Thermodynamics Flashcards
Define Energy
Energy is the capacity to do work [ J ]
Define Work
Work is a form of energy which can transfer in and out of a system, stored in the organized motion of molecules [ W ]
Work is done when an object is moved against an opposing force
What is the Work equation
Work = Force * Distance
OR
dW = -Pex * dV (Pex = F/A)
Define Heat, Q
Energy of a system changed by means other than work [ J ]
Define a Diabatic (Diathermic) System
A Diabatic system is where energy is allowed in and out in the form of heat
(system in THERMAL CONTACT with surroundings)
Define a Adiabatic System
An Adiabatic System is where heat is NOT allowed in or out
(Isolated wall)
Wsystem > 0 means:
Work done by the system on the surr
Work done on the system by the surr
Work done on the system by the surr
system is SELFISH likes to GAIN W&Q
Qsystem > 0 means:
Heat transferred from system to surr
Heat transferred on the system by the surr
Heat transferred on the system by the surr
system is SELFISH likes to GAIN W&Q
Define Internal energy
- The total energy of the system
- It is a STATE FUNCTION: depends on current state
- It is an EXTENSIVE PROPERTY: depends on amount of matter
There must be a change in _______ for a change in internal energy
There must be a change in TEMPERATURE for a change in internal energy
What is the First Law of Thermodynamics
(Internal energy equation)
ΔU = Q + W
(heat to system & work done on system)
ΔU equation
ΔU = Ufinal - Uinitial
2) Isobaric Process effect on ΔU = Q + W
Pressure is constant
ΔU = Q + W
Isochoric Process effect on ΔU = Q+ W
Volume is constant
No area under curve for P/V graph, no U
ΔU = Q
Adiabatic Process effect on ΔU = Q + W
No transfer of heat in the system, ΔQ = 0
ΔU = Wad
Isothermal Process effect on ΔU = Q + W
Temperature is constant, ΔT = 0 ∴ ΔU
Q = -W
Cyclic Process (e.g. engines) effect on ΔU = Q + W
Same initial and final stages, ΔU = 0
Q = -W
Define a Reversible process
A Reversible process is never more than INFINITESIMALLY FAR from EQUILIBRIUM and an infinitesimal change in EXTERNAL conditions can REVERSE the process.
What are Reversible Expansion conditions
net F = Fgas - Fex = 0
Pex = P,
Pex (external pressure)
Define a Irreversible process
A Irreversible process CANNOT be reversed by a INFINITESIMAL change in EXTERNAL conditions
What is the Ideal gas equation
PV = nRT
What is the Non-ideal gas equation
PV = ZnRT
Z is the compressibility factor / Van Waals eq.
What is an indicator diagram
P/V graph to calculate expansion work
How to study changes in energy due to heat
- Calorimetry studies
- Heat capacities and enthalpies
Define Heat capacity
Heat capacity is the heat required to raise the temperature of the system by one kelvin
What does the slope of U/T graph give
The HEAT CAPACTIY of the system at that TEMPERATURE
A change in internal energy can be identified with the ____ supplied at a constant volume
A change in internal energy can be identified with the HEAT supplied at a constant volume
Qv = CvΔT
Define Enthalpy
Enthalpy is the internal energy req. to CREATE a system (U) & amount of energy req. to MAKE ROOM for it (PV)
Is a STATE FUNCTION => INDEP. OF PATH
(What is the Cp and Cv relationship)
Cp - Cv = nR
What changes occur when gas expands adiabatically
*****SLIDE 9 L3
1) T= const, V increases U const
2) T reduces, V= const.
What is the perfect gas law
PiVi / PfVf = Ti / Tf
Define Standard enthalpy change
Is the change in enthalpy for a process in stnd states
Define Standard state
Standard state is 298K and 1bar
Define Standard enthalpy of transition
Standard enthalpy of transition is the enthalpy change accompanying a PHASE CHANGE in stnd states
Define Standard reaction enthalpy
Is the change in enthalpy when reactants change to products in stnd states
Define Hess’ Law
The standard enthalpy of an overall reaction is the sum of the standard enthalpies of the individual reactions
Define Exact Differentials
Exact Differentials are systems taken along a path (STATE FUNCTION)
Define Inexact Differential
When a system is heated, total energy transferred as heat is sum of individual contributions along each point of the path
(PATH FUCTION, DEP. ON PATH)
Define Standard enthalpy of formation
Change in enthalpy for formation of compound from its CONSTITUENT ELEMENTS in their reference states.
Define Spontaneous changes
Spontaneous changes are accompanied by dispersal of energy into a more disordered form
Define Non-spontaneous changes
Non-spontaneous changes require something ‘SPECIAL’ to happen
Define the Second Law of Thermodynamics
No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work
What does increasing Entropy do
(2nd Law of ThermoD.)
Increasing Entropy increases DISORDER and RANDOMIZED MOTION
What does negative value of entropy mean
Becomes less disorders, energy must be provided, NON SPONTANEOUS
How to prove Entropy as a State Function
1) dQrev/Trev = 0 true for CARNOT CYCLE
2) “ true for ANY SUBSTANCE
3) “ true for ANY CYCLE
What is the Carnot Cycle ***
1) Reversible isothermal expansion (Th)
2) Reversible adiabatic expansion (Th -> Tc)
3) Reversible isothermal compression (Tc)
4) Reversible adiabatic compression (Tc -> Th)
Look up picture L6 S14
True of any cycle L6 S20??
huh??
What are the states in decreasing disorder
Gases > Liquids > Solids
Define the Third Law of Thermodynamics
As T approaches 0, the absolute entropy tends towards zero
No spatial disorder
No thermal motion
What are Third Law Entropies
Entropies reported on the basis that S(0) = 0,
S°(T)
