Spontaneous reactions require activation energy?

In summary: Yes, it requires activation energy - but so low, that thermal motion of the molecules at room temperature is enough.
  • #1
ldv1452
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0
"Spontaneous" reactions require activation energy?

To my understanding reactions are considered "spontaenous" if they require no additional energy for the reaction to occur. However, they require activation energy. Why is activation energy not considered "additional energy?" The term "spontaneous" doesn't seem to hold its intuitive meaning under this explanation.
 
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  • #2


ldv1452 said:
To my understanding reactions are considered "spontaenous" if they require no additional energy for the reaction to occur. However, they require activation energy. Why is activation energy not considered "additional energy?" The term "spontaneous" doesn't seem to hold its intuitive meaning under this explanation.

Spontaneous - at room temperature?
 
  • #3


DaveC426913 said:
Spontaneous - at room temperature?

Well let's say we take a reaction at room temperature for example. If it is considered "spontaneous" at room temperature doesn't it still require activation energy?
 
  • #4


Yes, it requires activation energy - but so low, that thermal motion of the molecules at room temperature is enough.
 
  • #5


This is what I was hinting at. A little too oblique I guess.
 
  • #6


Borek said:
Yes, it requires activation energy - but so low, that thermal motion of the molecules at room temperature is enough.

So would it be correct to say that a "spontaenous" reaction is one where the activation energy is already available in the system as heat (thermal) energy?
 
  • #7


Something like that.
 
  • #8


It really depends on how you define a "spontaneous" reaction. Most chemistry textbooks will define a "spontaneous" reaction as what I will call a thermodynamically spontaneous reaction. In these reactions, the sole requirement is that ΔG < 0. For these reactions, the reactions occur without a NET addition of energy to the system. A good example here would be burning gasoline. You need to add energy in the form of a spark, but the energy you get out is much greater than the activation energy you provide.

This definition, however, does not match the colloquial definition of "spontaneous." For example, the conversion of diamond to carbon dioxide is thermodynamically spontaneous. However, because the activation energy is so high, the reaction almost never happens at room temperature (hence, diamonds are forever and we don't need to worry about them "spontaneously" evaporating).
 
  • #9


Ygggdrasil said:
It really depends on how you define a "spontaneous" reaction. Most chemistry textbooks will define a "spontaneous" reaction as what I will call a thermodynamically spontaneous reaction. In these reactions, the sole requirement is that ΔG < 0. For these reactions, the reactions occur without a NET addition of energy to the system. A good example here would be burning gasoline. You need to add energy in the form of a spark, but the energy you get out is much greater than the activation energy you provide.

This definition, however, does not match the colloquial definition of "spontaneous." For example, the conversion of diamond to carbon dioxide is thermodynamically spontaneous. However, because the activation energy is so high, the reaction almost never happens at room temperature (hence, diamonds are forever and we don't need to worry about them "spontaneously" evaporating).

Good explanation. This makes more sense now. It would make life easier if words were used that didnt have such strongly ingrained colloquial definitions.
 

What is a spontaneous reaction?

A spontaneous reaction is a chemical reaction that occurs without any outside influence and releases energy. It occurs naturally and does not require any external energy source to start or maintain the reaction.

What is activation energy?

Activation energy is the minimum amount of energy required to start a chemical reaction. It is the energy needed to break the bonds of the reactants and initiate the formation of new products.

Why do spontaneous reactions require activation energy?

Spontaneous reactions still require activation energy because even though they occur naturally, they still involve the breaking and forming of chemical bonds. Activation energy is needed to overcome the energy barrier and initiate the reaction.

How does temperature affect activation energy?

An increase in temperature can lower the amount of activation energy required for a chemical reaction to occur. This is because higher temperatures provide more energy to molecules, making it easier for them to overcome the energy barrier and start the reaction.

Can activation energy be negative?

No, activation energy cannot be negative. It is always a positive value as it represents the minimum amount of energy required to start a chemical reaction. If the value of activation energy were negative, it would mean that the reaction could occur without any energy input, which is not possible.

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