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:
“When two people decide to get a divorce, it isn’t a sign that they “don’t understand” one another, but a sign that they have, at last, begun to.”
—Helen Rowland (1875–1950)
“Every one knows about the young man who falls in love with the chorus-girl because she can kick his hat off, and his sister’s friends can’t or won’t. But the youth who marries her, expecting that all her departures from convention will be as agile or as delightful to him as that, is still the classic example of folly.”
—Katharine Fullerton Gerould (1879–1944)
“So is the English Parliament provincial. Mere country bumpkins, they betray themselves, when any more important question arises for them to settle, the Irish question, for instance,—the English question why did I not say? Their natures are subdued to what they work in. Their “good breeding” respects only secondary objects.”
—Henry David Thoreau (1817–1862)