Oxyacetylene (C2H2)(ΔH=227.4kJ/mole) combusts in oxygen (ΔH= 0.0 kJ/mole) to produce carbon dioxide ΔH= -393.5 kJ/mole) and water . Calculate ΔH for the reaction in kJ.

Answer 1

First, write the balanced equation for the reaction taking place:

2C2H2(g) + 5O2(g) ==> 4CO2(g) + 2H2O(g) ... balanced reaction for combustion of acetylene

227.4.............0................-393.5.......-241.8......∆Hf values in kJ/mol (I looked up a value for H2O gas)

∆Hrxn = ∑n∆H products - ∑n∆H reactants

∆Hrxn = [(2 x -241.8) + (4 x -393.5] - [(2 x 227.4) + 0] = -2057.2 - 454.8

∆Hrxn = -2512 kJ