How many moles of hydrogen fluoride will react with #5.90# moles of silicon dioxide to produce silicon tetrafluoride?
The key to this problem is the balanced chemical equation for this reaction.
#color(red)(4)"HF"_text((g]) + "SiO"_text(2(s]) -> "SiF"_text(4(g]) + 2"H"_2"O"_text((l])#
Notice that you have a
This tells you that regardless of how many moles of silicon dioxide take part in the reaction, the reaction will always consume
In your case, you need to know how many moles of hydrogen fluoride will be needed to react completely with
To react completely simply means that all the moles of silicon dioxide must be consumed in the reaction.
So, use the aforementioned mole ratio to get
#5.90color(red)(cancel(color(black)("moles SiO"_2))) * (color(red)(4)" moles HF")/(1color(red)(cancel(color(black)("mole SiO"_2)))) = color(green)("23.6 moles HF")#