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 only sign over everything,
the house, the dog, the ladders, the jewels,
the soul, the family tree, the mailbox.
Then I can sleep.
Maybe.”
—Anne Sexton (1928–1974)
“Mankind owes to the child the best it has to give.”
—United Nations Convention on the Rights of the Child, 1989.
“We might remind ourselves that criticism is as inevitable as breathing, and that we should be none the worse for articulating what passes in our minds when we read a book and feel an emotion about it, for criticizing our own minds in their work of criticism.”
—T.S. (Thomas Stearns)