exo vs. endo speed of reaction

[joonkimdds]

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which is faster?

Endothermic reaction = heat is added and increase in temperature speeds up the reaction so my initial guess was that endothermic is faster.

However, the correct answer is that exo is faster.

Could someone explain this to me?

 

[nze82]

which is faster?

Endothermic reaction = heat is added and increase in temperature speeds up the reaction so my initial guess was that endothermic is faster.

However, the correct answer is that exo is faster.

Could someone explain this to me?

Here's how I see it...
Endothermic require energy in form of heat to climb an energy barrier before they even start; whereas, exothermic reactions are spontaneous and they don't need any energy input to overcome any significant energy barriers. Thus, they occur much faster than endothermic ones.

 

[TedyBearSuicide]

Exothermic reaction have negative change of Gibbs free energy, so they release energy in form of heat. Thus making them spontaneous reactions.

Exothermic reactions: Release energy (faster)
Endothermic reactions: Need energy (slower)

 

[Shinpe]

which is faster?

Endothermic reaction = heat is added and increase in temperature speeds up the reaction so my initial guess was that endothermic is faster.

However, the correct answer is that exo is faster.

Could someone explain this to me?

Is the question just "are exothermic reactions faster or endothermic reactions?"

I think there's gotta be more to it. I'm pretty sure you can't say a reactions is faster/slower just because it's exo/endo, unless they're giving you some other information too, like info about the temp. I'd think.... I could be wrong ....

What determines the rate of rxn is the activation energy, and that I can't imagine it being a general function of whether a rxn is exo/endo.

One thing that could make sense though is that when exothermic reactions occur, they release hit, right? so let's say you have 10 reactants, you have enough energy to push 2 of them over the activation barrier, these 2 will then form products and release heat which can send some other molecules over the barrier, and then form a chain like that. But endo wouldn't have that, all the activation energy will have to be supplied from outside.

And again, exothermic/endothermic has nothing to do with spontaneity (well you know). that would be exergonic/endergonic.

 

[Shinpe]

But I still don't think you could say ANY exo rxn is faster than ANY endo rxn. There might be a general trend though. ......

 

[dentrilla]

Here's how I see it...
Endothermic require energy in form of heat to climb an energy barrier before they even start; whereas, exothermic reactions are spontaneous and they don't need any energy input to overcome any significant energy barriers. Thus, they occur much faster than endothermic ones.

wrong.. both require activation energy. As you can see with this diagram, green is endothermic and blue is exothermic. Both have Ea's. Just because this particular example shows the exothermic with a lower Ea (and thus faster reaction speed, assuming they're both given the same energy) doesn't mean this is always the case. You could easily draw an exothermic reaction with a larger Ea then the green endothermic rxn shown here.

 

[T00thFa1ry]

dentrilla, what compound is that on your energy diagram?