Thermo 1 Definitions Flashcards
Thermodynamics
The science fo the relationship between heat and mechanical work
Closed System
A system in which no mass crosses the system boundary
State postulate
In a simple equilibrium, a system can be described by just two properties, thereby fixing the other four.
Simple system
Only one chemical component, existing in one physical state
Gauge pressure
Pressure above atmospheric pressure
Absolute pressure
Pressure measured using zero as a datum
Zeroth Law
If A is in equilibrium with both B and C, it follows that both B and C are in equilibrium
Process
Transforms a system from one equilibrium to another
Quasi-equilibrium process
A process that is very close to equilibrium along a path
Stationary system
A system where changes in KE or PE are small
Internal Energy
The combination of all microscopic forms of energy in a fluid
Cycle
A closed system undergoes a cycle when it passes through a series of events which leaves its final state equal to all aspects of its initial state
Property
Characteristics used to describe an object and is independent of path - temperature, pressure, volume, enthalpy, entropy, internal energy, density
Pressure
Force per unit area exerted on a boundary
Two-point temperature scale
A scale using two reference temperatures - eg celcius
Thermodynamic temperature scale
No dependence on the behaviour of a substance - eg kelvin
Path
How the system is transformed during a process
Work
The product of a force and the distance over which the force is applied
First Law
When a closed system is taken through a cycle, the work delivered to the surroundings is equal to the net heat taken from the surroundings
Axiom
A statement that cannot be proved, but no cases exist to disprove it.
First Law - corollary 1
There exists a property of a closed system such that a change in its value is equal to the difference between the heat supplied and the work done during any change of state
First Law - corollary 2
The internal energy of a closed system remains unchanged if the system is isolated from its surroundings
First Law - corollary 3
A perpetual motion machine of the first kind is impossible - one which produces work without the supply of heat.
Equilibrium
All driving forces on a system are balanced
Intensive properties
Properties which have no dependence on the size of a system (temperature, specific volume, density, pressure, etc)
Extensive properties
Properties that depend on the size of a system (V, m, etc)
Non-Flow Energy Equation
ΔU=Q+W. Derived from the 1st corollary of the first law.
Specific heat capacity
The quantity of energy required to raise the temperature of a unit mass by one degree at constant volume/pressure.
Enthalpy
A combination property, comprising internal energy and flow work. H = U+pV
Isolated system
A system where no mass, heat or work crosses the system boundary
Isochoric
Constant volume process
Isobaric
Constant pressure process
Isothermal
Constant temperature process
Isentropic
Constant entropy process - no heat transfer from surroundings
Isentropic relationship
pV^γ = constant
Polytropic process
pV^n = constant
Steady flow process
A process with a continuous flow of mass
Kelvin-Planck Statement of the Second Law
It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce an amount of work.
Clausius Statement of the Second Law
It is impossible to construct a device that operates in a cycle and transfers heat from a cooler to a hotter body without work being done on the system by the surroundings.
Reservoir
A very large heat store whose temperature changes only infinitesimally when heat is added or rejected
Source
Hot reservoir
Sink
Cold reservoir
Perpetual motion machine of the second kind
A cyclic engine connected to one reservoir only and producing work
Corollary 1 of the Second Law
It is impossible to construct a device that operates in a cycle and transfers heat from a cooler to a hotter body without work being done on the system by the surroundings. (Clausius statement)
Reversible
A process in which both fluid and surroundings can be restored to their original states
Isentropic efficiency
The ratio of real-world work to reversible work
Corollary 2 of the Second Law
It is impossible to construct an engine operating between only two reservoirs which will have a higher efficiency than a reversible engine operating between the same two reservoirs
Corollary 3 of the Second Law
All reversible engines operating between the same two reservoirs have the same efficiency
Clausius Inequality (Corollary 6)
cyclic int(dQ/T) <= 0
Adiabatic
No heat transfer across the system boundary
Closed cycle
Working gas is recirculated around the engine
Open cycle
Gas enters and leaves the engine
Compression ratio
r = Vmax/Vmin
