Summarizing the First Law of Thermodynamics

Summary

• The first law of thermodynamics is given as \(\Delta U=Q-W\), where \(\Delta U\) is the change in internal energy of a system, \(Q\) is the net heat transfer (the sum of all heat transfer into and out of the system), and \(W\) is the net work done (the sum of all work done on or by the system).
• Both \(Q\) and \(W\) are energy in transit; only \(\Delta U\) represents an independent quantity capable of being stored.
• The internal energy \(U\) of a system depends only on the state of the system and not how it reached that state.
• Metabolism of living organisms, and photosynthesis of plants, are specialized types of heat transfer, doing work, and internal energy of systems.

Glossary

first law of thermodynamics

states that the change in internal energy of a system equals the net heat transfer into the system minus the net work done by the system

internal energy

the sum of the kinetic and potential energies of a system’s atoms and molecules

human metabolism

conversion of food into heat transfer, work, and stored fat