- Physical Chemistry I
Spring 2012, Unique 52135
Lecture Summary, 30 March 2012
thermodynamics is a branch of physical chemistry that is concerned
with connecting macroscopic properties of a system (pressure,
temperature, volume, free energy, etc.). Although we have gone
through this semester without caring about the molecular nature of
our "system," there must be a reason why a collection of atoms and
molecules will display these properties. Stat mech figures out
how properties of individual atoms or molecules combine to create
properties of a system, which is nothing more than a very large
number of atoms or molecules.
All energy is quantized. A collection of atoms or molecules occupies a ladder of energy states. Once a system contains any significant quantity of species, it will not be possible to just count up the number of possible configurations and determine the most likely state. We must use the mathematics of statistics and probability the figure out how the system is most likely configured. As long as we do this correctly, our guess at what the system probably looks like will probably be a pretty good guess.
To do this, we need to impose two constraints on our system. 1) The total number of atoms or molecules cannot change. At any point, we must be able to account for every particle in our system. 2) The total energy of the system cannot change (i.e. we are not doing anything to our system; it's static, sitting doing nothing).
The solution to this problem is expressed by the Boltzmann distribution, which is in your book. We will see how this allows us to connect microscopic to macroscopic properties.