Question

calculate the change in free energy as ethanol burns under standard conditions

Practice 12.6 Calculating AGPxn Using Appropriate AG Values . Using the appropriate standard free energy of formation values calculate the change in free energy as ethanol burns under standard conditions. CH,CH,OH(0) + 3 O2(g) + 2 CO2(g) + 3 H 0(0)

Answer 1

Balanced reaction is

CH₃CH₃OH_(l) + 3O_2(g)    $\rightarrow$ 2CO_2(g) + 3H₂O_(l)

Standard free energy of formation

∆G⁰_f CH₃CH₃OH_(l)  = -174.8 KJ / mol

∆G⁰_f O2_(g)  = 0 KJ / mol

∆G⁰_f CO_2(g)  = -394.39 KJ / mol

∆G⁰_f H₂O_(l)  = -337.14 KJ / mol

we know the equation

∆G⁰_rxn = ∑∆G⁰_{f (product)} -   ∑∆G⁰_{f (reactant)}

∆G⁰_rxn = [ 2( ∆G⁰_f CO_2(g) ) + 3( ∆G⁰_f H₂O_(l) ) ] - [ ( ∆G⁰_f CH₃CH₃OH_(l) ) + 3 ( ∆G⁰_f O2_(g) ) ]

substitute the value

∆G⁰_rxn = [ ( 2 X (-394.39 KJ/mol)) + ( 3 X (-237.14 KJ/mol))] - [ ( -174.8KJ/mol) + ( 3 X 0KJ/mol) ]

∆G⁰_rxn = [-1500.2 KJ/mol] - [-174.8 KJ/mol]

∆G⁰_rxn = [-1500.2 KJ/mol] + [174.8 KJ/mol]

∆G⁰_rxn = -1325.2 KJ