Hi all,

 

I'm trying to make sense of this...why would molecules prefer to be at a lower energy state (more stable) if the universe prefers to be at a state of disorder?

 

Thanks

The direction of natural evolution is to spread energy as evenly as possible among the accessible means of energy storage. (That's approximately the meaning of entropy).

 

If you consider the electronic states in most small molecules, they are well separated, by several eV. Other means to store energy offer a cheaper entry ticket: rotations are ine the meV range or less, vibrations a bit under 1eV.

 

Our usual room temperature is 26meV; at equilibrium, each means of energy storage receives about as much. It implies that rotations store 26meV each, vibrations can store heat in some molecules (especially solids), but higher electronic states are not populated.

 

QM modifies a bit the statistics, but the result stands that at 26meV temperature, electronic states at 5eV over the ground state are empty. Their probability of occupation resembles exp(-5/0.026) which is zero for practical purposes. In fact, the "entry ticket" make these means store far less energy than 26meV each, so what spread evenly is the temperature, better than the energy.

 

"Disorder" is misleading; even spreading of energy is easier to understand, even temperature (or Fermi level, or Gibbs energy) more accurate.

Thanks for the explanation the usage of disorder is misleading and i have herd it used so many times. But when you think of energy being spread or shared among atoms to lower its overall energy state I can see why atoms decide to get together.

 

Thanks