Question

How many grams of O2 are needed in a reaction that produces 79.0g of Na2O?

Answer 1

First you need to know how many moles of the product are formed, and then compare the moles of product to moles of O2. Then convert moles of O2 to grams and you have your answer.

73.0g Na2O / 62 g / mol = 1.18 moles Na2O

There's 2 moles of Na2O formed per every moles of O2 based on the equation, so you require half as many moles of O2

1.18 / 2 = 0.59 moles O2 required

now multiply by the molar weight of O2

0.59 moles O2 * 32 g / mole = 18.88 g O2 required