Answer:
The correct answer is 35 L
Step-by-step explanation:
The complete combustion of methane (CH₄) gives carbon dioxide (CO₂) and water (H₂O) according to the following chemical equation:
CH₄(g) + 2 O₂(g) → CO₂(g) + 2 H₂O(g)
The water obtained in gas phase (H₂O(g)) is the steam.
As we can see, 1 mol of CH₄ reacts with 2 moles of O₂ to give 1 mol of CO₂ and 2 moles of H₂O.
We have 12.5 g of CH₄, so we have to first convert the mass to moles of methane by using the molecular weight (Mw) of CH₄
Mw CH₄= 12 g/mol + (4 x 1 g/mol)= 16 g/mol
moles of CH₄ = mass/Mw= 12.5 g/16 g/mol = 0.78125 moles
According to the chemical equation, the combustion of 1 mol of CH₄ produces 2 moles of H₂O. The water produced is the steam, so we have to multiply by 2 the number of moles we have to obtain the moles of H₂O-steam- we obtain:
0.78125 moles CH₄ x 2 moles H₂O/ mol CH₄ = 1.5625 moles H₂O
Finally, we know that 1 mol of gas at STP occupies 22.4 L, so we can determine the liters of steam that are produced as follows:
1.5625 moles H₂O x 22.4 L/ 1 mol H₂O = 35 L