MITx Flashcards
Compressibility
β=−1/V*∂V/∂P|T
where |T means temperature held constant
Thermal expansion coefficient
α=1/V*∂V/∂T|P
where |P means pressure held constant
The property of a state function is that it is …
independent of the history of the system
Three facts of reversible processes are:
- For a reversible process, the entire universe,
system and surroundings, are in equilibrium at all times. - Reversible processes violate the arrow of time
- In practice, any reversible process would take forever
A reversible process takes so long that that all microscopic processes that are part of the overall process come to equilibrium.
True
Reversible processes are VERY slow
We use exact differentials (ex: dP, dS):
to denote increments of state variables
when the variable is path-independent
correct
We use inexact differentials (ex: ∂P, ∂S):
to denote increments of process variables
when the variable is path-dependent
The heat capacity at constant volume (Cv) for an ideal gas is
3/2* R
For an ideal gas, Cp =
Cp = Cv + R = 5/2 * R
What is true about heat capacity?
It tells us how much heating is necessary to go from T1→T2
It is path-dependent
It is a property of a material
The 4 major processes of Thermodynamics are:
- isothermal
- isobaric
- isochoric
- adiabatic
Isothermal means …
constant temperature, so the boundary has to be highly thermally conductive to regulate the system and keep it fixed. Also, there has to be a thermal reservoir outside the system.
Isobaric means …
constant pressure
Isochoric means …
constant volume
In an isothermal system, the boundary allows …
heat flow
In an adiabatic process, we can have heating taking place between the materials within the boundary but heat cannot cross the boundary.
True
Heat exchange can happen across the boundary for an isothermal process, but the definition of isothermal is that processes take place at a fixed temperature.
True; for things to happen at a fixed temperature, heat exchange needs to happen first in order to get the same temperature.
Processes that happen out in the open are near isobaric because the atmosphere is good pressure regulator, and it is very difficult to change pressure around an object without a rigid sealed structure.
True
In an isochoric process, there is no work done on the surroundings
True; for the volume to stay constant, we need a rigid structure, and since boundary work is pdV, no change in V means no work
The energy of the universe can’t change.
True
The energy of the universe can’t change. This is a paraphrase of the ____________ law of thermodynamics.
First Law; energy can’t be created or destroyed
The first law is only useful locally; if we define a system, boundary, and its surroundings, we can keep track of everything that goes in and out of the system and see that the change in the system is the difference between what goes in and what goes out.
True
System + surroundings =
universe
The first law, applied to the earth, states that …
the energy of a system plus its surroundings is constant
The three types of energy are …
kinetic
potential
internal
Thermodynamics is all about ________ energy
internal
Processes that change U, the internal energy of a system, are …
work
heating
adding stuff
dU means …
the exact derivative of internal energy
We use exact differentials, eg. dU or dV, for …
state functions
dU =
dU = ᵟQ + ᵟW + μdN
ᵟQ = heat applied to the system ᵟW = work done on the system dN = adding stuff μ = chemical potential
+Q and +W means ….
heat added to system; energy of the system increases
Chemical potential, μ, is …
a state function that captures the change of energy when you change the amount of stuff in the system
According to the first law, if we keep track of what goes into our system, we haven’t created or destroyed energy but only …
changed it, moved it out of the system, or taken it into the system
Heat capacity, Q =
Q = T1∫T2 Cv*dT
In general, Cv varies with temperature, making T1∫T2 Cv*dt nontrivial, but under certain conditions one can approximate Cv as …
a constant with respect to temperature:
Q ≈ Cv(T2-T1)
The molar specific heat capacity of a gas at constant volume (Cv) is …
the amount of heat required to raise the temperature of 1 mol of the gas by 1 °C at the constant volume
The gas constant, R, is …
8.3145 J/(mol*K)
1 atm =
1 atm = 101325 Pa
1 Pa =
kg/(ms^2)
1 N =
kg*m/s^2
1 m^3 =
1 m^3 = 10^6 cm^3
The gas constant, R, [in m^3*atm/(molK)] is …
8.20573 m^3*atm/(molK)
What is the density of pure nickel?
8.71 g/mol = 8.91 g/cm^3
The term “compressibility” is also used in thermodynamics to describe …
the deviance in the thermodynamic properties of a real gas from those expected from an ideal gas
Room temperature is about …
20 degrees celsius
1 N/m^2 =
1 Pa
A polytropic process obeys the relation …
p*v^n = C
where p = pressure
v = specific volume (1/density)
n = polytropic index
C = some constant
A polytropic process obeys the relation p*v^n = C.
The condition of n = 0 represents …
n = 1 represents …
n = ∞ represents …
n = ϒ = cp/cv represents …
an isobaric process
an isothermal process
an isochoric process
an isentropic process
For an isentropic process (n = ϒ = cp/cv), the first law of thermodynamics gives …
du = -v1∫v2 pdv = -Cv1∫v2 v^-ϒ*dv
du = p(v2 - v1)/(ϒ-1) = p/ρ(ϒ-1)
where p = pressure
ρ = density
ϒ = n = cp/cv
Ambient pressure (presión ambiental) means …
the pressure of the surrounding medium, such as a gas or liquid, in contact with the object
If heat capacity is not constant with temperature, we can find ΔT by ….
Q = T1∫T2 Cv*dT
integrating the above and finding the roots
Q = T1∫T2 Cp*dT =
ΔU
Cp for a monatomic gas is …
5/2*R
For a monatomic gas, Q =
Q = (3/2)nRΔT = nCVΔT
The coefficient of thermal expansion describes …
how the size of an object changes with a change in temperature.
The coefficient of thermal expansion measures …
the fractional change in size per degree change in temperature at a constant pressure, such that lower coefficients mean that an object does not expand or contract much with a change in temperature
The definition of cv is …
cv = (∂u/ ∂T)v
The definition of cp is …
cp = (∂h/∂T)p
Q =
Q = CΔT
where C = Cp if constant pressure and Cv if constant volume
cv = (∂u/ ∂T)v and cp = (∂h/∂T)p holds for …
constant volume, constant pressure, or neither
We can assume that nitrogen gas behaves as a monatomic ideal gas under the conditions of …
we have far surpassed the saturation temperature and are in the superheated region (pure gas)
Convert 60 degrees Fahrenheit to Celsius
(60 - 32)*5/9
⁰C = (x⁰F - 32)*5/9
