Thermodynamics

A System is a quantity of matter or a collection of objects that is enclosed by boundaries either real or imaginary.  Everything beyond our boundaries is called the Surroundings.

A Thermally Insulated System is one where no heat can flow between the system and its surroundings.

Adiabatic Walls are perfectly insulated walls that do not let heat flow between the system and its surroundings.

Diathermal Walls permit heat to flow between the system and its surroundings.

A Heat Reservoir is a system that will not change temperature no matter how much heat enters or leaves it.  Of course there is no such thing as a perfect heat reservoir, but a swimming pool could be considered to be a heat reservoir.  If you add an ice cube to your swimming pool there is no noticeable lowering of the pools temperature.

 The State of a System can be defined as the particular temperature, pressure and volume of a system.

A Process is a change in the State of the System.  When a system undergoes a process the temperature, pressure and volume that describe the state of the system will change.  Processes are either Reversible or Irreversible.

An Irreversible Process is a process for which the intermediate steps between the original state and the final state are not known.  This does not mean that it is impossible to return the system to its original state.  Rather it means that it is impossible to return the original state by retracing the path that was taken to go from the original state to the final state.

A Reversible Process is a process for which the intermediate steps between the original state and the final state are known.  The process path is known so it is possible to return to the original state by way of the path that was taken to go from the original state to the final state.

Zeroth Law of Thermodynamics → Two systems individually in thermal equilibrium with a third system are in thermal equilibrium with each other.

For example, if a book is in thermal equilibrium with room 306, and the book is in thermal equilibrium with room 308, then room 306 is in thermal equilibrium with room 308.

First Law of Thermodynamics → A change in the Internal Energy of system is equal to heat and work that enters or leaves the system.

Using the Conservation of Energy principle we have said that a change in Internal Energy is equal to Work.  And we have said that a change in Internal Energy is equal to Heat.  So...

Δ Energy_Internal  =   Heat + Work

Δ E_Internal  =  Q + W

Δ U  =  Q + W

+ Q  →  Heat is added to the system.

- Q  →  Heat is removed from the system.

+ W  →  Work is added to the system or Work is done on the system.

- W  →  Work is removed from the system or Work is done by the system.

Isobaric Process → A constant pressure process. 

Isometric Process or Isochoric Process → A constant volume process. 

Isothermal Process → A constant temperature process. 

Adiabatic Process → A process where there is no heat transfer.

Second Law of Thermodynamics → Heat flow spontaneously form a substance at a higher temperature to a substance at a lower temperature and does not flow spontaneously in the reverse direction.

jj