Answer:
Mass of HCN produced = 6.75 g
Explanation:
Reaction is as follows:

First calculate the no. of moles of each chemical species.
molecular mass of
is 17 g/mol
No. of mol of
= 11.5/17 = 0.676 mol
Molecular mass of
= 32 g/mol
No. of mol of
= 12/32 = 0.375
Molecular mass of
= 16 g/mol
No. of mol of
= 10.5/16 = 0.656 mol
from the balanced chemical reaction, it is clear that 2-moles ammonia reacts with 3 moles oxygen and 2 moles methane to form 2 moles of HCN.
or, 1-mol ammonia reacts with 1.5 mol oxygen and 1 mol methane to form 1 mol of HCN.
Thus, no. of oxygen present is less than required and so it will act as limiting reagent.
From the chemical equation,
3 moles oxygen produces 2 moles HCN
or one mole oxygen produces (2/3) moles HCN
0.375 moles oxygen produces (2/3) × 0.375 HCN = 0.25 moles of HCN
molar mass of HCN = 27 g/mole
Mass = mol × molar mass
mass of HCN = 27 × 0.25 = 6.75 g