In the partial cracking of methane, 7 mol of acetylene were formed. How much methane has decomposed?

In accordance with the condition of the problem, we write the following equation:
2CH4 = C2H2 + 3H2 – methane cracking occurs at a temperature of 500 degrees and is accompanied by the release of acetylene and hydrogen;
Calculations by formulas:
M (CH4) = 16 g / mol;
M (H2) = 2 g / mol.
According to the equation, we make up the proportion:
X mol (CH4) – 7 mol (C2H2);
-2 mol            – 1 mol from here, X mol (CH4) = 2 * 7/1 = 14 mol.
We find the mass of methane by the formula:
m (CH4) = Y * M = 14 * 16 = 224 g.
Answer: methane with a mass of 224 g entered the decomposition reaction.