The Second Law of Thermodynamics

Carnot cycle

cycle that consists of two isotherms at the temperatures of two reservoirs and two adiabatic processes connecting the isotherms

Carnot engine

Carnot heat engine, refrigerator, or heat pump that operates on a Carnot cycle

Carnot principle

principle governing the efficiency or performance of a heat device operating on a Carnot cycle: any reversible heat device working between two reservoirs must have the same efficiency or performance coefficient, greater than that of an irreversible heat device operating between the same two reservoirs

Clausius statement of the second law of thermodynamics

heat never flows spontaneously from a colder object to a hotter object

coefficient of performance

measure of effectiveness of a refrigerator or heat pump

cold reservoir

sink of heat used by a heat engine

disorder

measure of order in a system; the greater the disorder is, the higher the entropy

efficiency (e)

output work from the engine over the input heat to the engine from the hot reservoir

entropy

state function of the system that changes when heat is transferred between the system and the environment

entropy statement of the second law of thermodynamics

entropy of a closed system or the entire universe never decreases

heat engine

device that converts heat into work

heat pump

device that delivers heat to a hot reservoir

hot reservoir

source of heat used by a heat engine irreversibility phenomenon associated with a natural process

irreversible process

process in which neither the system nor its environment can be restored to their original states at the same time

isentropic

reversible adiabatic process where the process is frictionless and no heat is transferred

Kelvin statement of the second law of thermodynamics

it is impossible to convert the heat from a single source into work without any other effect

perfect engine

engine that can convert heat into work with 100% efficiency

perfect refrigerator (heat pump)

refrigerator (heat pump) that can remove (dump) heat without any input of work

refrigerator

device that removes heat from a cold reservoir

reversible process

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

third law of thermodynamics

absolute zero temperature cannot be reached through any finite number of cooling steps