May 10, 2009
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Can someone explain to me the fundamental understanding of why, when two hydrogen atoms for example, release energy when they form a covalent bond? I can't seem to comprehend. Here is my reasoning, please see if this makes any sense of I am simply going in the wrong direction, I would really appreciate this. I am an undergraduate student loving the sciences and have tried figuring this out all night, it is frustrating me:

The kinetic-molecular theory of matter states that all matter consists of tiny particles (everything from atoms, molecules, or ions) which are in constant motion. This means that atoms, molecules, ions, etc. all have kinetic energy associated with them on the microscopic scale known as thermal energy.

I know bond formation between two hydrogen atoms occurs when two atoms (that are moving very high speeds) are stabilized due to the electrostatic attraction-repulsion stability formed between the electrons and protons of the two atoms. This constitutes a chemical bond.

So, did the kinetic energy of the atoms that was once moving really fast, get converted to heat given off to the surroundings, because the bond formation slowed down the thermal energy of the once separated, fast moving atoms??

I am also having a hard time understanding chemical potential energy in a covalent bond. I know that chemical bond formation within a molecules, gives rise to chemical potential energy due to electrostatic attraction-repulsion stability formed between the electrons and protons of the two atoms.

Is potential energy of a chemical system, for example a molecule, visualized as the energy required to counteract the electrostatic force that holds atoms together, i.e the chemical bond?

So, to break a bond we would need to increase the kinetic energy of the individual atoms so that they overcome the the electrostatic interactions that was holding the bond together?

How do you increase the kinetic energy of an individual atom in order to overcome the potential energy of covalent bond in the molecules? They absorb thermal energy from the surroundings, correct?

Thus chemical potential energy is converted to kinetic energy in bond breaking? But in bond formation kinetic energy (thermal energy) of the atoms is converted to heat and/or light?
 

Arctic

PCO Class of 2014
Aug 16, 2009
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It's great that you're making an effort to conceptually understand this concept.

I'll give a simple, direct example that should help although to truly understand a covalent bond requires substantial understanding of quantum mechanics. But you can still understand the basic thermodynamic principles at play without getting too technical.

So, lets say I have two magnets. What happens when I put the magnets together? Well, if I properly align the poles (north-south) then the two magnets will stick to each other. In a sense, you can think of a covalent bond in the same fashion; the atoms become 'stuck' (bonded) to one another. And, just as it takes energy to pull the two magnets apart again (I'm sure you've played with magnets as a kid?) it also takes energy to 'pull' the atoms apart again by splitting the bond. I know it's much easier in this example to see the energy it takes to pull magnets apart than it is to 'see' the energy released when they come together, but rest assured, conservation of energy (i.e. energy cannot be created or destroyed, only converted) applies, i.e. the amount of energy required to pull the magnets apart is equal to the amount of energy given off when they come together.

I do think that you are on the right track with your current line of reasoning. When two hydrogen atoms form a bond, the overall energy level of the two atoms combined decreases (i.e. diatomic hydrogen is significantly more stable than mono-atomic hydrogen, which is why hydrogen is naturally found as a diatomic element). The decrease in energy level caused by forming the bond (which you certainly can think of in terms of the fact that the atoms' freedom to 'jiggle around' has been lowered) needs to be made up for via conservation of energy, so heat (light) will be given off when two hydrogen atoms bond. Conversely, to break a bond between two hydrogen atoms, you need to add heat (light).
 

doc3232

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This is irrelevant to the DAT...you don't need to understand it. Don't waste your time on this. Just know it without understanding it.
 
May 10, 2009
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Thanks for the reply, Arctic


This is irrelevant to the DAT...you don't need to understand it. Don't waste your time on this. Just know it without understanding it.
You're right, but I prefer to learn things from a fundamental perspective, which when mastered, seems to make learning everything else much easier.