chemistry with calorimetry problem !

Question

When methanol, CH₃OH is burned in the presence of oxygen gas, O₂ a large amount of heat energy is released. For this reason, it is often used as a fuel in high performance racing cars. The combustion of methanol has the balanced, thermochemical equation

CH₃OH (g) + 3/2 O₂( g) → CO₂ (g) + 2 H₂O (l)



How much methanol, in grams, must be burned to produce 995 kJ of heat?

Answer 1

I googled to find the heat of combustion of methanol and found it to be -715 kJ/mol. Inverting this number, you get 1/-7.15 mol/kJ. Multiply by the 995 kJ in the problem to get the number of moles needed to get that much heat evolved. This turns out to be 139.2 moles.

As the molecular weight of methanol is close to 32 g/mol, the number of grams is

32 g/mol x 139.2 mols = 4450 g to 3 sig figs.