Oxygen gas can be generated by heating KClO3 in the presence of some MnO2.

Question

2KClO3 → 2KCl + 3O2
If all the KClO3 in a mixture containing 1.00 g KClO3 and 0.25 g MnO2 is decomposed, how many liters of O2 gas will be generated at T = 24.0°C and P = 755.6 torr?

Answer 1

Convert 1.0 g KClO3 to mols. mols = grams/molar mass. (I am assuming the MnO2 is a catalyst and does not enter the reaction).
Using the coefficients in the balanced equation convert mols KClO3 to mols O2.
Then use PV = nRT and the conditions listed in the problem to solve for V. Remember to convert T to kelvin.