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 ) Δ H = − 764 kJ How much methanol, in grams, must be burned to produce 719 kJ of heat?

Answer 1

when -764.0 KJ of heat is involved, 1 mol of CH3OH is reacting
So,
for -7.19*10^2 KJ, mol of CH3OH = -7.19*10^2*1/-764.0 KJ
= 0.9411 mol

Molar mass of CH3OH,
MM = 1*MM(C) + 4*MM(H) + 1*MM(O)
= 1*12.01 + 4*1.008 + 1*16.0
= 32.042 g/mol

use:
mass of CH3OH,
m = number of mol * molar mass
= 0.9411 mol * 32.04 g/mol
= 30.15 g
Answer: 30.1 g