Question

The chemical equation below shows the burning of magnesium (Mg) with oxygen (O2) to form magnesium oxide (MgO).

2Mg + O2 2MgO

The molar mass of O2 is 32.0 g/mol. What mass, in grams, of O2 is required to react completely with 4.00 mol of Mg?
A)2.00
B)64.0
C)128
D)256

Answer 1

convert to mol O2 using stoichiometry
4 mol mg * 1 o2 / 2 mg = 2 mol O2

convert mol O2 to grams using molar mass
2 mol O2 * 32 g/mol = 64 g O2

answer B

Answer 2

B) Mass of O2 required = 64.0 g

Step-by-step explanation:

Given:

Moles of Mg = 4.00 moles

To determine:

Mass of O2 that reacts completely with 4 moles of Mg

Step-by-step explanation:

The given reaction is:

2Mg + O2 → 2MgO

Based on the reaction stoichiometry:

2 moles of Mg reacts with 1 mole of O2

Therefore, 4 moles of Mg will need:

`= (4\ moles\ Mg * 1\ mole\ O2)/(2\ moles\ Mg) = 2\ moles \ O2\\`

Molar mass of O2 = 32 g/mol

`Mass\ of\ O2\ required = moles*molar\ mass \\\\= 2.00\ moles * 32\ g/mol = 64\ g`