How many kilojoules of Gibbs Free Energy

Question

The combustion of ethane by the following unbalanced chemical reaction:

a C2H6(g) + b O2(g) --> c CO2(g) + d H2O(g)

How many kilojoules of Gibb's Free Energy are liberated by burning 21.624g of ethane in excess oxygen?

Substance ΔG°f(kJ/mol)

C2H6(g) -32.04

O2(g) 0

CO2(g) -394.36

H2O(g) -228.59

Answer 1

2C₂H₆(g) + 7O₂(g) ==> 4CO₂(g) + 6H₂O(g) ... BALANCED EQUATION

2x-32.04.......0..............4x-394.36....6x-228.59

∑products = -1577.44 + -1371.54 = -2948.98 kJ

∑reactants = -64.08 + 0 = -64.08 kJ

∆Grxn = ∑products - ∑reactants

∆Grxn = -2948.98 kJ + 64.08 kJ

∆Grxn = -2884.9 kJ ... This is for the reaction as written, i.e. for 2 moles of ethane (C2H6)

For 21.624 g ethane, we will have the following:

21.624 g C2H6 x 1 mol C2H6 / 30.069 g = 0.7191 mol

2884.9 kJ / 2 mol ethane x 0.7191 mol ethane = 2075 kJ of heat energy liberated

(be sure to check the math)