What mass of carbon dioxide is produced from the complete combustion of 7.00×10−3 g of methane?

1 answer

2CH4 + 5O2 ==> 2CO2 + 4H2O
mols CH4 = 0.007/16 = approx 0.00044 but that's an estimate. You need to recalculate to get a more exact answer.
mols CO2 produced = about 0.00044 x (2 mols CO2/2 mols CH4) = about 0.00044
Then grams = mols x molar mass = ? Remember to recalculate everything.