Summarizing the First Law of Thermodynamics and Some Simple Processes

Summary

• One of the important implications of the first law of thermodynamics is that machines can be harnessed to do work that humans previously did by hand or by external energy supplies such as running water or the heat of the Sun. A machine that uses heat transfer to do work is known as a heat engine.
• There are several simple processes, used by heat engines, that flow from the first law of thermodynamics. Among them are the isobaric, isochoric, isothermal and adiabatic processes.
• These processes differ from one another based on how they affect pressure, volume, temperature, and heat transfer.
• If the work done is performed on the outside environment, work (\(W\)) will be a positive value. If the work done is done to the heat engine system, work (\(W\)) will be a negative value.
• Some thermodynamic processes, including isothermal and adiabatic processes, are reversible in theory; that is, both the thermodynamic system and the environment can be returned to their initial states. However, because of loss of energy owing to the second law of thermodynamics, complete reversibility does not work in practice.

Glossary

heat engine

a machine that uses heat transfer to do work

isobaric process

constant-pressure process in which a gas does work

isochoric process

a constant-volume process

isothermal process

a constant-temperature process

adiabatic process

a process in which no heat transfer takes place

reversible process

a process in which both the heat engine system and the external environment theoretically can be returned to their original state