Thermodynamics is a fundamental chapter of physical chemistry that deals with energy, heat, work, and the laws governing their interconversion during physical and chemical processes. It provides a macroscopic description of nature by focusing on systems as a whole rather than on individual molecules.
Every natural phenomenon, such as the melting of ice, expansion of gases, flow of heat,combustion of fuels, and chemical reactions, obeys the principles of thermodynamics.
These principles enable us to predict whether a process is feasible, how much energy is involved, and the conditions under which equilibrium is established.
Thermodynamics does not explain the rate or mechanism of a process. Instead, it answers fundamental questions related to energy balance and direction of change. For this reason, it forms the theoretical backbone of chemistry, physics, engineering, and
biological sciences.
Scope and Importance of Thermodynamics
The scope of thermodynamics extends from simple laboratory reactions to complex industrial and biological systems. In chemistry, it helps in understanding reaction energetics, phase stability, chemical equilibrium, and electrochemical processes.
The universal nature of thermodynamic laws makes them independent of the physical state or chemical composition of matter. Once the basic concepts are mastered, the same laws can be applied to gases, liquids, solids, and mixtures alike.
Basic Terminology in Thermodynamics
System, Surroundings, and Universe
A system is the part of the universe selected for thermodynamic study.
Everything outside the system that can interact with it is known as the surroundings. The system and surroundings together constitute the universe.
The boundary separating the system from its surroundings may be real or imaginary, fixed or movable. All thermodynamic interactions are analyzed in terms of energy transfer across this boundary.
Types of Thermodynamic Systems
Based on the exchange of matter and energy with the surroundings, thermodynamic systems are classified as open, closed, and isolated systems. An open system exchanges both matter and energy, a closed system exchanges only energy, and an isolated system exchanges neither matter nor energy.
State of a System and Thermodynamic Variables
The state of a thermodynamic system is defined by measurable properties such as pressure, volume, temperature, and composition. These properties are called thermodynamic variables. When these variables have definite values, the system is said to be in a well-defined state.
Thermodynamic variables are further classified as intensive or extensive properties.
Intensive properties are independent of the amount of matter present, whereas extensive properties depend on the size of the system.
State Functions and Path Functions
Quantities that depend only on the state of the system and not on the path of the process are called state functions, such as internal energy and enthalpy. Quantities like heat and work depend on the path of the process and are therefore known as path functions.
This distinction forms the conceptual basis for the laws of thermodynamics discussed later in this chapter.