mixed stoichiometry

Question

How many moles of oxygen gas are required to completely combust 35.9g of methane gas (CH4).

Answer 1

As with all stoichiometry problems, you must write a balanced equation first:

CH_4(g) + 2 O_2(g) → CO_2(g) + 2 H₂O_(g)

(2 mol O₂/1 mol CH₄) (1 mol CH₄/16.0 g CH₄) 35.9 g CH₄ = 0.891 nol O₂