Why chemical reactions happens?

  • #1

Main Question or Discussion Point

We do know that in the process of chemical reaction, atoms or molecules come closer, form bonds and get stabilized by sharing or donating electrons, thus filling the valance shell of atoms. But why do they want to get stabilized?.
 

Answers and Replies

  • #2
Ygggdrasil
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Everything is driven by the second law of thermodynamics. First, this principle drives the system to increase its own entropy. Second, systems want to achieve a low state of potential energy as this allows the system to release heat, which increases the entropy of the surroundings.
 
  • #3
Everything is driven by the second law of thermodynamics. First, this principle drives the system to increase its own entropy. Second, systems want to achieve a low state of potential energy as this allows the system to release heat, which increases the entropy of the surroundings.
But, why there is a law ,i.e, law of thermodynamics, to reduce energy or increase entropy?.
 
  • #4
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But, why there is a law ,i.e, law of thermodynamics, to reduce energy or increase entropy?.
only god knows
 
  • #5
only god knows
is there a scientific explanation?
 
  • #6
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is there a scientific explanation?
I don't think so, the basic laws of thermodynamics are starting principles from which everything else is derived. They are experimentally determined, and I don't think anyone can tell you why things are as they are.

You can look at entropy as the arrow of time, the law of conservation of energy tells you things can happen in any direction of time. Like when you drop an egg, the egg is shattered, but according to conservation of energy it can easily come back together from the ground right back in your hands. The law of entropy tells you, it can only go in one direction, you drop it, it shatters, and the opposite can't happen.
 
  • #7
I do understand and appreciate the basic scientific laws. I dont have a problem in imagining that complex molecules came together and started evolving through generations, and reached the stage where we see complex life forms. Basis of the evolution is the chemical reactions. But why atoms or molecules wants to reduce energy or increase entropy. Who did design the natural laws?.
 
  • #8
Borek
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Who did design the natural laws?.
Whether you ask for "who" or whether you ask for "why" - sooner or later you will get to the level at which answer is "we don't know". Doesn't mean we will never know.

I don't like "who" question, as it suggests existence of designer. We know nothing that suggests its existence.

See this video, it doesn't address precisely your question, but it does tell something about the problem in general:

 
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  • #9
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I do understand and appreciate the basic scientific laws. I dont have a problem in imagining that complex molecules came together and started evolving through generations, and reached the stage where we see complex life forms. Basis of the evolution is the chemical reactions. But why atoms or molecules wants to reduce energy or increase entropy. Who did design the natural laws?.
The only answer I can come up with to why they want to increase entropy are the basic laws of thermodynamics, which says nature will always tend to maximise the total entropy (including surroundings), unless you put energy in to decrease entropy. I have no idea who designed the natural laws, god?
 
  • #11
epenguin
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Part 1
reactions of a molecule

I don't mean to seem philistine but this is not a question about chemistry. I do not mean that it is not a proper question, but it is a more general question about natural physical laws - whatever the general answer also applies in chemistry.

Why a individual molecule reacts you could say is because there are electrical forces between that parts of a molecule and between one molecule and another that push atoms to go from one molecule to another. That forces push an atom in a certain pathway, or that potential energy diminishes along that pathway overall is saying the same thing in different ways, though physicists and chemists tend to prefer the second.

The nature of these forces is all electrostatic - nothing but Coulomb's law. Except the dynamics within which the forces operate is quantum mechanical which makes it all more complicated and unobvious. Very important within that is a principle called the exclusion principle which is not exactly a force, but makes electrons get away from each other and so build atoms with shapes of electric charge distribution and that get bigger the more electrons there are, roughly speaking.

The principles can be stated very briefly (no doubt better than I have). How that works out in actually explaining any phenomena, and even what it really means, is what your big textbooks are about
.
If you ask why the Coulomb law you are out of chemistry and into at least quantum field theory I think, or hifalutin physics anyway. If you ask why the quantum laws you are into even more fundamental physics, I don't know if there is an answer for now. The chemist is forced to just accept those laws as if he is dragged into that fundamental direction he will never get out of it to do any chemistry, and like sewage disposal someone has to do it (and it has its own interest, and most science is like that). Within those limits the physical chemist can rather well for example 'fundamentally' explain the hydrogen bond, which is key to the functioning of DNA, RNA and proteins - then the biologist has to accept likewise on trust a dumbed down version of that.
 
  • #12
So it looks like a mystery that there are fundamental laws which control everything!.
 
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  • #13
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Yep, you kan keep asking why untill you reach the fundamental laws, like Maxwell's laws, entropy, conservation of energy and so on
 
  • #14
Borek
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So it looks like a mystery that there are fundamental laws which controls everything!.
Cheap sensationalism. So far we discovered and explained thousands of laws, there is no reason to think those undiscovered and unexplained are more special.
 
  • #15
Let me put it this way:
So it looks like a mystery 'now' that there are fundamental laws which controls everything!. In future we may find it.
 
  • #16
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You can only find deeper fundamental laws, but you will never be able to explain why these laws exist. In that sense it will always stay a mystery
 
  • #17
Ygggdrasil
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But, why there is a law ,i.e, law of thermodynamics, to reduce energy or increase entropy?.
only god knows
Well, then apparently I am god.

The second law of thermodynamics is essentially a statement that the universe will tend to the most likely outcome. Imagine having 100 coins in a box all facing heads up. If you shake the box, the coins will obviously move toward 50 coins showing heads and 50 coins showing tails. The second law of thermodynamics essentially takes this tendency for systems to move toward the most probable state and introduces a quantity called entropy to quantify this tendency.
 
  • #18
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Can you also tell us why this tendency exists?
 
  • #19
Ygggdrasil
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Math.

There is exactly one microstate where all coins are facing heads up. There are 100!/(2*50!) ~ 10^93 microstates where the coins show 50 heads and 50 tails. 10^93 > 1.
 
  • #20
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That's just going in circles, math can never explain why things are as they are. You can make lots of mathematical correct theories, but only experiment decides which one is the correct one.
 
  • #21
Math.

There is exactly one microstate where all coins are facing heads up. There are 100!/(2*50!) ~ 10^93 microstates where the coins show 50 heads and 50 tails. 10^93 > 1.
So did u mean to say that there are more microstates associated with a molecule, than with a state where the atoms are separated?
 
  • #22
epenguin
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Ygggdrasil's answer was going to be my Part 2. There is something that is completely explained without needing a further law. (Almost).

I read that for Einstein the 2nd law was a model for the ideal of complete explanation he sought. And of course some of his best work was statistical mechanics.
 
  • #23
Ygggdrasil
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So did u mean to say that there are more microstates associated with a molecule, than with a state where the atoms are separated?
The molecule itself will have a lower entropy than the two lone atoms (i.e. a two atom system has more microstates available to it than a diatomic molecule). However, the second law does not state that the entropy of the system must increase, but it states that the entropy of the universe (the system + surroundings) must increase. Therefore, the reaction can occur if the entropy loss of the system is offset by the entropy gained by the surroundings. As I mentioned before, the surroundings gain entropy when the reaction releases heat. You can think of this as the energy having more microstates available to it in the surroundings than when confined within the system.

So, if the reaction releases enough heat to offset the entropy lost by binding the atoms together, then yes, the universe will have gained entropy (because of the conversion of chemical potential energy into heat).
 

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