# Thermodynamics

Thermodynamics is the study of heat. Thermodynamics produces a wide range of applications such as steam engines and heat pumps. "Thermodynamics" comes from the Greek words "therme" which means heat and "dynamikos" which means force, or power. So, "Thermodynamics" is essentially the study of forces due to heat or heat due to forces. It deals with the conversion of energies through various forms and to various systems, as well as energies' relationships with the properties of a system.

Within the engineering sciences, Thermal Engineering deals with the applications of thermodynamics to work producing and work absorbing devices, often to understand and improve their performance.

## Terminology

An understanding of the common terminology would be very useful before going further.

System: The region of interest for the purpose study. It is assumed that this region can be considered separated or weakly-interacting with the rest of the Universe.

Boundary: An imaginary line that encompasses the region of interest. It should be noted that boundary effects are neglected in Thermodynamics. This can be justified by comparing the number of molecules in a volume of condensed matter to the number of molecules near the surface.

Equilibrium: The state where heat flow into and out of the system are equal. In the case of static equilibrium, no change in temperature occurs. During dynamic equilibrium, more heat flows into the system at certain times, and out at others, so that the temperature does change, but, on average, still stays the same.

Microscopic and Macroscopic Descriptions: The state of a system can be specified in two key ways. The first is with a microscopic description, where the position and momentum of every particle is specified. The other is a macroscopic description, where a relatively few thermodynamic variables (i.e. temperature, pressure, volume) are specified.

Heat: Energy transfer due to temperature difference.

Work: Energy transfer due to movement.

Temperature: Temperature is a property which measures the degree of hotness or coldness of body. This is due to molecular vibration.

## Principal laws of Thermodynamics

• Zeroeth law of thermodynamics states that if two objects are each in thermal equilibrium with a third, then they are also in thermal equilibrium with each other.
• The first law of thermodynamics states that energy can be neither created nor destroyed.
• The second law of thermodynamics states that dQ=TdS. Here dQ is the change of heat,T is the temperature in Kelvin and dS is the entropic change.
• The third law of thermodynamics states that at absolute zero (the lowest possible temperature), there is no molecular movement.

## Introduction to Thermodynamics

Now let's see the chapters we will cover in what can be called an "Introduction to Thermodynamics" as a University course. Here we are: