Question

how many moles of oxygen gas are needed to react with 4 moles c2h6?

Answer 1

First you have to know the reactants and balance that equation.
\[2C _{2}H _{6}+7O _{2} \rightarrow 4CO _{2}+6H _{2}O\]
So the mole to mole formula is simple.
\[Known Mole * \frac{ Unknown Mole Coefficient }{ Known Mole Coefficient }=Unknown Mole\]
Ratio of unknown to known is \[\frac{ 7 }{ 2 }\]
Just plug everything in and solve it:
\[4 * \frac{ 7 }{ 2 } = Moles of O_{2}\]
\[14 = Moles of O_{2}\]