Step 1
The reaction provided:
2 Mg (s) + O2 (g) => 2 MgO (s) (completed and balanced)
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Step 2
Information provided:
40.0 g of O2 which react completely
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Information needed:
The molar masses of:
O2) 32.0 g/mol
MgO) 40.3 g/mol
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Step 3
By stoichiometry,
2 Mg (s) + O2 (g) => 2 MgO (s)
32.0 g O2 ------- 2 x 40.3 g MgO
40.0 g O2 ------- X
X = 40.0 g O2 x 2 x 40.3 g MgO/32.0 g O2
X = 101 g MgO
Answer: C 101 g
