Chemistry problem

Question

What is the greatest amount of magnesium oxide in moles that can be made with 6.3 mol Mg and 6.9 mol ? Which reactant is O2 limiting ? How many moles of the excess reactant will be left after the reaction ? 2 Mg+O2 --->2 MgO

Answer 1

Hello, Emily,

I'll assume you meant to type 6.9 moles of O₂. My answer is based on that assumption.

The balanced equation tells us the we need 1/2 mole of O₂ for every 1 mole of Mg, a molar ratio of 1/2. Thus, 6.3 moles of Mg would only require half that of oxygen, or 3.15 moles. We have 6.9 moles of O_2, so it is in excess. Mg is the limiting reagent. We can answer the first question already There will be (6.9 - 3.15) = 3.75 moles of oxygen left over.

Assuming all of the Mg reacts, we can see from the equation that we get 2 MgO for every 2 Mg, a molar ratio of 1:1. If all of the Mg reacts, we'll obtain 6.3 moles of MgO.

Bob