The U.S. government requires automobile fuels to contain a renewable component. Fermentation of glucose from corn yields ethanol, which is added to gasoline to fulfill this requirement:C₆H₁₂O₆(s) → 2C₂H₅OH(l) + 2CO₂(g) Calculate ΔH°, ΔS°, and ΔG° for the reaction at 25°C. Is the spontaneity of this reaction dependent on T? Explain.

Respuesta :

ΔH° = -67.9 kJ

ΔS° = 536.7 J/K = 0.5367 kJ/K

ΔG° = -227.8 kJ

The spontaneity of this reaction dependent on T .

Given ,

Temperature = 25.0 °C=298K

ΔH°f(glucose) = - 1274.5 kJ/ mol

ΔH°f(C2H5OH) = -277.7 kJ/mol

ΔH°f(CO2) = -393.5 kJ/mol

S°(glucose) = 212.1 J/ K)

S°(C2H5OH) = 160.7 J/K

S°(CO2) = 213.7 J/K

The given equation is ,

C6H12O6(s) → 2 C2H5OH(l) + 2 CO2(g)

As we know ,

ΔH°= ΔH°(product ) - ΔH°(reactant )

ΔH° = 2*ΔH°f(C2H5OH) + 2ΔH°f(CO2) - ΔH°f(glucose)

ΔH° = 2*(-277.7 kJ) + 2*(-393.5 kJ) - (-1274.5 kJ)

ΔH° = -555.4 kJ + (-787 kJ) +1274.5 kJ)

ΔH° = -67.9 kj

As we know ,

ΔS°=ΔS°(product ) - ΔS°(reactant )

ΔS° = 2*S°(C2H5OH)  + 2*S°(CO2) - S°(glucose)

ΔS° = 2*(160.7 J/K) + 2(213.7 J/K) - 212.1 J/K

ΔS° = 321.4 + 427.4 J/K - 212.1 J/K

ΔS° = 536.7 J/K = 0.5367 kJ/K

As we know ,

ΔG° =ΔH° - T×ΔS°

ΔG° = -67.9 kJ - 298K * 0.5367 kJ/K

ΔG° = -227.8 kJ

Since ΔS° is positive and  ΔH° is negative, ΔG° will be negative.

A negative ΔG° means the reaction is spontaneous and it is dependent on T .

Learn more about spontaneous reaction here :

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