This preview shows pages 1–2. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: 1 5.1 THE NATURE OF THERMODYNAMICS Thermodynamics is concerned with the relationship between the energy changes that occur in chemical and physical processes. In effect, the laws of thermodynamics are the embodiment of the totality of the experimental facts concerning energy changes that occur in nature. The vast, diverse body of experimental facts concerning these energy changes are summarized in the statements of the three laws of thermodynamics. These can be used to predict the direction in which a process would proceed. Thus this science is of great importance to the chemist, since it can predict whether or not a chemical reaction will proceed spontaneously from a knowledge of the thermodynamic properties of the reactants and products. If thermodynamics tells us that a prospective reaction is favorable, then we are on a safe ground to try to find the proper experimental conditions to make the reaction proceed. For example, when gaseous H 2 and O 2 are mixed, thermodynamics tells us that H 2 O should be formed, since H 2 O is more energetically stable than H 2 and O 2. It is a well-known fact that at room temperature, a mixture of H 2 and O 2 will not produce H 2 O . However, if the mixture is sparked, water is produced with explosive violence, thereby proving the prediction thermodynamics makes concerning this reaction. One limitation of thermodynamics is that it does not give any indication of how fast the reaction will proceed, i.e., in essence, the laws of thermodynamics do not contain time as a variable. Thus thermodynamics is only interested in where the system was initially and where it is after the completion of the process. It does not care how the attainment of the final condition came about or how long it takes to reach this condition. In the case of a chemical reaction, for example, thermodynamics may tell us that the reaction will go spontaneously, but it cannot tell us how long the reaction will take to reach equilibrium or what the path of the reaction will be. The latter two problems are dealt with in the study of chemical kinetics. 5.2 DEFINITION OF THERMODYNAMIC TERMS Before developing the laws of thermodynamics, consideration will be given to the definition of the terms commonly used in this field, since a clear understanding of these definition and terms will aid immensely in the discussions to follow. ENERGY Energy is usually defined as the capacity to do work. Kinetic energy, potential energy, chemical energy, and thermal energy are forms of energy particularly useful to the chemist. Kinetic energy is defined as the energy produced by a moving object. For an object of mass m moving at a velocity v , the kinetic energy is equal to mv 2 ....
View Full Document