Answer
No, the mass of H2O that will be produced by 9g oxygen = 10.14 g, NOT 18 g.
Explanation
Given:
2H2 + O2 → 2H2O
mass of oxygen = 9 g
Required: If the mass of H2O that will be produced by oxygen will be 18g
Solution:
Step 1: Find the number of moles of Oxygen
n = m/M where n is the moles, m is the mass and M is the molar mass
n = 9g/31.998g/mol
n = 0.281 mol
Step 2: Use the stoichiometry to find the moles of H2O
The molar ratio between H2O and O2 is 2:1
Therefore moles of H2O = 0.281 x 2 = 0.563 mol
Step 3: Calculate the mass of water from the moles
m = n x M
m = 0.563 x 18.02 g/mol
m = 10.14 g
