Why is Reaction Spontaneousity Not Occuring at 298K?

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SUMMARY

The discussion centers on the spontaneity of a combustion reaction at 298 K, where 15 moles of gas reactants yield only 9 moles of gas products. The key conclusion is that the Gibbs free energy change is positive, indicating that the reaction is not spontaneous despite being thermodynamically favorable under certain conditions. The significant decrease in gas moles leads to a pressure change that affects the enthalpy, which is negative but insufficient to drive the reaction forward. Additionally, external factors such as activation energy must be considered, as evidenced by gasoline and oxygen not reacting spontaneously in everyday conditions.

PREREQUISITES
  • Understanding of Gibbs free energy and its role in chemical spontaneity
  • Knowledge of enthalpy and its behavior under constant pressure conditions
  • Familiarity with the ideal gas law and its implications for gas reactions
  • Concept of activation energy and its effect on reaction rates
NEXT STEPS
  • Study the principles of Gibbs free energy and its calculations in chemical reactions
  • Learn about the ideal gas law and its applications in predicting reaction behavior
  • Explore the concept of activation energy and its significance in reaction kinetics
  • Investigate the conditions under which combustion reactions become spontaneous
USEFUL FOR

Chemistry students, educators, and professionals interested in thermodynamics, chemical kinetics, and reaction mechanisms.

LordVoldemort
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Homework Statement


Sorry - this was on a test I took today, so I don't remember it exactly. A reaction (I believe a combustion reaction) is known to be spontaneous at 298 K. When the reactants are placed are placed into a container, no reaction occurs. Why? Info: The reactant side had 15 moles of gas while the products had only 9 (see next section).

2. The attempt at a solution
I had to guess, so I reasoned that a reaction is spontaneous iff the Gibbs free energy is lowered. The fact that it is not spontaneous means that the Gibbs energy change was positive. I recalled that enthalpy assumes constant pressure, and in a container, a change from 15 moles of gas to 9 moles would mean a large pressure change, so I guessed that this would cause the enthalpy (which was negative) to decrease in magnitude.
 
Physics news on Phys.org
If no reaction has occurred, can you conclude that the reaction is not spontaneous? Are there other requirements for a chemical reaction to occur? Gasoline and oxygen combine spontaneously at room temperature to form carbon dioxide and water. Yet, people's cars are not bursting into flames. Why is this?
 

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