Chemistry question Help

Question

Met‎hanol, CH₃OH (‎molar mass: 32.042 g/mol), reacts‎ with O₂ and can be used‎ as fuel according to the reaction below (ΔH_rxn = –764 kJ/mol CH₃OH). What mass of O₂ (molar mass: 31.998 g/mol) is consumed when 432 kJ of heat is given off?

CH₃OH + 32O₂  ➜ CO₂ + 2H₂O

Answer 1

The equation as presented is incorrect, and not balanced. Here is the correctly balanced equation

2CH₃OH + 3O₂  ➜ 2CO₂ + 4H₂O ... balanced equation for combustion of CH₃OH

For 2 mol CH₃OH and 3 mols O₂, 764 kJ of heat energy are given off. So, all we need to do is find out how many mols of O₂ are used when 432 kJ of energy are given off.

432 kJ x 3 mols O2 / 764 kJ = 1.696 mols O₂

mass of O₂ = 1.696 mols O2 x 31.998 g/mol = 54.3 g O₂ (3 sig. figs.)