Why is Reaction Spontaneousity Not Occuring at 298K?

In summary, the conversation discusses a spontaneous reaction at 298 K that does not occur when the reactants are placed into a container. The reason for this is that the Gibbs free energy change was positive, meaning the reaction is not spontaneous. The enthalpy change may also play a role, as the pressure change from 15 moles of gas to 9 moles may cause the enthalpy to decrease in magnitude. Other requirements for a reaction to occur are also mentioned, such as the presence of gasoline and oxygen, but the lack of spontaneous combustion in cars.
  • #1
LordVoldemort
1
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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.
 
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  • #2
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?
 

FAQ: Why is Reaction Spontaneousity Not Occuring at 298K?

Why is reaction spontaneity not occurring at 298K?

At 298K, a reaction may not be spontaneous because the reactants may not have enough energy to overcome the activation energy barrier. This means that the reaction will not occur without an external source of energy.

What is the significance of 298K in relation to reaction spontaneity?

298K is a commonly used temperature in chemistry experiments and is also known as standard temperature. At this temperature, reactions may or may not be spontaneous depending on the energy of the reactants.

Can a reaction be spontaneous at 298K?

Yes, a reaction can be spontaneous at 298K if the reaction is exothermic and the products have lower energy than the reactants. This means that the reaction can release enough energy to overcome the activation energy barrier and proceed without any external energy source.

How does temperature affect reaction spontaneity?

Temperature plays a crucial role in determining the spontaneity of a reaction. As temperature increases, so does the energy level of the reactants. This makes it easier for the reactants to overcome the activation energy barrier and for the reaction to become spontaneous.

Are there any other factors besides temperature that can affect reaction spontaneity?

Yes, besides temperature, other factors that can affect reaction spontaneity include the concentration of reactants, pressure, and the presence of catalysts. These factors can alter the energy of the reactants and make it easier or harder for the reaction to proceed spontaneously.

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