Glossary

adiabatic process

a process in which no heat transfer takes place

Carnot cycle

a cyclical process that uses only reversible processes, the adiabatic and isothermal processes

Carnot efficiency

the maximum theoretical efficiency for a heat engine

Carnot engine

a heat engine that uses a Carnot cycle

change in entropy

the ratio of heat transfer to temperature $Q/T$

coefficient of performance

for a heat pump, it is the ratio of heat transfer at the output (the hot reservoir) to the work supplied; for a refrigerator or air conditioner, it is the ratio of heat transfer from the cold reservoir to the work supplied

cyclical process

a process in which the path returns to its original state at the end of every cycle

entropy

a measurement of a system's disorder and its inability to do work in a system

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

heat engine

a machine that uses heat transfer to do work

heat pump

a machine that generates heat transfer from cold to hot

human metabolism

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

internal energy

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

irreversible process

any process that depends on path direction

isobaric process

constant-pressure process in which a gas does work

isochoric process

a constant-volume process

isothermal process

a constant-temperature process

macrostate

an overall property of a system

microstate

each sequence within a larger macrostate

Otto cycle

a thermodynamic cycle, consisting of a pair of adiabatic processes and a pair of isochoric processes, that converts heat into work, e.g., the four-stroke engine cycle of intake, compression, ignition, and exhaust

reversible process

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

second law of thermodynamics

heat transfer flows from a hotter to a cooler object, never the reverse, and some heat energy in any process is lost to available work in a cyclical process

second law of thermodynamics stated in terms of entropy

the total entropy of a system either increases or remains constant; it never decreases

statistical analysis

using statistics to examine data, such as counting microstates and macrostates