CH301H - Principles of Chemistry I: Honors
Fall 2015, Unique 49310

Lecture Summary, 19 November 2015


1st 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 systems.

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.