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:
“The radio ... goes on early in the morning and is listened to at all hours of the day, until nine, ten and often eleven oclock in the evening. This is certainly a sign that the grown-ups have infinite patience, but it also means that the power of absorption of their brains is pretty limited, with exceptions, of courseI dont want to hurt anyones feelings. One or two news bulletins would be ample per day! But the old geese, wellIve said my piece!”
—Anne Frank (19291945)
“Mankind owes to the child the best it has to give.”
—United Nations Convention on the Rights of the Child, 1989.
“... in love, barriers cannot be destroyed from the outside by the one to whom the cause despair, no matter what he does; and it is only when he is no longer concerned with them that, suddenly, as a result of work coming from elsewhere, accomplished within the one who did not love him, these barriers, formerly attacked without success, fall futilely.”
—Marcel Proust (18711922)