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:
“Prepare for death, if here at night you roam,
And sign your will before you sup from home.”
—Samuel Johnson (1709–1784)
“No good poetry is ever written in a manner twenty years old, for to write in such a manner shows conclusively that the writer thinks from books, convention and cliché, not from real life.”
—Ezra Pound (1885–1972)
“A man’s got to work for more than himself and his kids to feel right.”
—John Dos Passos (1896–1970)