Consider the following chemical reaction:

Question

2 KNO3 (s) ------------> 2 KNO2 (s) + O2 (g)
What volume, in liters, of O2 at 31.2oC and 2.045 atm pressure can be produced from the decomposition of 54.92 g of KNO3 (FM = 101.1 g/mol).

Answer 1

Always start with a balanced equation. You have that.
Convert 54.92 g KNO3 to mols. mol = grams/molar mass = ?
Using the coefficients in the balanced equation, convert mols KNO3 (what you have) to mols of what you want (mols O2). Then convert that to volume using PV = nRT. That gives you V at the conditions listed. Remember T is in kelvin.