Question

If you burn 49.4 g of hydrogen and produce 441 g of water, how much oxygen reacted?

Answer 1

The following combustion / oxidation reaction occurs when hydrogen is burnt ,

...................................................................2H2 + O2 = 2H2 O

stoichiometrically...............2 moles of H2 react with 1 mole of O2 to produce 2 moles of water

given no. of moles......H2 = 49.4 / 2 = 24.7 moles.are burnt ; H2 O = 441 /18 = 24.5 moles are produced

As per stoichiometric relation ,

the number of moles of O2 required for burning hydrogen is half the number of moles of hydrogen taken

and number of moles of water produced is equal to moles of hydrogen used

so when 24.7 moles of hydrogen is used then oxygen reacted = 12 .35 moles

Again 24.7 moles of water is produced when 12.35 moles of oxygen is reacted

24.5 moles of water would require oxygen = ( 12.35 x 24.5 ) / 24.7

........................................................................... = 12.25 moles

.......................................................................or ,= 12.25 x 32

......................................................................... = 392.00 gms.

===========================================================================================