Fundamentals of Thermodynamics

Working note — Part of my personal research notebook. Entries may be incomplete and are revised over time.

• physical system: refers to a specific portion of the universe that we are interested in studying, separated from its surrounding by a boundary, which can be real or imaginary.
  • everything outside the system is called the surroundings/environment
  • e.g., gas enclosed in a cylinder with a piston: gas is the system, inner surface of the cylinder and the piston form the boundary, and everything else is the surroundings
• state of the physical system: its condition at a specific point in time, defined by a set of measurable properties called state variables.
  • variables typically include: pressure (P), volume (V), temperature (T), number of particles (n)
  • a change from one state to another is called a process
  • e.g., a gas in a cylinder’s state could be defined by a presssure of 1 bar, volume of 1 liters, and a temperature of 300 Kelvin.
    • you push the piston down, it changes the volume, and the T,P migh change, leading to a new state
• physical law of thermodynamics: the fundamental principle that describes the relationships and interactions between the properties of the system
  • these laws are based on empirical observations and are considered applicable under their specified conditions
    • e.g., first law of thermodynamics: conservation of energy
      • applicable only to any closed system, where energy can be exchanged as heat and work, but matter cannot cross the boundary
    • method of application: $\Delta U = Q - W$, where $\Delta$ is the change of the internal energy of the system, $Q$ is the heat added to the system, and $W$ is the work done by the system.