The laws of thermodynamics describe the behavior of energy in different systems.  The first law states that energy cannot be created or destroyed, only converted from one form to another.  The second law states that the total entropy (a measure of the degree of disorder in a system) in a closed system will always increase over time, and that energy will always tend to flow from hotter to cooler objects.  The third law states that it is impossible to reach absolute zero (the lowest possible temperature).

System Types

Boundary  -  The real or imaginary surface that separates the system ftom the surroundings and can be fixed or movable.
Closed System  -  Exchanges only energy with its surroundings.  No mass can cross the system.
Isolated System  -  Keeps the energy and matter within the system and everything else out.  No transfer in or out.
Open System  -  Freely exchanges energy and matter with its surroundings.  Both mass and energy can cross the boundary.

Properties of a System

The identifiable and observable characteristics of a system by which it can be specified.

Extensive Properties  -  Those properties which depend on the size of the system.  These properties are directly related to the mass.

• Enthalpy
• Entropy
• Gibbs Free Energy
• Heat Capacity
• Internal Energy
• Mass
• Volume
• etc.

Intensive Properties  -  Those properties of the system which do not depend on the size of the system.  These properties are not related to the mass.

• Color
• Density
• Pressure
• Temperature
• Thermal Expansion
• Velocity
• Viscosity
• etc.

Thermodynamic Processes

Any process that involves heat energy moving within a system or between systems.

Adiabatic Process  -  No heat is transferred to or from the system.
Cyclic Process  -  The system at the end is the same as the state at the beginning.  The system does not change over a complete cycle.
Irreversible Process  -  Cannot return both the system and the surroundings to their original conditions.
Isenthalpic Process  -  A process of constant enthalpy.
Isochoric Process  -  The system’s volume does not change.
Isobaric Process  -  The system’s pressure does not change.
Isothermal Process  -  The system’s temperature remains constant.
Non-quasi-static Process  -  Most of the processes happening around us can be termed non-quasi-static process.
Quasi-static Process  -  Slow enough for the system to maintain internal thermodynamic equilibrium.
Reversible Process  -  Can be made to retrace its path by differential changes in the environment.  It leaves no change in either the system or surroundings.