Just treat the 82.2 kJ as a product of the reaction and use stoichiometry to found out how many moles of methane were used like so...
82.2kJ x 2mol CH4/252.8 kJ = ?
Then just multiply by the molar mass of methane (about 16.042g) to find how many grams of methane gas are produced from the reaction.
2CH3OH(g)→2CH4(g)+O2(g)ΔH=+252.8kJ
For a given sample of CH3OH, the enthalpy change during the reaction is 82.2kJ . How many grams of methane gas are produced?
3 answers
10.4 grams
Thank you!