CHAPTER
122 ❯
9
Thermodynamics
IN THIS CHAPTER
Summary: Thermodynamics is the study of heat and its transformations.
Thermochemistry is the part of thermodynamics that deals with changes in heat
that take place during chemical processes. We will be describing energy changes
in this chapter. Energy can be of two types: kinetic or potential. Kinetic energy is
energy of motion, while potential energy is stored energy. Energy can be con-
verted from one form to another but, unless a nuclear reaction occurs, energy
cannot be created or destroyed (Law of Conservation of Energy). We will discuss
energy exchanges between a system and the surroundings. The system is that part
of the universe that we are studying. It may be a beaker or it may be Earth. The sur-
roundings are the rest of the universe.
The most common units of energy used in the study of thermodynamics are the
joule and the calorie. The joule (J) is defined as:
1 J = 1 kg m^2 /s^2
The calorie was originally defined as the amount of energy needed to raise the
temperature of 1 g of water 1°C. Now it is defined in terms of its relationship to the
joule:
1 cal = 4.184 J
It is important to realize that this is not the same calorie that is commonly associated
with food and diets. That is the nutritional Calorie, Cal, which is really a kilocalorie
(1 Cal = 1,000 cal).Keywords and Equations
S° = standard entropy H° = standard enthalpy
G° = standard free energy q = heat
c = specific heat capacity Cp = molar heat capacity at constant pressure
DS° = S S° products - S S° reactantsKEY IDEAKEY IDEA