Answer:
About 16.1 grams of oxygen gas.
Explanation:
The reaction between magnesium and oxygen can be described by the equation:

24.4 grams of Mg reacted with O₂ to produce 40.5 grams of MgO. We want to determine the mass of O₂ in the chemical change.
Compute using stoichiometry. From the equation, we know that two moles of MgO is produced from every one mole of O₂. Therefore, we can:
- Convert grams of MgO to moles of MgO.
- Moles of MgO to moles of O₂
- And moles of O₂ to grams of O₂.
The molecular weights of MgO and O₂ are 40.31 g/mol and 32.00 g/mol, respectively.
Dimensional analysis:

In conclusion, about 16.1 grams of oxygen gas was reacted.
You will obtain the same result if you compute with the 24.4 grams of Mg instead:

That kilo-pascal is equivalent to 1678. 64 millimeters of mercury pressure
Answer:
0.670 mol
Explanation:
Step 1: Write the balanced reaction for the decomposition of alumina
2 Al₂O₃ ⇒ 4 Al + 3 O₂
Step 2: Calculate the moles corresponding to 34.2 g of Al₂O₃
The molar mass of Al₂O₃ is 101.96 g/mol.
34.2 g × 1 mol/101.96 g = 0.335 mol
Step 3: Calculate the moles of Al produced from 0.335 moles of Al₂O₃
The molar ratio of Al₂O₃ to Al is 2:4.
0.335 mol Al₂O₃ × (4 mol Al/2 mol Al₂O₃) = 0.670 mol Al