CO2}$.
$\ce{C}$ reacts with $\ce{O2}$ in molar ratio 2:1 or 1:1. If the initial ratio is between 2:1 and 1:1, there is possible that both reactant are spent, forming $\ce{CO + CO2}$ mixture. There is obviously also possibility the reaction does not complete and some of one or both reactants willremain.
But if the $\ce{C : O2}$ ratio is less than 1:1, than some $\ce{O2}$ will remain even if all $\ce{C}$ is spent. OTOH, if the $\ce{C : O2}$ ratio is more than 2:1, than some $\ce{C}$ will remain even if all $\ce{O2}$ is spent.
Many chemical tasks are trivial, if one does not seek for chemistry black magic everywhere. Compare it with this non-chemistry task:
Children get each 1 or 2 apples as a snack for a trip. If there are more than twice apples as children, some apples would remain, If there is less apples than children, some children will not get any apple.
