11.5.1 Thermodynamic Processes

There are four kinds of thermodynamics processes that occur frequently in practical situations, namely:

Isobaric:          constant pressure       (\displaystyle {{W}_{{ON}}}=-p\Delta V )

Isochoric:        constant volume          (\displaystyle {{W}_{{ON}}}=0 )

Isothermal:      constant temperature  (\displaystyle \Delta U=0 )

Adiabatic:        zero heat transfer       (\displaystyle Q=0 )

The tables below summarize the signs of the terms in the first law for the different processes.

ProcessΔUQWON
isobaricexpansion+[1]+
 compression[2]+
isochoriccooling0
 heating++0
isothermalexpansion0+
 compression0+
adiabaticexpansion0
 compression+0+

Let’s look at each of them in detail in the following sections.


[1]The internal energy must increase since p is constant and V has increased, and \displaystyle pV=nRT .

[2] same logic as that for isobaric expansion.

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