Thermodynamics Flashcards
What is temperature on a molecular scale
total of vibrational, rotational, and translational energies
amount of molecular movement; thermal energy per mole of molecules
In gas and liquid, what is the main determinant of temperature out of the three energies that contribute to thermal energy?
translational energy in 3D
tarnslational energy (moving the center of mass) depends on degrees of freedom or modes (3)
What is the average kinetic energy per mole of molecules
3/2 * RT
How does increase in temperature affect the volume for gases of different pressures?
In a Volume vs. Temperature graph, where do the lines of different pressures of gas intersect?
At 1 atm at 273K (0C), what is the molar volume of 1 mole of gas molecules?
directly proportional - positive linear relationship for all gases at different pressures but with different slopes
gases at different pressures will extrapolate and intersect at absolute 0 K
22.4 L
What is pressure in terms of force and kinetic energy?
Specifically, what kind of kinetic energy is pressure?
Force over an area
Random translational kinetic energy of a group of molecules per volume occupied
How do you define an internal energy and what are the two component that make up the internal energy?
sum of “kinetic and internal energy in a system - collective energy within a system, not the motion or position of the system
Kinetic energy portion: rotational, vibrational, translational
Potential energy portion: electronic (potential electrical energy created b the attractions between electrons and their nuclei), intermolecular potential energy, rest mass energ (E=mc^2).
What component of internal energy is the only thing that can change in an ideal gas? what about for a real gas?
Translational energy; therefore, temperature is the only component of internal energy that can change
for a real gas, any change in the components of internal energy can cause a change
What is heat
Random collisions between molecules of two systems where energy is transferred from higher to lower energy molecules.
what does it mean to reach equilibrium for two systems in terms of molecular collisions
there are still collisions happening but there is no transfer of energy. the two systems have the same temperature and kinetic energy
what is conduction
thermal energy transfer via molecular collisions (actual physical conditions)
what does thermal conductivity of conduction depend on
it depends mainly on composition and to a less degree on temperature
what is convection?
what drives the movement of fluid and in what direction does it flow?
what is an example
transfer of thermal energy via a fluid
different in pressure or density drive the warm fluid in the direction of cool fluid
circular current of air carrying the heat (ocean and air currents)
what is radiation
what objects radiate heat?
thermal energy transfer via electromagnetic waves
all objects with a temperature radiate heat (above 0 K)
what is power in terms of radiation
rate of heat transfer via radiation or electromagnetic waves
what affects the rate of thermal energy transfer via radiation?
it depends on fraction of heat absorbed, surface area, and different in temperature
mainly on temperature difference
in radiation, what does it mean when an objects has an emissivity of 1?
absorbs everything, appear black
black body radiator is only in theory
what is the only transfer of heat that can occur through a vacuum?
radiation
what does it mean when a system does work?
what does it mean on a molecular level?
the system changes in size or shape while position remains the same - there must be a change in volume so it is said to do PV work
on a molecular level, it is a directional collision of molecules
what is the capacity to do work?
what about unconstrained system with infinite volume?
arises from constraints of molecules like piston
unconstrained system like ideal gas with infinite volume can do no work
how to define whether or not the energy transfer is heat or work
depends on the effect of the surrounding
random collisions on the surrounding is heat
ordered molecular collisions on the surrounding is work
Is enthalpy conserved
nope
what is enthalpy
theoretical concept that calculates heat transferred assuming that there is no non-PV work done under constant pressure.
∆H = ∆U + P∆V ∆H = (non-PV work - P∆V + q) + P∆V ∆H = non-PV work +q
when there is constant pressure and assuming no non-PV work is done: ∆H = q (constant pressure, closed system at rest)
for an ideal gas, what does the enthalpy depend on
enthalpy depends only on temperature for an ideal gas
types of work that a system at rest can do
PV work and non-PV work
what is a non-PV work
electrical work, twisting work, polarization work, and etc
is work a state function
work is not a state function and depends on the thermodynamic path taken
sign conventions for work:
work done by the system
work done on the system
work done by the system -ve
work done on the system +ve
what is electronic energy
the attractive energy between the nucleus and electrons as a part of internal energy
explains the phenomenon in electron absorption and emission.
greatest change that occurs when there is a chemical reaction
what is intermolecular potential energy
energy created by intermolecular forces between molecular dipoles
becomes significant at high pressure for gases. Makes up a substantial portion of internal energy in liquids and solids
what is rest mass energy
E = mc^2
∆G at equilibrium
0
∆S of the universe at equilibrium
0
is gibbs energy conserved?
not conserved and extensive property
what does gibbs free energy represent
What is gibbs free energy useful for analyzing?
maximum non-PV work available from or free for a reaction. Maximum amount of energy released by a process occurring at constant temperature and pressure that is available to perform useful work.
Contracting muscles, transmitting nerves, and batteries do only non-PV Work so Gibbs energy is useful for analyzing these systems
what is the standard state condition for temperature, pressure, and molarity for aquesous solutions at which enthalpies and gibbs free energy are defined?
25C (room temperature) at 1 atm or 1 barr
1 M for aqueous solutions
what is Gibbs free energy?
free energy to do non-PV work like electronic work
H - TS
what does it mean when the reaction is spontaneous?
reaction starts immediately
does molality change with temperature?
does molarity change with temperature?
Molality does not change with temperature because it measures moles per kg
molarity does change with temperature because change in temperature causes a change in volume
what is a colligative property
property that depends on the amount, not the kind
way to increase heat transfer through conduction
greater temperature difference, shorter, and fatter
T^4
way to increase heat transfer through radiation
increase surface area and the temperature difference
T^4
can thermal energy be completely converted to work in cyclical process?
thermal energy cannot be completely converted to work. it is the second law of thermodynamics
can 0 K exist?
0K cannot theoretically exist
equation for enthapy
equation for enthalp with no change in volume
what is the enthalpy generally for liquids and solids?
internal energy + PV work
with no change in volume, it is just change in internal energy
for liquids and solids, it is generally equal to heat under constant pressure
enthalpy of pure elements at standard condition
at standard condition of 25C, 1 atm, and 1 M, the enthalpies of pure elements are 0
What is the main contributor of change in kinetic energy in a gas?
translational energy
What are examples of two path way dependent functions?
work and heat?
What are the 7 thermodynamic state functions?
Internal energy, U Temperature, T Pressure, P Volume, V Enthalpy, H Entropy, S Gibbs Free Energy
If you know three macroscopic properties of a one-component system in equilibrium and at least _____ of them is extensive, you can find all of the other properties
extensive
What is electronic potential energy?
The potential energy created by the attractions between electrons and their nuclei
In a chemical reaction, changing what type of potential energy accounts for the greatest change in internal energy?
What can you say if this energy remains constant?
Changing the electronic potential energy accounts for the greatest change in internal energy
If electronic potential energy remains constant, we can say that there is no chemical reaction.
What is intermolecular potential energy?
For which phases is the intermolecular potential energy make a significant contribution?
For gases, when can intermolecular potential energy make a significant contribution?
Potential energy created by intermolecular forces between molecular dipoles.
Intermolecular potential energy is significant for solids and liquids. But it can be for gas at higher pressure when the gas molecules are close together where attractive forces become significant.
Is Internal energy a state function?
YES
Is Gibbs free energy extensive or intensive property?
Extensive
The standard free energy change for a reaction from the equilibrium constant Keq
-RT ln Keq
Free energy change reflective of where it is in the path to equilibrium
RT (ln Q/ Keq)
Change in entropy for a reversible reaction
Qrev/T
When energy is distributed into a system, the entropy increases. When energy is distributed out of a system at a given temperature, the entropy decreases.
Cp vs. Cv
Cp > Cv
Specific heat
Amount of heat required to raised the temperature of 1 g of substance by 1 C or 1 K.
Specific heat vs. heat capacity
Specific heat - cal/g*K
Heat capacity - cal/K (specific heat times mass)
Example of constant pressure calorimeter
Example of a constant volume calorimeter
Coffee cup
Bomb calorimeter - no work is done (constant V). Also Adiabatic because no heat is exchanged wrt outside the bomb calorimeter. Heat only exchanged between the vessel and the surrounding water
Isothermal process
Constant temperature
Steep hyperbolic curve placed above Adiabatic process on PV graph.
No change in internal energy means Q absorbed = W done by the system.
Adiabatic process
Constant heat
Work only.
Hyperbolic curve placed lower than the isothermal process on the PV Graph
Isobaric process
Constant pressure
Nice rectangle to find a curve on PV graph
Q = enthalpy
Zeroth Law of Thermodynamics
Q system = -Q sure
Second law of thermodynamics
Strive toward thermal equilibrium
Change in entropy = Qrev/T at a specific temperature
Objects in thermal contact (but not in equilibrium) will exchange heat energy such that object with higher heat energy will give off heat until the objects are in thermal equilibrium
Reversible reaction
A slow process where the system is always in equilibrium so no energy is lost or dissipated
Every natural process is irreversible but certain equilibrium processes such as phase changes can be treated as reversible
In a reversible reaction, what is change in entropy of surrounding plus the change in entropy of the system?
ZERO
Internal Energy Equations
3/2 (P∆V) = 3/2 nkT = 3/2 NRT
Molar Cp - Molar Cv = ?
R
Molar Cv = ?
Molar Cp = ?
Molar Cv = 3/2
Molar Cp = 5/2
The main type of internal energy for a monatomic gas
Translational kinetic energy
Monoatomic gases do not have rotational or vibrational energies.
Vibrational energy is from vibrations of atoms WITHIN a MOLECULE.
Rotational energy: rotation around a center of mass where one point is fixed and the other atom rotates around this mass
What can you say about a reaction if there is no change in electronic potential energy?
That no “chemical” reaction has taken place. A physical reaction may have taken place but not change in the bonding.
When is the intermolecular potential energy significant?
It’s significant when the molecules are close together as in solids and liquids under high pressure and low temperature for gases
For an ideal gas, what component of internal energy can change? What does it imply?
Translational energy, meaning that an ideal gas is independent of volume and dependent only on temperature
Capacity to do work rises from ______
The constraints of molecules so participles in an infinite volume of space can do no work
Enthalpy and internal energy changes ONLY with ________
Temperature
Standard heat of combustion
Enthalpy change associated with the combustion of fuel
Thermal Expansion for Solids
∆L = å L∆T
Thermal Expansion for liquids
∆V = ß V∆T
Specific heat of water
1 cal/g*K
4.18 J/g*K
1 Cal = ____ cal = _____ kJ
1 Cal = 1000 cal = 4.18 kJ
