If 3 moles of calcium are reacted with 3 moles of oxygen, then how many moles of CaO are formed?

The balanced chemical equation for the reaction between calcium and oxygen to form calcium oxide (CaO) is:

2Ca + O2 → 2CaO

From this equation, we can see that 2 moles of calcium react with 1 mole of oxygen to produce 2 moles of calcium oxide.

If we have 3 moles of calcium and 3 moles of oxygen, the calcium is in excess because we only need 1.5 moles of oxygen to react with 3 moles of calcium (according to the stoichiometry of the balanced equation).

Therefore, all 3 moles of oxygen will react, and they will react with 23 = 6 moles of calcium to produce 23 = 6 moles of calcium oxide.

So, 6 moles of CaO are formed.