Consider the combustion of butane gas:C₄H₁₀(g ) + 13/2O₂(g) → 4CO₂(g) + 5H₂O(g) (b) Calculate ΔG° by two different methods.

Respuesta :

The value of ΔG° (gibbs free energy change) is -2703kj and -2657kj.

Given ,

combustion reaction of butane :

C4H10(g) + 13/2O2 (g) →4CO2(g) + 5H2O(g)

Method-1 :

We know ,

ΔGrxn = sum of ΔG (product ) - sum of ΔG (reactant )

= [4 × (-394.4) + 5×(-228.6) ] - [1×(-16.7)]

ΔGrxn = -2720.6kj

Method-2 :

We know ,

ΔG = ΔH -TΔS

T =298K

Thus , ΔHrxn = sum of ΔH (product ) - sum of ΔH (reactant )

= [4×(-393.5) + 5×(-241.8) ] - [ 1×(-126)]

ΔHrxn = -2657kj

ΔSrxn = sum of ΔS (product ) - sum of ΔS( reactant )

= [ 4×(213.7) + 5×188.7 ] - [ 13/2 ×205 + 1×310 ]

ΔSrxn = 155.8j/K

ΔSrxn = 0.1558kj/K

Thus , ΔG = ΔH - TΔS

= -2657 - ( 298 × 0.1558kj/K )

ΔG = -2720kj

Hence , the value of ΔG is -2703kj .

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