- Principles of Chemistry I: Honors
Fall 2012, Unique 51390
Lecture Summary, 4 December 2012
Law of Thermodynamics: Chemical
thermodynamics is the study of the flow and conversion of energy
in chemical systems. Thermodynamics is focused on
understanding the behavior of a system, and the flow of
energy between the system and its surroundings.
We talked about three kinds of systems: open, closed, and
isolated. In this class we will focus only only closed
To understand how energy is exchanged between system and surroundings, we need to be able to understand how the system changes from an initial to a final state. This involves moving along a path, which is associated with two new path functions: work and heat. The magnitude of these depends on the particular path taken to get from an initial to a final state.
w = -Pext(deltaV)
qv = nCv(deltaT)
where Cv is a heat capacity measured at constant volume, and is a characteristic property of the material.
Although both heat and work are path functions, their sum is a state function, called internal energy, U. For any change from one state to another, the change in internal energy is equal to the sum of the heat and work experienced along that path:
(deltaU) = q + w
This is a statement of the 1st law of thermodynamics.
At constant pressure, this equation can be manipulated to give a new state function, called enthalpy:
(deltaH) = (deltaU) + P(deltaV) = nCv(deltaT) + nR(deltaT) = nCp(deltaT)
where Cp = Cv + R.