Question

The complete combustion of ethanol, C2H5OH (molar mass = 46.0 g/mol)

C2H5OH(l) + 3O2(g)  2CO2(g) + 3H2O(l) ∆𝐻 = −555 𝑘𝐽

 

What is the enthalpy change for combustion of 15.0 of ethanol?

Answer 1

Knowing that the amount of released heat will be directly proportional to the amount of substance, we will make a proportion. One mole of ethanol upon combustion gives 555 kJ of energy, then we find the amount of ethanol substance in 15 grams: mass of ethanol / molar mass = amount of substance;

$m/M = \nu$

15.0 / 46.0 = 0.326 mol. This means that energy is released:

$Q=$ 555 × 0.326 = 180.97 kJ

$Q= -\Delta H,$ hence the enthalpy is -180.97 kJ.

ANSWER: $\Delta H= -180,97 kJ$