Non-spontaneous reaction and Gibbs Free Energy

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SUMMARY

The discussion centers on the non-spontaneous decomposition of quartz (SiO2) into silicon and oxygen at 25 degrees Celsius, despite a positive standard entropy change (ΔS = +182.02 J/K). The Gibbs Free Energy equation (ΔG = ΔH - TΔS) is crucial for understanding this phenomenon. With ΔH at +910 kJ/mole, the positive enthalpy change outweighs the entropy contribution at this temperature, resulting in a positive ΔG, indicating non-spontaneity. Thus, the reaction does not occur spontaneously under standard conditions.

PREREQUISITES
  • Understanding of Gibbs Free Energy and its equation
  • Knowledge of thermodynamic concepts such as enthalpy (ΔH) and entropy (ΔS)
  • Familiarity with temperature effects on chemical reactions
  • Basic principles of kinetics in chemical reactions
NEXT STEPS
  • Calculate Gibbs Free Energy for various reactions using different ΔH and ΔS values
  • Explore the relationship between temperature and spontaneity in chemical reactions
  • Study the kinetics of the SiO2 decomposition reaction
  • Investigate the implications of non-spontaneous reactions in industrial processes
USEFUL FOR

Chemistry students, thermodynamics researchers, and professionals in chemical engineering seeking to understand reaction spontaneity and thermodynamic principles.

jmm5872
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Quartz, SiO2(s), does not spontaneously decompose to silicon and oxygen at 25 degrees Celsius even though the standard entropy change of the reaction is large and positive (deltaS = +182.02 J/K). Explain why.

I am confused by this one fundamentally because it seems like common sense that quartz doesn't spontaneously turn to solid silicon and oxygen gas at this temp.

Looking at Gibbs Free Energy and the effects of temperature on this it says that if \DeltaH is negative and \DeltaS is positive then the reaction is spontaneous at all temperatures.

I don't understand what concept I am missing.
 
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jmm5872 said:
I don't understand what concept I am missing.

Kinetics
 
SiO2 --> Si + O2
delta H= + 910 KJ/mole ( note kilo joules)
delta S= + 182 J/K mole
T= 298 K

delta G= delta H -T delta S

What you are missing is putting in the correct values and getting the answer.

Kinetics
 
Last edited:

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