Definitions and E Balance Flashcards
A ____ system has no mass exchange
Closed
A open system that has mass exchanged is studied by looking at a…
Control Volume
Are boundaries fixed?
No, they may move or change shape/size over time
A ___ system has no mass exchange and no ____
Isolated, energy
A process is a transformation from one state…
to another state
A property is a __________ of a system that desciribes its ____
macroscopic characteristic, condition
An intensive property is
size INDEPENDENT
an Extensive property is
size DEPENDENT
_____ is a condition of a system at a given time described by it’s properties
STATE
A State is called “fixed” if….
a minimum number of properties known to describe it completely
Energy is a ____ property
extensive
Some examples of intensive properties
Temperature, Pressure, density, molar mass
True or false: there may be infinitely many process paths between any 2 given states
TRUE
at ___ state, the system condition does not change with time
steady
_____ is the lowest energy state possible, where the system usually is at ____
DEAD STATE, equilibrium with its surroundings
An equilibrium is ….
the balance of an influence (ex mechanical, chemical, phase)
Thermodynamic Equilibrium means….
all influences on a system are in balance at the same time
Quasi-equilibrium state means…
system is very close to equilibrium, it’s a very slow process, completed in a piece wise equilibrium
____ is energy in transit
Work
Equation for work (mechanical)
W = integral{Ft * ds}
2nd law
entropy naturally increases; restoring order requires effort
Work is = 0 if there is no ____ in the direction of the force applied at the boundary
displacement
Power = F_vector *…
(dot product) w/ velocity vector
Work is _____ energy transit
path dependent
Change in stored system energy is ____
path independent
Equation for Work done by a gas through volume expansion under pressure
W = integral{p * dv}
Equation for Work (electric)
Integral { V(t)I(t)dt}
Work_dot (electric) = Power =
I*V
0th law
When two objects at different temperatures, energy flows from warmer to colder in the form of heat until they reach thermal equilibrium (same temperature)
Work is ____ valuable form of energy transfer than heat
More
These 2 types of heat interaction rely on physical contact
convection and conduction
____ is the dominant mode of heat transfer in solids
conduction
Internal energy is tied to the ____ of a system
temperature
for an incompressible substance, c_p =
c_v = c
delta U of an ideal gas =
mc_vdeltaT
The 1st law states
energy is conserved
A reversible process is ______ concept
an ideal
Irreversibilities may be ____ and/or ____
internal; external
A thermal reservoir is….
a body at constant temp while its energy changes; ideal object
A polytropic process is described by
p*V^n = constant
A quasi-static process is…
a process that happens infinitely slowly
A quasi equilibrium process is…
a quasi-static process in which the system is always in equilibrium (ie. slow expansion or compression)
For expansion and contraction of gases, Work =
area under PV curve
change in total E for a cycle =
0
For a cycle, average rate of E_in =
average rate of E_out
Delta (any property) = 0 for
a cycle
A power cycle…
converts heat to work
Examples of irreversibilities
electrical resistance; friction; mixing of liquids or vapors, plastic deformation
Efficiency of a power cycle =
W_net out/Q_heat in from warm reservoir
COP_Refrig =
QL/W_net in
COP_heat
QH/W_net in
Is the reverse of the Kelvin Plank statement true?
Yes
Can carnot efficiencies be applied to individual processes?
No, only cycles
If the SCI = 0 then system is
internally reversible
An impossible system has an SCI …
< 0
SCI gives a measure of …
irreversibilities and relative inefficiencies
Units of entropy
kJ / K
Entropy production is a measurement of…
the irreversibilties in a given process
Can sigma_p < 0 ?
NO
If there is heat flow out of your system, system entropy should
decrease
Can SCI be applied to individual processes?
NO
Is entropy conserved?
NO
Can entropy balance be applied to processes?
YES
