How many moles of KClO3 are needed to form 2.8 L of O2, measured at STP, according to the following reaction: 2KClO3 ® 2KCl + 3O2

Answer 1

1 mol = 22.4 Liters at STP
so 2.8 L/(22.4 L/mol ) = 1/8 mol of O2 is formed
You need 2Mol of K... for 3 mol of O2
so 2/3 * 1/8 = 1/12 mol of KClO3 needed in perfect world

Answer 2

9? How did you get 9 ?????