Question

Determine the mass (in grams) of oxygen that will result in a change in energy of -93.02 kJ when oxygen reacts with excess ethanol according to the following balanced thermochemical equation:



C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)  ΔH_r° = -1367.51 kJ



Report your answer to three significant figures.

Answer 1

From reaction,
when 3 moles of O2 reacts, energy change = -1367.51 KJ

For energy change = -93.02 KJ,
number of moles of O2 required = 3*93.02 / 1367.51 = 0.204 mol

Molar mass of O2= 32 g/mol

Mass of O2 = molar mass * number of moles
                        = 32 * 0.204
                        = 6.53 g
Answer: 6.53 g