Definitions Flashcards
Engine
A machine designed to convert one or more forms of energy into mechanical energy
Heat engine
A physical or theoretical device that converts thermal energy to mechanical output
Carnot heat engine
A hypothetical engine that operates on the reversible Carnot Cycle
The system
The part whose properties we are studying
Surroundings
Involve everything else outside or around the system
Boundary
What the system exchanges matter or energy across to interact with its surroudings
Isolated System
Neither matter nor energy can be exchanged
Closed system
Only energy can be exchanged
Open system
Both energy and matter can be exchanged
Diathermal
When a system may be influenced thermally
Conditions for thermodynamic equilibrium
-Mechanical equilibrium (constant pressure)
-Chemical equilibrium (constant particle concentration)
-Thermal equilibrium (constant temperature)
Extensive vs intensive
A state variable that depends on the physical size of the system vs one that is independent of the system’s size
Conditions for reversibility
-process can be reversed by an infinitesimal change in conditions
-quasistatic
-no hysteresis
Quasisatic
Carried out so slowly that every state the system passes through may be considered an equilibrium state
Hysteresis
When a process is reversed it does not retrace its previous path but follows a different one
Irreversible
When energy is permanently lost from the system due to dissipative forces such as friction
Common reversible processes
Isothermal, isochoric, isobaric, adiabatic
Isothermal
The temperature of the system remains constant
Isochoric
The volume of the system remains constant
Isobaric
The pressure of the system remains constant
Adiabatic (adiathermal)
No heat is exchanged between the system and its surroundings
Thermal equilibrium
When there is no net heat flow between bodies after they have been in thermal contact with each other through a diathermal wall. They will have restricted value of their pressure/volume coordinate systems.
The zeroth law
If two systems are separately in thermal equilibrium with a third, then they must also be in thermal equilibrium with each other
Work is positive when
Work is done on the system of interest
Work is negative when
The system does work on the surroundings
Work
Energy transferred between a system and its surroundings when a force is applied over a distance or when the system undergoes a change in its external variables
Heat
An energy transfer that happens between a system and its surroundings due to temperature difference
First law
Energy is conserved and heat and work are both forms of energy. dU = dQ + dW
A small change of entropy of a system, dS , is defined as
The small change in heat flow per unit temperature into the system, provided the heat flow corresponds to a reversible process
Carnot cycle four steps
Isothermal expansion, adiabatic expansion, isothermal compression, adiabatic compression
Kelvin statement
No process is possible whose sole result is the complete conversion of heat into work
Clausius statement
No process is possible whose sole result is the transfer of heat from a colder to a hotter body
Second law
No process is possible where the total entropy of the universe decreases. The total change in entropy is always greater than or equal to zero
Carnots theorem
No engine operating between two given reservoirs can be more efficient than a carnot engine operating between the same two reservoirs
Isentropic process
A process that is both adiabatic and reversible
The second law- another version
The entropy of an isolated system tends to a maximum. As the universe of a whole is an isolated system, internal energy of universe is constant and entropy of universe can only increase, we are heading towards the heat death of the universe
