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

Isobaric: constant pressure ( )

Isochoric: constant volume ( )

Isothermal: constant temperature ( )

Adiabatic: zero heat transfer ( )

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

Process | ΔU | Q | W_{ON} | |

isobaric | expansion | +[1] | + | − |

compression | −[2] | − | + | |

isochoric | cooling | − | − | 0 |

heating | + | + | 0 | |

isothermal | expansion | 0 | + | − |

compression | 0 | − | + | |

adiabatic | expansion | − | 0 | − |

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 .

[2] same logic as that for isobaric expansion.