系统、周围环境和墙壁

Thermodynamics deals with the science of “motion” (dynamics) and/or the transformation of “heat” (thermo) and energy into various other energy– containing forms. The flow of energy is of great importance to engineers involved in the design of the power generation and process industries. Thermodynamics provides an understanding of the nature and degree of energy transformations, so that these can be understood and suitably utilized.

Thermodynamics comprises both a macroscopic and microscopic part.

The macroscopic part is what is usually learnt first and covers macroscopic properties such as temperature.

What then is the microscopic part about? We know that at its most fundamental level, things are comprised of many atoms and molecules that move. However, because it is impossible to accurately determine the exact equation of motion of each atom / molecule because of randomness, we need to turn to the statistical mechanics instead and use statistics and probabilities, which is what microscopic thermodynamics comprises.

A system that is thermally insulated from its surroundings can be looked at as a system where there are no heat exchanges between it and its surroundings. For example, we define a system to a box. If there is no heat exchange between this box and its surroundings, then it can be said to be thermally insulated from its surroundings.

A system describes basically a transmission of energy, and the total energy in the of system is enthalpy (internal energy + (pressure*volume) = enthalpy). The surroundings can affect enthalpy, and walls prevent changes in the system.