Combustion problem in chem?

the combustion of propane ( C3H8) produces CO2 and H2O:

C3H8 + 5O2 --> 3CO2 + 4H2O

The reaction of 2.5 mol of O2 will produce how many moles of H2O

if you could please explain how you got the answer that would help, since this is an example problem for a test.

Pretty easy answer. 5 mols of O2 will make 4 mols of H2O. If the amount of O2 is cut in half, so will the amount of H2O is can produce. So the answer is 2 mols of H20.
this is a simple stoichiometry problem

you have 2.5 moles of oxygen, and you need to find out how many moles of water you can create out of 2.5 moles of oxygen.

to do this you use the conversion factor between the elements located in the chemical equation. You see that for every 5 moles of O2, 4 moles of H2O are created, therefore the conversion factor is 4molwater/5molO2

so you have 2.5 moles O2 * (4molH2O / 5molO2) = 2 moles H2O. Notice how the units of oxygen cancel as well from the numerator and the denominator, leaving only moles of water. That is your answer. 2 moles of water for evey 2.5 moles oxygen.

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