Thermodynamics Flashcards
Extensive properties
Capacity factors
Depend on the amount of matter present in terms of mass
They are equal to the sum of the parts/ additive
EX: total volume/total energy of a system
State properties
Defines state of a system
Properties are interrelated
Does not depend on path taken
Temperature, pressure, volume, internal energy, enthalpy, entropy
Path functions
Such as heat (Q) and work (W).
Path dependent properties
I exact differentials
Intensive properties
Intensity factor do not depend on the quantity of material present
I.e. Temperature, viscosity, molar volume, density, pressure, refractive index
At equilibrium they are the same for every pet of the system
Equation of state
Equation that relates the thermodynamic properties of a system in a state of equilibrium
Simplest: PV = nRT
State of equilibrium
Thermal equilibrium
Mechanical equilibrium
Chemical equilibrium
Chemical equilibrium
The chemical composition of the system does not vary
Mechanical equilibrium
The pressure is the same everywhere in the system
Isobaric
Occurring at constant pressure
Constant P
Isochoric
Occurring at constant volume
Constant V
Isothermal
Occurring at constant temperature
Constant T
Adiabatic
Occurring with no exchange of heat between the system and its surroundings
Q = 0
Cyclic
Initial state = final state
Adiabatic processes
Is enclosed by an adiabatic boundary = temperature is independent of its surroundings
Never achieves thermal equilibrium with its surroundings
I.e. Flow of heat through the boundary = 0
Ideal gas
Composed of gases in random motion
Collision are perfectly elastic
Molecules don’t attract each other
U depend only on T and # of molecules
Internal energy (U)
Sum of the energies of the sons Titus the molecules
Van der Waals Equation
((P+an^2)/V^2) (V-nb) = nRT
a = constant for force of interactions b/w gas particles
b = constant for excluded volume
Work and heat
Delta U = Q + W
Work
W = -Pext (Vf-Vi)
Involves the movement of matter
W = PdV for reversible processes
Heat
Is thermal energy that flows from a hot body to a cold one
Stored as kinetic and potential energy
If Q is added to a system
Q = (+)
Heat is removed from a system
Q = (-)
If work is done on a system
W = (+)
If work is done by a system
W = (-)
1st Law of Thermodynamics
The total energy of a system and its surroundings is always constant
1st Law of Thermodynamics
U = Q - W I = total internal energy Q = heat added to the system W = work done by the system dU = Q - W
Adiabatic process and 1st Law
U = -W Q = 0
Enthalpy
H = U + PV
dH = dU + d(PV) = dU + PdV + VdP
Constant pressure: dH = dU + PdV
Heat capacity (Cp & Cv)
The thermal energy that must be added to raise the temperature of a system by 1 C, under specific conditions
Can calculate heat capacity of reversible processes, for which the path is fully specified
Heat capacity at constant volume (Cv)
Cv = (dQ/dT)v
Under this restriction: W = 0
Under this restriction: dU = dQ
Cv = (dU/dT)v
Heat capacity at constant pressure (Cp)
Cp = (dQ/dT)p
Cp= (dH/dT)p
Cp is a system property
Cp & Cv written in other forms
dU = CvdT
dH = CpdT
Always valid for ideal gas
Cp & Cv at low pressure
Real-gas behavior in low pressure resembles idea gas so P -> 0 limit
Cp - Cv = R
R = gas constant
Ratios of heat capacities
Y = Cp/Cv
R/Cv = Y - 1
Ideal gas state
State achieved when a real gas is compressed to a finite pressure while retaining ideal gas behavior
Ideal gas heat capacities
igCv = (3/2)R igCp = (5/2)R Y = 1.67
Ideal heat capacities for diatomic gases
igCv = (5/2)R igCp = (7/2)R Y = 1.40
