Sign Convention For Work
The motivation for the specific sign conventions of thermodynamics comes from early development of heat engines. When designing a heat engine, the goal is to have the system produce and deliver work output. The source of energy in a heat engine, is a heat input.
If the volume compresses (delta V = final volume - initial volume < 0), then W < 0. That is, during isobaric compression the gas does negative work, or the environment does positive work. Restated, the environment does positive work on the gas.
If the volume expands (delta V = final volume - initial volume > 0), then W > 0. That is, during isobaric expansion the gas does positive work, or equivalently, the environment does negative work. Restated, the gas does positive work on the environment.
If heat is added to the system, then Q > 0. That is, during isobaric expansion/heating, positive heat is added to the gas, or equivalently, the environment receives negative heat. Restated, the gas receives positive heat from the environment.
If the system rejects heat, then Q < 0. That is, during isobaric compression/cooling, negative heat is added to the gas, or equivalently, the environment receives positive heat. Restated, the environment receives positive heat from the gas.
Read more about this topic: Isobaric Process
Famous quotes containing the words sign, convention and/or work:
“I can express no kinder sign of love
Than this kind kiss.”
—William Shakespeare (1564–1616)
“By convention there is color, by convention sweetness, by
convention bitterness, but in reality there are atoms and space.”
—Democritus (c. 460–400 B.C.)
“Even if matter could do every outward thing that God does, the idea of it would not work as satisfactorily, because the chief call for a God on modern men’s part is for a being who will inwardly recognize them and judge them sympathetically. Matter disappoints this craving of our ego, so God remains for most men the truer hypothesis, and indeed remains so for definite pragmatic reasons.”
—William James (1842–1910)