Introduction to the First Law and Foundations of Thermodynamics

Overview and Definition of Thermodynamics

  • Etymology and Scope: The word 'thermodynamics' implies the flow of heat. However, the subject is much more comprehensive in its application and scope.
  • Core Subject Matter: It deals with energy changes accompanying all types of physical and chemical processes.
  • Foundational Generalizations: Thermodynamics is established upon two generalizations known as the First and the Second law of thermodynamics.
  • Basis of the Laws: These laws are based on human experience rather than formal mathematical proofs.
  • Bulk Matter Focus: The laws hold true because nothing contrary to them has ever been observed in the behavior of matter in bulk. Specifically, scientists believe that nothing contrary to these laws will ever be discovered.
  • Independence from Structure: The laws of thermodynamics are entirely independent of the atomic or molecular structure of matter.

Importance of Thermodynamics in Physical Chemistry

  • Fundamental Status: Thermodynamics is a fundamental subject of great importance within the field of physical chemistry.
  • Deduction of Physical Laws: Most major generalizations in physical chemistry can be deduced from the laws of thermodynamics, including:
    • The van't Hoff law of dilute solutions.
    • Raoult's law of vapour pressure lowering.
    • The distribution law.
    • The law of chemical equilibrium.
    • The phase rule.
    • The laws of thermochemistry.
  • Predicting Feasibility (Spontaneity): The subject helps lay down the criteria for predicting whether a process, including a chemical reaction, is feasible or spontaneous under a given set of conditions. These conditions typically include:
    • Temperature (TT).
    • Pressure (PP).
    • Concentration.
  • Determining Extent of Processes: Thermodynamics allows scientists to determine the extent to which a process (or reaction) can proceed before it reaches the state of equilibrium.

Limitations of Thermodynamics

  • Macroscopic Application vs. Microscopic Units: The laws of thermodynamics apply only to matter in bulk and not to individual atoms or molecules. They describe the behavior of assemblages of a vast number of molecules.
  • Absence of Kinetic Information: While thermodynamics can predict whether a process is feasible under a certain set of conditions, it provides no information regarding the rate at which the process proceeds.
  • Case Study (Hydrogen and Oxygen): Thermodynamics predicts that hydrogen and oxygen gases should react at ordinary temperatures to yield liquid water.
    • The reaction is: 2H2(g)+O2(g)→2H2O(l)2H_2(g) + O_2(g) \rightarrow 2H_2O(l).
    • Despite this prediction, thermodynamics does not specify if the reaction is fast or slow.
    • Experimental evidence shows that in the absence of a catalyst, this particular reaction is extremely slow.

Fundamental Thermodynamic Terminology

  • System: A system is defined as any specified portion of matter under study which is separated from the rest of the universe with a bounding surface. A system may consist of one or more substances.
  • Surroundings: The surroundings comprise the rest of the universe which might be in a position to exchange energy and matter with the system.
    • Common Examples: In simple cases, the surroundings generally imply the air or a water-bath in which the system under examination is immersed.
  • Isolated System: An isolated system is defined as a system which can exchange neither energy nor matter with its surroundings.