Question

if you burn 51.4g of hydrogen and produce 459 g of water, how much oxygen reacted

Answer 1

Hydrogen is combusts to form water \[\text H_2+\text O_2\rightarrow\text {H}_2\text O\]
balancing the equation\[2\text H_2+\text O_2\rightarrow2\text {H}_2\text O\]
this says that 2 moles of hydrogen gas + one mole of oxgen gas → 2 moles of water

Answer 2

conservation of mass must be maintained, so if you start with 51.4g of hydrogen and finish with 459g of water, ALL the hydrogen must still be there, plus the remainder must be oxygen.

Answer 3

you need to know the molecule mass of the species involved to convert grams to moles

Answer 4

hmm @JFraser that is way simpler