Question

The moles of methane required to produce 81 g of water after complete combustion is _____ × 10^–2 mol. [nearest integer]

Answer 1

Correct Answer: 225

To solve this problem, we need to determine the amount of methane (CH₄) required to produce 81 g of water (H₂O) through complete combustion.

The balanced chemical equation for the complete combustion of methane is:
CH₄ + 2O₂ → CO₂ + 2H₂O

From the equation, we see that 1 mole of CH₄ produces 2 moles of H₂O.

First, calculate the moles of water produced. The molar mass of H₂O is approximately 18 g/mol.
Moles of H₂O = 81 g / 18 g/mol = 4.5 mol

According to the stoichiometry of the reaction, 2 moles of H₂O are produced from 1 mole of CH₄. Thus, the moles of CH₄ needed are:
4.5 mol H₂O × (1 mol CH₄ / 2 mol H₂O) = 2.25 mol CH₄

The result, 2.25 mol, can be expressed as 225 × 10^–2 mol when multiplied by 10².

Verification within the range: The computed value is clearly falling within the range provided, as it corresponds to 225 in a format of × 10^–2 mol.

Therefore, the answer is 225 × 10^–2 mol.