Thermodynamics Introduction

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.

Learn the basics of thermodynamics, the science of energy and its transformation, and its effects on physical properties of substances.