Chapter 2 - Work, heat, internal energy, and enthalpy

Abstract

The concern is mainly with internal energy, heat, work, and the first law of thermodynamics. Mathematical statements are given for the system and surroundings, the system alone when the system does work on the surroundings, or against constant external pressure. The relationships among the change in the internal energy, work, and heat for isothermal expansion of an ideal gas and real gas are examined. First, when the expansion takes place: into the vacuum, against constant pressure (irreversible), or against changing external pressure (reversible). The molar heat of vaporization and the consequence of the isothermal liquid vaporization, heating a substance at constant volume, and the adiabatic system are studied. Useful relationships among pressure, volume, and temperature for adiabatic change are also examined. The molar change in the internal energy for a chemical reaction is explored. Then we show how to calculate bond enthalpy, and types of chemical and physical enthalpy changes, e.g., enthalpy of solution of solid compound, enthalpy of neutralization, enthalpy of precipitation, enthalpy of combustion, and enthalpy of formation. Next, the basis of the thermochemistry, law of Lavoisier, Laplace, Hess' Law, the heat of formation, mathematic statement for enthalpy, at a constant temperature, and constant pressure are developed. Emphasis is also placed on the correlation between enthalpy and temperature change, heat capacity and enthalpy, constant pressure and constant volume heat capacities, heat capacity and degree of freedom, and finally between heat capacity and reaction enthalpy. Total and partial derivatives with respect to the temperature, pressure, or volume are examined and used to understand the internal pressure and internal energy. Finally, we introduce the Joule-Thompson effect, define the Joule-Thomson coefficient, calorimetry, and bomb calorimeter.