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Chemistry 467
Quiz Concepts for P Chem
191
Chemical Engineering
Undergraduate 3
11/25/2012
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Term
What kind of interactions occur when the Henry's law constant is greater than the pure vapor pressure?
 Definition
Unfavorable (repulsive) interactions
Term
The Raoult's law standard state is a physically realizable state
 Definition
True
Term
The Henry's law standard state is a physically realizable state
 Definition
False
Term
Fugacity is to pressure as activity is to (blank).
 Definition
Concentration
Term
What do we call the system when a reacting system has fully equilibrated?
 Definition
Equilibrium
Term
What is the heat of mixing for an ideal mixture?
 Definition
Zero
Term
If DeltaVmix is negative, what does that tell you about the interactions between the components of the mixture?
 Definition
They are generally favorable (attractive)
Term
Write the mathematical expression for chemical potential for a component in an ideal mixture
 Definition
mu=mu* + RT ln(x)
Term
If a mixture follows Raoult's Law, describe the interactions between the different molecules
 Definition
They are the same as between themselves (behaving as though pure)
Term
What happens to the boiling point of a mixture compared to the pure solvent (nonvolatile solute)?
 Definition
Rises
Term
Write the definition of chemical potential
 Definition
mu=(dG/dn)T,p,n
Term
At a given temperature and pressure, which phase is thermodynamically preferred?
 Definition
The one with the lowest chemical potential
Term
Write the fundamental equation of chemical thermodynamics
 Definition
dG=-SdT+VdP+sum(mudni)
Term
As pressure is increased, what happens to the boiling point of a liquid?
 Definition
It increases
Term
What property drives mixing for an ideal mixture?
 Definition
Entropy
Term
Does the Gibbs energy increase or decrease with an increase in pressure?
 Definition
Increases, because (dG/dP)T=V and V is positive
Term
If a reaction is exothermic, what happens to DeltarG if the temperature increases? Think Le Chatelier
 Definition
DeltarG will increase
Term
Why do we need fugacity
 Definition
To account for the behavior of real gases (attractions, repulsions)
Term
Under what conditions are two phases in equilibrium?
 Definition
When they have the same chemical potential (or molar Gibbs energy)
Term
What is the maximum number of phases that can coexist at a particular temperature and pressure?
 Definition
3
Term
Write the fundamental equation of thermodynamics
 Definition
dU=TdS-pdV
Term
Write the Gibbs equation (derived from the fundamental equation) for the Gibbs energy
 Definition
dG=-SdT+VdP
Term
What are the natural variables of the Gibbs energy?
 Definition
temperature and pressure
Term
Why is the Gibbs energy a useful quantity?
 Definition
It tells us the maximum non-expansion work a process can produce; how much of the energy is 'useful'
Term
Does the Gibbs energy increase or decreases as the temperature increases?
 Definition
Decreases, because dG/dT,p=-S
Term
How o you maximize the efficiency of a Carnot engine?
 Definition
Create the largest temperature difference between the hot and cold parts of the engine
Term
What is DeltaSuniverse fora phase transition at its normal transition temperature?
 Definition
0
Term
Briefly explain why all processes are treated as reversible for the surroundings
 Definition
Because the surroundings are infinitely massive compared to the system.
Term
Is DeltaSuniverse for a spontaneous, irreversible adiabatic expansion positive, negative, or zero?
 Definition
positive, the process is spontaneous
Term
Write the definition of Gibbs energy
 Definition
G=H-TS
Term
What is the sign of DeltavapH for any material?
 Definition
Positive, it takes an input of energy to vaporize something
Term
Write the thermodynamic definition of entropy
 Definition
dS=dqrev/T
Term
What makes a process spontaneous?
 Definition
DeltaSuniverse increases
Term
True or False: the entropy of the system can spontaneously decrease
 Definition
True
Term
True or False: the entropy of all substances is zero at zero Kelvin
 Definition
False
Term
What is DeltaU for any isothermal process involving ideal gas?
 Definition
Zero
Term
What is DeltaU for any cyclic process?
 Definition
Zero
Term
What do we mean when we say an expansion process is reversible?
 Definition
p=p,ex throughout the process, no net work for the process and its opposite
Term
Which process produces more work? reversible isothermal expansion of ideal gas or reversible adiabatic expansion of ideal gas?
 Definition
Reversible isothermal expansion of ideal gas produces more work
Term
When two objects are at different temperatures and then placed in thermal contact, in which direction does heat flow?
 Definition
from the hot to the cold
Term
On what variables does the internal energy of an ideal gas depend?
 Definition
Only on Temperature
Term
Write the total differential of internal energy as a function of temperature and volume, U(T,V)
 Definition
dU=(dU/dV),T*dV+(dU/dT),V*dT
Term
Write the definition of the constant volume heat capacity
 Definition
C,v=(dU/dT)v
Term
Write the definition of enthalpy
 Definition
H=U+pV
Term
What is meant by an adiabatic process?
 Definition
One in which no heat flows between system and surroundings.
Term
What cna a closed system exchange with the surroundings?
 Definition
Energy but not matter
Term
The Zeroth Law of Thermodynamics helps us to define what kind of Equilibrium?
 Definition
Thermal Equilibrium
Term
Generally speaking, what physical quantity is the First Law of Thermodynamics Concerned with?
 Definition
Energy, or internal energy
Term
Provide a brief explanation of the difference between heat and work at the molecular level?
 Definition
Work involves organized motion of the molecules; heat involved random motion
Term
Write the mathematical definition of expansion work
 Definition
dwexp=-pexdV
Term
Write the general expression for the chemical potential as a function of conditions.
 Definition
mu=mu^not+RTln(a)
Term
Write the general form of the reaction quotient, Q
 Definition
Q=product(a^nu)
Term
Write the relation between the equilibrium constant and the standard reaction Gibbs energy, DeltaGreaction
 Definition
DeltaGreaction^not=-RTln(K)
Term
What is the value of the reaction Gibbs energy when the reacting system is at equilibrium?
 Definition
DeltaGreaction=0
Term
If a reaction is exothermic, in what direction will it shift with an increase in temperature?
 Definition
Toward the reactants.
Term
True or False: The equilibrium composition of a gas phase reaction can change when the vessel is compressed at constant temperature.
 Definition
True
Term
True or False: The equilibrium constant of a gas phase reaction can change when the vessel is compressed at constant temperature.
 Definition
False
Term
True or False: The equilibrium constant of a reaction generally changes with temperature.
 Definition
True
Term
Write the general expression for the reaction Gibbs energy as a function of conditions
 Definition
DeltaGrxn=DeltaGrxn.not+RTln(Q)
Term
What is the key difference between standard conditions and standard biological conditions?
 Definition
Standard biological conditions are at pH 7, [H+]=1*10^-7 molar, 1 molar
Term
True or False: A transition state is a stable molecular configuration that can be isolated and studied
 Definition
False
Term
Is the mathematical shape of the transition state a maximum, minimum, or saddle point on the potential energy surface?
 Definition
Saddle Point
Term
To spectroscopically probe a transition state, what time scale of pulses do we need?
 Definition
Femtosecond
Term
What is the sign of DeltaS(doubledagger)?
 Definition
Negative
Term
What is the sign of DeltaG(doubledagger)?
 Definition
Positive
Term
List three state variables that we use to describe the physical properties of a gas?
 Definition
T,p,V and n
Term
The Zeroth Law of Thermodynamics defines what type of equilibrium?
 Definition
Thermal Equilibrium
Term
Name one of the scientists whose work led to the development of the ideal gas law?
 Definition
Boyle, Charles, Gay-Lussac, Avogadro
Term
Under what conditions of temperature and pressure do the ideal gas law hold true?
 Definition
Low pressure and high temperature
Term
Upon what was the development of the Ideal Gas Law based?
 Definition
Experimental observation and proposed principles
Term
What happens to the width of a probability distribution as the number of trials increases?
 Definition
The width narrows
Term
How do we calculate the average of a property described by a continuous probability density function?
 Definition
h_bar=integral(h*f(h)dh)=
Term
Define what is meant by an ensemble?
 Definition
A collection of individual items such as molecules
Term
Consider placing balls in boxes. We put 2 balls in the first box, 1 in the second, and 1 in the third. Assuming all the balls are identical, and the order doesn't matter, what is the statistical weight of this arrangement?
 Definition
W=4!/(2!1!1!)=12
Term
What is the statistical weight if all four balls are in the first box (of three)?
 Definition
W=4!/(4!0!0!)=1
Term
According to the principle of equal a priori probabilities, which of these two arrangements (all balls in one box or some in all three) is preferred?
 Definition
Neither is preferred
Term
State one of the constraints of the Boltzmann distribution
 Definition
Fixed number of molecules in the system; fixed total energy in the system
Term
State the two constraints that lead to the Boltzmann distribution
 Definition
Fixed number of molecules; fixed total energy in the system
Term
Write the mathematical expression of the partition function
 Definition
q=sum(e^-E_i/kT)
Term
Write the Boltzmann expression for entropy in terms of statistical weight
 Definition
S=kln(W)
Term
What does it mean when two states are said to be 'degenerate'?
 Definition
They have the same energy
Term
Consider a container of Ar gas. What happens to the average speed of the Ar atoms as the temperature increaseS?
 Definition
The average speed increases.
Term
At a molecular level, what is the source of the pressure of a gas?
 Definition
Collisions between the gas molecules and the walls of the container
Term
Consider two samples of gas, He and Ar, at the same temperature. In which sample are the atoms, on average, moving faster?
 Definition
He, the average speed increases as the mass decreases.
Term
State one of the assumptions in the kinetic molecular theory of gases, as we treated it.
 Definition
Molecules are in ceaseless, random motion; gas molecules have no size; all collisions are elastic.
Term
Describe what is meant by the term "mean free path"
 Definition
The average distance a molecule travels before experiencing a collision.
Term
What term do we use to describe the transfer of matter through another medium (such as a gas)?
 Definition
Diffusion
Term
If the pressure decreases, but the temperature stays the same, what happens to the collision density?
 Definition
The collision density decreases; there are fewer collisions.
Term
If there is a sharp change of concentration with distance, in what direction will diffusion occur?
 Definition
In the direction of the region with lower concentration.
Term
Name one other property besides diffusion that is correctly predicted by the kinetic molecular theory of gases:
 Definition
Viscosity, thermal conductivity
Term
What must phsyically happen between two molecules in order for a reaction to take place?
 Definition
Collision
Term
A reaction is found to have the rate law v=k[A]^2. What is the order of the reaction?
 Definition
Second order
Term
True or False: The rate of a reaction can be either positive or negative.
 Definition
False, reaction rates are always positive.
Term
At a molecular level, what does the activation energy represent?
 Definition
The minimum energy required for a collision to lead to reaction.
Term
True or False: If I know the overall reaction, I can write down the rate law?
 Definition
False, rate laws MUST be determined experimentally.
Term
What is meant by the term "half life"?
 Definition
The time it takes for the concentration of a reactant to drop by half the initial value.
Term
IF a reaction follows first order kinetic, how should I plot the data to determine the rate constant?
 Definition
As ln[A] vs. t
Term
If a reaction takes place through a bi-molecular mechanism, what order will the rate law be?
 Definition
Second order, of the form v=k[A][B]
Term
If we have a branching reaction that is under kinetic control, which product is more likely to be formed?
 Definition
The one with the larger rate constant.
Term
If we have a branching reaction that is under thermodynamic control, which product is more likely to be formed?
 Definition
The one with the larger equilibrium constant.
Term
In the steady state approximation, what do we assume about the concentration of an intermediate?
 Definition
The concentration does not change with time: d[I]/dt=0
Term
Briefly describe how a catalyst speeds up a reaction
 Definition
By lowering the activation energy, or providing an environment that allows the reactants to interact in a way that favors production of product.
Term
What step(s) generally determine the rate of reaction, fast or slow?
 Definition
Slow
Term
What kind of chemical species is commonly involved in chain reaction mechanisms?
 Definition
Free radicals
Term
In the Langmuir model, how deep can a surface be covered?
 Definition
One monolayer
Term
What is one of the two types of energy we have from Newtonian mechanics?
 Definition
Kinetic, potential
Term
Name one type of molecular motion that contributes to the heat capacity.
 Definition
Translational, vibrational, rotational.
Term
How much does each rotational degree of freedom contributes to the heat capacity?
 Definition
1/2R
Term
How many degrees of freedom does NH3 have?
 Definition
3N=12
Term
How many vibrational degrees of freedom does NH3 have?
 Definition
3N-6=6
Term
What quantity do we use as our 'energy ruler' in determining whether an energy state is high or low
 Definition
The quantity k.bT (or RT in molar units)
Term
Name or describe one phenomenon that led to the development of quantum mechanics?
 Definition
Blackbody radiation, heat capacity of solids, photoelectric effect, electron diffraction
Term
What did Einstein's explanation of the photoelectric effect tell us about light?
 Definition
Light can act like a particle, or the energy is quantized.
Term
What was de Broglie's hypothesis about the behavior of particles?
 Definition
Particles should behave like waves to some degree
Term
Name an experiment that proved de Broglie correct?
 Definition
Electron diffraction, two-slit experiment
Term
How do we mathematically describe the behavior of a particle in quantum mechanics?
 Definition
With a wavefunction
Term
What does the Hamiltonian operator account for?
 Definition
Total energy, kinetic plus potential
Term
What does the quantity psi*psi tell us about?
 Definition
The probability of finding the particle between x and x+dx
Term
State one of the requirement of a wavefunction?
 Definition
Continuous, continuous first derivative, square integrable, single valued, finite
Term
If we have a free particle (no forces acting on it) that is described by a single value of momentum, where is the particle located?
 Definition
It has no location, it is delocalized over all space
Term
In the formalism of quantum mechanics, how do we represent a physically measurable quantity?
 Definition
With the corresponding quantum mechanical operator.
Term
How do we determine the expectation value of a physically observable quantity?
 Definition
Evaluate =integral(psi*j_hat*psi d(tao)
Term
If a wavefunction is not an eigenfunction of a given operator, how should I write it?
 Definition
As a linear combination of eigenfunctions of that operator.
Term
If a wavefunction is a linear combination of two eigenfunctions of the Hamiltonian, what values of energy can we measure?
 Definition
We can only measure one of the two eigenvalues.
Term
True or False: Before an individual measurement on the wavefunction (in this case, a linear combination of two eigenfunctions of the Hamiltonian), I can predict the energy I will measure.
 Definition
False: I can predict the probability of each measurement, but not individual measurements.
Term
After measuring the energy of the wavefunction in question 2, what happens to the wavefunction?
 Definition
The wavefunction 'collapses' to the eigenfunction corresponding to the measured energy.
Term
What does it mean to say that two operators do not commute?
 Definition
The result of the measurements will be different depending on the order in which the measurements are performed.
Term
What is a postulate?
 Definition
Something we assume to be true and use for further reasoning.
Term
For the particle in a box, what happens to the energy as the size of the box decreases?
 Definition
Energy increases.
Term
For the n=1 state of the particle in a box, what is probability of finding the right particle right next to the wall of the box?
 Definition
Zero
Term
True or False: A particle confined to a box can have zero energy
 Definition
False; if the energy is zero, there is no particle in the box.
Term
If I want to cause a transition between two energy states, what must the frequency of the incident light be?
 Definition
v=DeltaE/h; the incident light has to match the difference in energy of the two states.
Term
What are the two conditions that must be met for a spectroscopic transition to occur?
 Definition
The energy of the photon must match the energy difference between the states. The transition dipole moment must be non-zero; the transition must be allowed.
Term
In the classical limit, what does the probability density function look like for the particle in a box?
 Definition
Uniform probability of finding the particle anywhere in the box.
Term
Why don't we worry about quantum effects when talking about an ideal gas?
 Definition
The size of the container is so large that the energy levels can be treated as a continuum; or the molecules are so far apart that they don't have any quantum interactions.
Term
State one practical application of tunneling
 Definition
Schottky or tunneling diode; proton transfer; nuclear fusion; electron microscopy
Term
Which are more likely to tunnel through a barrier, electrons or protons?
 Definition
Electrons, because of their smaller mass.
Term
True or false: After tunneling through a barrier, a particle has less kinetic energy
 Definition
False; the energy is unchanged. The amplitude of the wavefunction, or the probability of being on the other side of the barrier, is reduced.
Term
If we isotopically substitute deuterium for hydrogen, and the rate of reaction decreases, what does that tell us about the rate limiting step?
 Definition
It likely involves proton transfer, or proton tunneling.
Term
In a 3-D situation, what aspect of the system leads to degenerate states?
 Definition
Symmetry
Term
In addition to energy, the rigid rotor illustrates that what physical quantity is also quantized?
 Definition
Angular momentum
Term
In what region of the electromagnetic spectrum do rotational transitions take place?
 Definition
The microwave region
Term
How can we break the degeneracy of rotational states?
 Definition
With an external field, magnetic or electric.
Term
TRue or False: Compared to k.bT, rotational levels are close together?
 Definition
True
Term
Name one type of spectroscopy that allows us to measure vibrational transitions.
 Definition
IR or Raman spectroscopy
Term
How many vibrational normal modes does H2O have?
 Definition
3n-6=3
Term
True or False: a molecule can have no vibrational energy?
 Definition
False, there is always zero point energy of 1/2 h*nu
Term
In what region of the electromagnetic spectrum do vibrational transitions take place?
 Definition
Infrared
Term
True or False: Compared to k.bT, vibrational levels are very close together?
 Definition
False
Term
True or False: Electrons circle the nucleus just like planets orbit the sun.
 Definition
False
Term
Name one atom for which we have solve the Schrodinger equation exactly.
 Definition
Hydrogen (it's the only one)
Term
What do we call solutions to the Schrodinger equation for the hydrogen atom?
 Definition
Atomic orbitals
Term
In what range of the electromagnetic spectrum do we observe transitions between the electronic states of an atom?
 Definition
Visible to UV
Term
What do we take as our zero of potential energy for a hydrogen atom?
 Definition
Infinite separation of the proton and electron
Term
When constructing molecular orbitals from atomic orbitals, h ow many molecular orbitals will we have?
 Definition
The same as the number of atomic orbitals.
Term
We generally talk about two types of molecular orbitals. Name one.
 Definition
sigma and pi
Term
Why doesn't He form a diatomic molecule?
 Definition
The energy would have higher than for two unbonded atoms.
Term
True or False: All molecular orbitals are localized along particular bonds
 Definition
False: Most molecular orbitals are delocalized over the whole molecule.
Term
How does the Born-Oppenheimer approximation treat motion of the nuclei?
 Definition
Nuclei move much more slowly than the electrons.
Term
True or False: If a molecule has a bound ground electronic state, all excited states are also bound.
 Definition
False: Excited states can be unbound. The molecule will dissociate if it is excited to such a state.
Term
Name one process by which an electronically excited molecule relaxes and emits a photon.
 Definition
Fluorescence, phosphorescence, chemiluminescence.
Term
What has a longer lifetime, fluorescence or phosphorescence?
 Definition
Phosphorescence
Term
Why are the lifetimes different for fluorescence and phosphorescence?
 Definition
Because phosphorescence involves a forbidden transition.
Term
What term do we use to describe breaking chemical bonds with light?
 Definition
Photolysis or photodissociation
Term
Will fluorescence occur at longer or shorter wavelengths than the excitation?
 Definition
Longer wavelengths, or lower energy
Term
What quantum mechanical model do we use for translations of molecules when building the partition function?
 Definition
Particle in a box
Term
identify one of the key components of a laser:
 Definition
Gain medium, pump source, resonator cavity
Term
True or False: at room temperature, we can reasonable assume that rotational levels are close together
 Definition
True: the rotational temperature is many times less than T
Term
At the molecular level, what conditions are required for ideal behavior?
 Definition
No interactions (except for collisions)
Term
What do we call a collection of individual microsystems?
 Definition
An ensemble
Term
Given our collection of microsystems, how do we determine bulk properties?
 Definition
By taking the ensemble average of that property: M_bar=sum(M_j*P_J)=(sum(M_j*e^(-E_j/kT)))/Q
Term
What thermodynamic properties do we keep constant in the canonical ensemble?
 Definition
N,V, and T
Term
What is the interaction potential for an ideal gas?
 Definition
E_p=0 (or V=o)
Term
What do we call the temperature below which a gas can condense?
 Definition
The critical temperature
Term
Write the definition of the reduced temperature.
 Definition
T_r=T/T_c
Term
Name one equation of state for real gases
 Definition
van der Waals, virial (Berthelot, Dieterici, Redlich-Kwong)
Term
What happens when a real gas is compressed at a temperature below the critical temperature?
 Definition
It condenses
Term
What do the two parameters in the van der Waals equation account for?
 Definition
Finite volume of the gas molecules and attractive interactions
Term
For a particular gas at ambient in the van der Waals equation account for?
 Definition
Attractive interactions
Term
According to the principle of corresponding states, how do we best compare the behavior of different gases?
 Definition
By comparing the reduced variables
Term
In terms of molecular order, what characterizes the structure of a liquid at short and long distances?
 Definition
Short-range order, long range disorder
Term
What can a closed system exchange with its surroundings?
 Definition
Energy, but not matter
Term
The zeroth law of thermodynamics helps us to define what kind of equilibrium?
 Definition
Thermal
Term
Generally speaking, what physical quantity is the First Law of Thermodyamics concerned with?
 Definition
Energy, or internal energy
Term
Provide a brief explanation of the difference between heat and work at the molecular level?
 Definition
Work involves organized motion of the molecules, heat involves unorganized motion.
Term
Give the mathematical definition of expansion work?
 Definition
delW_exp=-p_ex*dV
Term
On what variables does the internal energy of an ideal gas depend?
 Definition
Only T
Term
Write the total differential of internal energy as a function of temperature and volume U(T,V)
 Definition
dU=(dU/dV)_T*dV+(dU/dT)_v*dT
Term
Write the definition of constant volume heat capacity
 Definition
C_v=(dU/dT)_v
Term
Write the definition of enthalpy
 Definition
H=U+pV
Term
What is meant by an adiabatic process
 Definition
One in which no heat flows between system and surroundings.
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