-4
$\begingroup$

If atoms and molecules aim for stability and equilibrium, then why do they feel the need to revert back into their original state once they have already found stability?

Example: $\ce{I2 + H2 \to 2HI}$

What causes reversible reactions to exist?

Because "it is generally said that reactants react so that they can achieve a lower energy state."

Then why does a reversible reaction occur in the first place? Since turning reactants into products increases their energy - an undesirable effect from the point of view of reacting molecules....

What causes product atoms to naturally revert back into the reactant state?

Improve this question
$\endgroup$
2
  • $\begingroup$ Atoms and molecules don't "feel" anything. They lack volition. So instead of "why do they feel the need to revert " I would ask "why do they revert" ..... $\endgroup$
    – Buck Thorn ♦
    Commented Jun 6 at 10:15
  • $\begingroup$ Well, balls tend to roll down the hill, but if you keep hitting one with another, they can go back. For some reason you don't account for thermal energy in your picture. It's like your potential energy surface was some black hole instead of gentle hills. $\endgroup$
    – Mithoron
    Commented Jun 6 at 12:18

1 Answer 1

Reset to default
1
$\begingroup$

  1. Atoms and molecules move constantly -- that is the basis of the kinetic theory of heat.

  2. The Maxwell-Boltzmann distribution shows that not all particles move at the same speed, i.e., they vary in energy. Even at moderate temperatures, a few particles may have much greater energy than the average.

  3. Though the reactants produce a product that is more stable than the original, there are likely some molecules that provide sufficient energy to make the product revert to the reactants.

    Some reactions are strongly biased in one direction. E.G., $\ce{Fe2O3 + 2Al -> Al2O3 + 2Fe}$. At room temperature, it is unlikely that more than a few molecules would revert, and then they would be very likely to revert again to the more stable aluminum oxide and iron, but at very high temperatures, the reaction can run backwards.

    Some reactions are readily reversible near room temperature, as one species become more stable than another. A classic example is $\ce{NO2 <-> N2O4}$, such as shown in this video by Jim Schneider.

Improve this answer
$\endgroup$
6
  • $\begingroup$ So some molecules provide sufficient energy to make the product revert to reactant state, what is the origin of this energy and why and how is this energy causing this revert? $\endgroup$
    – Yoojin
    Commented Jun 6 at 5:12
  • $\begingroup$ I understand your point, but I'm still confused as to how this 'energy' can cause such. could you please explain it in molecular level in detail? $\endgroup$
    – Yoojin
    Commented Jun 6 at 9:03
  • $\begingroup$ @Yoojin, read 1. and 2. View the references. If you don't understand those links, ask a specific question. $\endgroup$
    – DrMoishe Pippik
    Commented Jun 6 at 17:02
  • $\begingroup$ I see. I have a question regarding the video by Jim Schneider, when the tube was placed from the hot water container to the cold water container, more N204 formed in a short time span as the visible changes could be observed as the color of tube lightened. I can only conclude that cold temperature favors the formation of N2O4 as equilibrium shifts towards right. But in order to go from brown to colorless, bonds need to be formed as N2O4 is the product. But in cold temperature, collision's frequency decreases thus reaction rate decreases. So how does the color change occurred? $\endgroup$
    – Yoojin
    Commented Jun 7 at 4:17
  • $\begingroup$ "Decrease"does not mean "cease". $\endgroup$
    – DrMoishe Pippik
    Commented Jun 7 at 15:11

Not the answer you're looking for? Browse other questions tagged or ask your own question.