The reaction of the decomposition of water into oxygen gas and hydrogen is balanced as such:
[tex]2H_{2} O -> 2H_{2} + O_{2}[/tex]
Using conversion factors, 2.0 mol H2O is equivalent to 1 mol O2, as per the reaction.
1 mol O2 is equivalent to 32g O2 (1 mol O2 * [tex]\frac{32 g O2}{1molO2}[/tex] )
Answer: 32 g of oxygen.
