general chemistry 1

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) + 2H2O(l)

Δ𝐻= −764 kJ

How much methanol, in grams, must be burned to produce 791 kJ of heat?

answer: mass=_____g

Answer 1

(-791 kJ) × (1 mol rxn / -764 kJ)=1.0353 mol rxn

By the coefficients:

1 mol rxn = 1 mol CH3OH

Therefore, 1.0353 mol CH3OH is present

Use the molar mass of CH3OH:

1.0353 mol (32.042 g / 1 mol)=33.17 g CH3OH