Thermodynamics Unit I: Basic Concepts

Thermodynamics Introduction

• Thermodynamics is the science of energy and its transformation, and its effects on physical properties of substances.
• Deals with equilibrium and feasibility of a process.
• Involves the relationship between heat and work and properties of systems in equilibrium.

Thermodynamic System

• Defined as a quantity of matter or a region in space chosen for study.
• The mass and region outside the system is called the surrounding.
• The boundary that separates the system from the surrounding can be real or imaginary.

Types of Systems

• Closed System (Control Mass):
  • Consists of a fixed amount of mass.
  • No mass can cross its boundary or leave/enter.
  • Energy in the form of heat or work can cross the boundary.
  • Volume does not have to be fixed.
  • Example: piston-cylinder device.
• Open System (Control Volume):
  • A properly selected region in space.
  • Both mass and energy can cross the boundary.
  • Boundary is called a control surface and can be real or imaginary.
  • Example: compressor, turbine, nozzle.

Approaches to Thermodynamic Study

• Macroscopic Approach:
  • Considers a certain quantity of matter without considering molecular-level events.
  • Requires simple mathematical formulae.
  • Used in classical thermodynamics.
  • Concerned with overall behavior of the system.
  • Few properties are required to describe the system.
• Microscopic Approach:
  • Considers matter to be comprised of many tiny particles (molecules) that move randomly.
  • Effects of molecular motion are considered.
  • Requires advanced statistical and mathematical methods.
  • Used in statistical thermodynamics.
  • Requires knowledge of the structure of matter.

Properties of a System

• Property: Any characteristic of a system.
• Intensive Properties:
  • Independent of the size of the system.
  • Examples: temperature, pressure, density.
  • Not additive.
  • Value remains the same whether considering the whole system or a part of it.
• Extensive Properties:
  • Dependent on the size or extent of the system.
  • Examples: mass, volume, total energy.
  • Additive.
  • Value for an overall system is the sum of its values for the parts into which the system is divided.

Specific Properties

• Specific Properties: Extensive properties per unit mass.
• Specific Volume: The volume of a substance per unit mass.
• Specific Energy: Energy per unit mass.
• Specific Gravity (or Relative Density): Density of a substance with respect to a standard substance at a specified temperature.

Continuum and State

• Continuum: A continuous, homogeneous matter with no holes.
• State: The condition of a system at any instant of time, described by its properties.
• Equilibrium: A state of balance where there are no unbalanced potentials within the system.

Processes and Path Functions

• Process: A change that a system undergoes from one equilibrium state to another.
• Path Function: A quantity whose value depends on the path followed during a change of state.
• Point Function: A quantity whose change is independent of the path.
• Quasi-Equilibrium Process: A process that proceeds in such a way that the system remains infinitesimally close to an equilibrium state at all times.

Temperature and Pressure

• Temperature: A measure of hotness or coldness.
• Pressure: Force exerted by a fluid per unit area.
• Pressure Scales: Related to absolute temperature scales.
• Kelvin Scale: Related to Celsius scale by T(K) = T(C) + 273.16.
• Rankine Scale: Related to Fahrenheit scale by T(R) = T(F) + 459.67.

Thermodynamic Equilibrium

• Thermodynamic Equilibrium: A state where no changes in macroscopic properties are observed if the system is isolated from its surroundings.
• Conditions for Equilibrium:
  • Thermal equilibrium (equality of temperature).
  • Mechanical equilibrium (equality of pressure).
  • Chemical equilibrium (equality of chemical potential).

Reversible and Irreversible Processes

• Reversible Process: A process that can be executed in either direction without producing any changes in the rest of the universe.
• Irreversible Process: A process that cannot be restored to its initial state without producing changes in the rest of the universe.

Work and Heat Transfer

• Thermodynamic Work: Energy transfer that occurs when a system undergoes a change in volume or pressure.
• Pressure-Volume Work (PV Work): Work done by or on a system at constant pressure.
• Sign Convention: Work done by the system is positive, and work done on the system is negative.

Introduction to thermodynamics, a science dealing with energy transformation and its effects on physical properties of substances. Covers equilibrium, feasibility, and relationships between heat, work, and system properties.