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PChem1Final
Final test of Physical Chemistry 1-UW Platteville
| Question | Answer |
|---|---|
| the goal of chemical potential is to express | any thermodynamic property of an equilibrium system in terms of easily measured quantities |
| consider the simplest possible system-single phase of pure substance, like liquid water. at the temperature and the pressure of the system chemical potential = | molar Gibbs free energy in a particular phase |
| mui is the | Gibbs energy per mole of component "i", i.e. the partial molar Gibbs free energy |
| partial quantity of partial molar Gibbs free energy | quantity not affected by adding another component but the total is affected |
| Gibbs energy is made up of | chemical potential |
| regardless of the nature of the process, the transfer proceeds from a higher chemical potential | to a lower chemical potential |
| the flow from high to low chemical potential will continue until | chemical potential has been equalized in all phases of the system |
| just like difference in temperature is the driving force for the flow of heat from one phase to another, a difference in chemical potential | is the driving force for the flow of chemical species, i, from one phase to another |
| spontaneous processes go from | high chemical potential to low chemical potential until they reach equilibrium |
| at equilibrium there cannot be | any spontaneous processes so the chemical potentials are equal |
| the chemical potential and its downhill drive to equilibrium will be the basis of the study of | phase transitions, chemical reactions, etc. |
| ex. write the phase equilibrium conditions for a liquid solution of acetone and water in equilibrium with its vapor | you get a mixture w/ some vapor above lq which is a mixture of both components, both components are in equilibrium with it's chemical potential between the two phases but the chemical potential of each component is not equal |
| we know initial Gibbs, but concentration during a reaction is constantly | changing therefore Gibbs energy is constantly changing as the reaction progresses |
| to be spontaneous G has to | <0 so we need (amuA + bmuB) > (cmuC +dmuD) |
| in thermodynamics we try to preserve the form of equations that are developed for ideal systems. This is the thought behind | the introduction of the activity aJ of the substance |
| activity for a pure solid or a pure liquid in the standard state equals | 1 |
| mu nod is the | standard chemical potential |
| for a pure gas at standard state | p/p0 |
| for a pure solute at standard state | [J]/c0 |
| dynamic equilibrium example | cars moving on or off a bridge |
| static equilibrium example | tug of war, equal strength so the rope doesn't move |
| chemical equilibrium is an example of | dynamic equilibrium |
| chemical equilibrium occurs when opposing reactions are proceeding at | equal rates |
| kinetics tell us how fast a reaction | reaches equilibrium |
| opposing reactions naturally lead to | equilibrium |
| equilibrium can be reached by | either direction, reverse or forward reaction |
| Kp | equilibrium constant using partial pressure of gases |
| Kc | equilibrium constant using concentrations |
| large K | lots of products (equation shifts far to the right) |
| small K | lots of reactants (far to the left) |
| homogeneous phase | in the same phase |
| heterogeneous equilibrium | different phases |
| solvents, solids, and liquids are not included when writing | equilibrium constant |
| why are solids and liquids not included when writing equilibrium constant | because they're "constant" and M/v ratio stays constant in the dynamic equilibrium; P-chem level: the activities of (s) and (l) in standard state equal 1 |
| if K=Q | reaction is at equilibrium |
| if K>Q | more reactants |
| if K < Q | more products |
| Le Chatlier's principle | "if a system at equilibrium is disturbed by a change in temperature, pressure, or the concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance" |
| if you increase the amount of reactants | equilibrium shifts to the right |
| Pressure-Volume changes do not | change K as long as temperature is constant they instead change total pressures |
| temperature changes and equilibrium | exo and endothermic process have heat as a product and reactant respectively |
| increase temperature of an endothermic reaction the equilibrium shifts | right |
| increase temperature of an exothermic reaction the equilibrium shifts | left (more reactants) |
| catalysts | lowers activation energy; increase rate of both forward & backward reactions proportionally; doesn't change composition of reaction or K |
| if the reaction is exothermic deltaH < 0 and deltaS>0 | deltaG<0 and K>1 at all temperatures |
| if the reaction is exothermic deltaH<0 and deltaS<0 | deltaG<0 and K>1 provided that T<deltaH/deltaS |
| if the reaction is endothermic deltaH>0 and deltaS>0 | deltaG <0 and K>1 provided that T>deltaH/deltaS |
| if the reaction is endothermic deltaH>0 and deltaS<0 | deltaG<0 and K>1 at no temperature |
| endothermic reaction | deltaH>0 |
| exothermic reaction | deltaH <0 |
| at equilibrium deltaG = | 0; deltaH = TdeltaSnod |
| deltafGnod > 0 is unstable with respect to | its elements |
| spontaneity is a thermodynamic tendency that might not be realized at a | significant rate in practice |
| thermodynamic equilibrium constant is | independent of pressure |
| K is independent of pressure does not mean that the equilibrium composition is | independent of the pressure and its effect depends on how the pressure is applied |
| if the gases are perfect, addition of inert gas leaves all the partial pressures | of the reacting gases unchanged |
| partial pressure of a perfect gas is the pressure it would exert if it | were alone in the container, so the presence of another gas has no effect |
| pressurization by the addition of an inert gas has | no effect on the equilibrium composition of the system (provided the gases are perfect) |
| when a reaction at equilibrium is compressed, the reaction responds by reducing the # of molecules in the gas phase (in this case by producing the dimers represented by the linked spheres) if a system at equilibrium is compressed then the reaction will | adjust to minimize the increase in pressure; reduces the number of particles in the gas phase |
| exothermic reactions | increased temperature favors the reactants |
| endothermic reactions | increased temperature favors the products |
| dependence of the equilibrium constant on the temperature is expressed by the | van't Hoff equation; ln(K2)-ln(K1)=-(deltaH/R)({1/T2}-{1/T1}) |
| for most substances (excluding water and a few other exceptions) the molar volume of the liquid phase is greater than that of the | solid phase |
| for a solid or liquid, the molar volume is almost | independent of pressure therefore to a good approximation: Gm(Pf)-Gm(Pi)=Vm(Pf-Pi) |
| molar volumes of gases are large therefore | Gibbs energy depends strongly on the pressure; Gm(Pf)-Gm(Pi)=RTln(Pf/Pi) |
| using molarities for K only gives you an approximate value because | you're making the assumption it's an ideal dilute solution |
| because the standard states refer to pure materials, the standard chemical potentials in this expression are | the standard molar Gibbs energies of the (pure) species |
| Q refers to an arbitrary stage of the reaction and K | is the value of Q at equilibrium |
| if the concentration of a substance in an equilibrium mixture is 0.010 M, its activity is | 0.010M/1M =0.01 |
| when you replace the activities, the resulting expression is an approximation however | such approximations could be a problem (e.g. electrolyte solutions even when dilute) |
| K=eq constant b/c derived in activities & activities are dimensionless there K | has no units |
| fugacity | activity of a gas |
| the standard state of fugacity, f0 is the | value that the fugacity would have if the gas behaved ideally at 1 bar pressure i.e. f0=P0 |
| f and P are related by fA = gammaAPA where | gamma is the fugacity coefficient |
| as f approaches P, P approaches what and gamma approaches | 0; gamma approaches 1 |
| ] as gamma approaches 1, [A] approaches | 0 |
| what is delta n for: N2O4 (g) yields 2NO2 | 2-1 = 1 |
| for a solid or liquid the molar volume is dependent or independent of pressure | independent |
| phase transitions are changes of phase without change of | chemical composition |
| a substances has a spontaneous tendency to change into the phase with the lowest | molar Gibbs energy |
| below 0 degrees Celsius, water tends to go from lq to s therefore what can be inferred about the chemical potential | mui lq>mui(s) because it goes from high to low chemical potential |
| phase diagrams describe the phase properties as a function of state variables such as | temperature and pressure |
| the phase diagram of a pure substance shows the regions of pressure and temperature at which | its various phases are thermodynamically stable |
| the liquid-vapour phase boundary terminates at the | critical point |
| at the triple point, solid, liquid, and vapor phases are in | dynamic equilibrium |
| the normal freezing point is the temperature at which the liqiud freezes when the pressure is | 1 atm |
| the normal boiling point is the temperature at which the vapor pressure of the liquid is | 1 atm |
| the standard boiling point is the temperature at which the vapor pressure reaches | 1 bar |
| the critical point is where liquid-vapor equilibrium | ends |
| the critical point is the last point where you can distinguish from liquid and vapor phases because anything above that gives a | supercritical fluid |
| suppose two phases are in equilibrium at a given pressure and temperature. If we change the pressure, we must adjust the temperature to a different value to ensure that | the two phases remain in equilibrium |
| the Clausius-Clapeyron equation relates the temperature dependence of he vapor pressure of a liquid or a solid to | deltaHvap or deltaHsubl |
| for the Clausius-Clapeyron equation we assume that | the vapor behaves as a perfect gas and the enthalpy of vaporization is constant over the temperature range of interest and the molar volume of a gas is much greater than that of a liquid |
| can 4 phases of a single substance ever be in equilibrium | no because F=C-P+2 |
| the number of components in a system is the minimum number of independent species necessary to define the composition of all the phases | present in the system |
| how many components does pure water system have | C=1 |
| how many components does a mixture of ethanol and water have | C=2 |
| the number of degrees of freedom, F, of a system is the number of | intensive variables (ex. pressure, temperature, or mole fractions) that can be changed independently without disturbing the # of phases in equilibrium |
| when F=1 for 2 phases meaning you can vary | one variable, ex. pressure, but the moment you change P, T becomes fixed |
| when the triple point lies above 1 atm the liquid cannot | exist at normal atmospheric pressures whatever the temperature |
| two phases are considered to be in mutual equilibrium when the | temperature, pressure, and chemical potential of each component are the same in each phase |
| consider the ideal gas reaction: PCl5 = PCl3 + Cl2. When He is added at constant temperature & volume in an equilibrium mixture at 25 degrees Celsius, indicate whether the equilibrium shifts to the right, left, or neither | constant T, V addition of He doesn't affect the partial pressures of the gases therefore there is no shift |
| consider the ideal gas reaction: CO + 1/2O2 = CO2 for which deltaHnodR=-283.0 kJ/mol. Predict the change in the partial pressure of CO2 as the temperature is increased at constant total pressure | it will decrease following Le Chatlier's principle because the reaction is exothermic |
| Quantum mechanics can be described as laws governing the behavior of | microscopic particles such as electrons and nuclei |
| quantum mechanics deals with systems that are not part of everyday macroscopic experience, and the formulation of quantum mechanics is math based and | abstract |
| essentially all of chemistry is a consequence of the laws of | quantum mechanics |
| if we want to understand chemistry at the fundamental level of electrons, atoms, and molecules, then we must understand | quantum mechanics |
| after its discovery, quantum mechanics was used to develop concepts that explained chemical properties. However, quantum mechanics was | of little practical value because of the very difficult calculations needed to apply quantum mechanics to chemical systems |
| in present times, the extraordinary computational power of modern computers allows quantum mechanical calculations to give | accurate chemical predictions in many systems of chemical interest |
| the basic constituents of matter are | atoms |
| Newton's Laws apply universally; Newtonian mechanics explained | macroscopic behavior of matter, planetary motion |
| classical mechanics predicts precisely specified locations and | momenta at each instant (deals with the laws of motion of macroscopic objects whose speeds are small compared with the speed of light) |
| in the late 19th century, some people believed that the theoretical structure of physics was | complete and there was nothing else to learn |
| experimental evidence showed up that could not be explained by classical physics and these results led to the development of | quantum theory and the theory of relativity |
| an understanding of atomic structure, chemical bonding and molecular spectroscopy must be based on | quantum theory |
| quantum mechanics describes | the rules that apply to electrons in atoms and molecules |
| quantum mechanics is not deterministic but is | probablistic |
| visible light is one type of electromagnetic | radiation |
| when a solid is heated, it emits light; classical physics pictures light as | wave consisting of oscillating electrical and magnetic fields (electromagnetic wave) |
| electromagnetic waves are synchronized oscillations of | electric and magnetic fields that propagate at the speed of light |
| frequency is the number | of cycles the wave undergoes per second; expressed in s-1 or hertz (Hz) |
| wavelength is the | distance between any point on a wave and the corresponding point on the next crest (trough) of the wave |
| in a vacuum, all types of electromagnetic radiation travel | at 3.00 X10^8 m/s which is a physical constant called the speed of light |
| amplitude of an electromagnetic wave is | a measure of the strength of its electric and magnetic fields |
| amplitude is related to the intensity of | radiation which we preceive as brightness for visible light |
| rotational spectroscopy takes places using what type of waves | microwaves |
| vibrations use infared and visible light which means that | rotational spectroscopy gets super imposed on IR; UV-vis has rotations and vibrations super imposed |
| different solids emit radiation at different rates at different temperature meaning you can associate temperature with a | color scale |
| a blackbody is an idealized object that absorbs all electromagnetic radiation that | falls on it |
| a good approximation of a blackbody is a cavity with a tiny hole because | radiation that enters the hole is repeatedly reflected within the cavity; at each reflection a certain fraction of the radiation is absorbed by the walls of the cavity; large # of reflections causes virtually all radiation to be absorbed |
| when a blackbody is heated the walls emit light equal to what it absorbed because | no light is reflected or transmitted |
| the rate or radiation emitted per unit surface area of a blackbody is a function of | only its temperature and is independent of the material of which the blackbody is made |
| classically blackbody radiation cannot be explained because | radiation from a blackbody is a result of e- oscillating w/ a certain frequency; energies of the electronic oscillators reponsible for the emission of radiation can have any value; well it cannot exactly have any value it wants |
| Rayleigh-Jeans Law is a classical law approximating the intensity of radiation | emitted by a blackbody |
| Rayleigh-Jeans Law had great deviation at | low wavelengths |
| the ultraviolet catastrophe | also called the Rayleigh–Jeans catastrophe, was a prediction of late 19th century/early 20th century classical physics that an ideal black body at thermal equilibrium will emit radiation with infinite power |
| the ultraviolet catastrophe stated that cool objects should | radiate in the visible and UV regions |
| in 1900 Max Planck announced that he had discovered a formula that would give highly accurate fit to the observed curves of the | blackbody radiation |
| Planck considered the walls of the blackbody to contain electric charges that | oscillated (vibrated) at various frequencies |
| it was understood at the time when Planck was working that the origin of blackbody radiation is due to the | vibration of electric dipoles formed by atomic nuclei and their associated electrons which emit radiation at the frequency at which they oxcillate |
| from Maxwell's electromagnetic theory of light, it was known that | electromagnetic waves are produced by accelerated electric charges |
| a charge oscillating with a frequency, v, will emit radiation of | that frequency |
| Planck made a few assumptions: | energy of the oscillator was proportional to an integral multiple of frequency; E=nhv where n=0,1,2,... and h was the proportionality constant |
| Planck made an adjustment to Rayleigh-Jean's Law by plugging in | his equation into theirs |
| Planck showed that his added to Rayleigh-Jean's gave | excellent agreement with the experimental data for all frequencies, wavelengths, and temperatures if h has the value 6.626X10^-34 |
| Planck constant | was found to be 6.626X10^-34 by using his adjustment to Rayleigh-Jean's equation and solving for different frequencies, wavelengths, and temperatures |
| in classical physics, energy takes on a continuous range of values and a system can gain or lose any amount of energy but Planck's ideas | were a direct contradiction to classical physics by saying there were only certain values (it was quantized) |
| the Latin word quantum means | how much |
| in quantum mechanics the energy of a system is | quantized, meaning that the energy can take on only certain values |
| Planck also proved his derivation of the Rayleigh-Jean's Law using the | Wien displacement Law: lambdamaxT = 2.90X10^-3 mK |
| in astronomy the theory of blackbody radiation is used to estimate | the surface temperature of stars |
| in the early 19th century the French scientists Dulong and Petit determined the heat capacities of a number of | monoatomic solids |
| Molar heat capacities of all monoatomic solides are the same and close to | 25 J/K*mol |
| if classical physics were valid, the equipartition principle could be used to infer that the mean energy of an atom | as it oscillates about its mean position in a solid is kT for each direction of placement (for 3 directions of motion) and the derivative was taken and found to equal 25 J/K*mol |
| significant deviations of heat capacities were observed from Dulong and Petit's deviation of molar heat capacities at | low temperatures |
| spectroscopy is the | detection and analysis of the electromagnetic radiation absorbed, emitted, or scattered by a substance |
| Balmer, Rhydber, and others found an empirical formula that correctly reproduces the | observed H-atom spectral frequencies |
| the Rydberg equation and the value of the constant are based on | data rather than theory |
| the Rydberg equation has two sets of integers which can be described as different | series |
| the Lyman series ends at nb = | 1; seen in the UV |
| the Balmer series ends at nb = | 2; seen in the visible |
| the Paschen series ends at nb= | 3; seen near the IR |
| the Bracket series ends at nb = | 4; seen in the IR |
| if intensity is constant e-s begin coming out only at a specific | wavelength |
| if you cross the threshold that e-s begin to emerge | they come out faster (speed increases, KE increases if mass doesn't change) |
| energy is proportional/inversely proportional to wavelength | inversely proportional |
| after you cross the threshold of frequency KE increases and frequency | increases |
| Einstein drew on Planck's idea of | quantized energy |
| work function corresponds to | ionization energy of metals |
| what energy isn't used for work function goes into what when incoming energy equals h(nu) | 1/2 mv^2 |
| nu nod is the threshold frequency where KE= | 0 |
| at KE=0 hv = | work function |
| when alpha particles were shot at metal they deflected as opposed to going right through meaning | they must have hit something at the center of the atom |
| Rutherford's model of the atom led to | Bohr's model |
| Bohr said that the e-s can't just be in any | orbit or they would kill the atom |
| photoelectric effect is that when | photons of sufficiently high energy strike a metal surface, electrons are emitted from the metal |
| experimental characteristics of photoelectric effect | KE of e-s increases w/ frequency but is independent of intensity of the radiation; if frequency is above the threshold e-s are ejected even at low light intensities; no e-s are ejected if the frequency is less than the threshold value |
| the threshold frequency differs for most metals and lies in the | ultraviolet for most metals |
| from the classical picture, the photoelectric effect would expect that the KE of the emitted e-s to | increase with an increase in light intensity and photoelectric effect should occur at any frequency provided the light is sufficiently intense |
| in 1905 Einstein explained the photoelectric effect by extending | Planck's concept of energy quanitzation to electromagnetic radiation |
| Einstein expanded Planck's when extended | Rayleigh-Jean's Law |
| Einstein proposed that in addition to its wavelike properties, light could also be considered | to consist of particle like entities (quanta) |
| Ephoton= | h(nu) |
| work function is | the energy required to remove an electron from the metal to infinity, analogue of ionization energy |
| in 1911 Rutherford proposes nuclear model: atom can be thought of as | a 'microscopic solar system' in which the e-s orbit the nucleus |
| Bohr took Rutherford's idea and said that | the e-s can't just be in any orbit or they would kill the atom |
| classical physics states than an e- in orbit around an atomic nucleus should emit | electromagnetic radiation (photons) continuously, b/c it's continually accelerating in a curved path; the resulting loss of energy implies that the e- should spiral into the nucleus...(aka atoms can't exist) |
| Bohr postulates | H has only certain stationary states, atom doesn't radiate energy while in a stationary state; going from a higher to lower level releases a photon; e- in stationary state moves in a circle around nucleus; allowed orbits follow e-s angular momentum |
| Bohr called energy levels | stationary states |
| the force holding the e- in a circular orbit, according to Bohr, is | the coulombic force of attraction between the proton and the e- |
| Bohr balanced the coulombic force with the | centrifugal force (b/c moving in an orbit) |
| n=1 corresponds to the state of | lowest energy; ground state energy |
| negative sign indicates that the energy states are | bound states; i.e. the energies given by the Bohr orbits radius equation are less than when the p+ and e- are infinitely apart (n=infinity) |
| n>1 is also called an | excited state |
| at ordinary temperatures hydrogen atoms, as well as most other atoms and molecules, are found exclusively in the | ground electronic states |
| state of higher energy are called excited states and an atom or molecule in that state will relax back to the ground state and give off | energy in the form of a photon |
| Bohr's equation had good agreement with the experimental value of the | Rydberg constant |
| ionization energy is the energy required to | take an e- from the ground state to the first unbound state, which is obtained by letting nb=1 and na=infinit |
| limitations of ionization energy, Bohr's model, and Rydberg's equation | failed to predict the spectrum of any other atom other than hydrogen |
| Bohr model is a one-electron model and works for | He+, Li2+, and Be3+ |
| wave particle duality is an extension of the | Bohr theory to explain the spectra of atoms when more than one e- failed; the fact that Bohr theory works for hydrogen is somewhat of an accident |
| de Broglie proposal (1923) | if light can be particle-like at times, why should matter not be wave-like at times |
| quantization occurs in wave motion such as seen in sound waves; when a string is plucked it can vibrate at its fundamental frequency with overtones being n(nu) where n is an | integer; frequencies lying between these mulitplies of nu are not allowed |
| de Broglie proposed that a material particle with a momentum would have a wavelength lambda given by | lambda = h/p where p=mv momentum |
| does de Broglie's relationship of lambda = h/p apply to all particles | yuppers; ex. baseball; e-; the difference is the degree by which it matters to the object |
| Davisson and Germer experiment | scattering of e- beam from the nickel crystal shows a pattern characteristic of a diffraction experiment where waves interfere constructively & destructively in different regions |
| classical experiments had shown matter to be particle-like and energy to be wave-like, but de Broglie, Davisson, and Germer showed that the distinction between a particle and a wave is meaningful only in | the macroscopic world, not the atomic world; aka wave-particle duality |
| Heisenberg Uncertainty Principle states that | the more precise you know the position the less precise you known the momentum and vice versa |
| in the classical view of the world a moving particle has a definite location at any instant whereas a wave is spread out in space but an e- has the properties of | both a wave and a particle |
| uncertainty in the linear momentum parallel to the axis q and deltaq is the uncertainty in the position along | that axis |
| the basic approach of microscopy is illuminating a small area of a sample and collecting light with a | microscope |
| the resolution of a microscope is on the order of | wavelength of light used as a probe |
| conventional microscopes that use visible light are | blind to features in the nanometer range |
| the wavelength of light is an important factor in the resolution of a microscope. The greatest resolving power in optical microscopy is near the | UV light, the shortest effective imaging wavelength |
| under most circumstances microscopists use white light generated by tungsten-halogen bulb to illuminate | the specimen |
| in electron microscopy a beam of e- w/ a well-defined de Broglie wavelength (wave particle duality) replaces the lamp found in traditional light microscopes and instead of glass or quartz lenses, | magnetic fields are used to focus the beam |
| because of the Broglie wavelength, microscopes have the best resolving power at low | wavelengths |
| in transmission electron microscopy, TEM, the e- beam | passes through the specimen and the image is collected on a screen; more resolution than SEM but can't be done on every sample; needs a super thin slice w/ an e- beam shining through) |
| in scanning electron microscopy, SEM, the e-s scattered back are | detected & the electrical signal is sent to a video screen; an image is obtained by scanning the e- beam across the surface of the sample (3D view) |
| typical resolutions of TEM and SEM instruments are about | 2 nm and 50 nm respectivevly; it follows that e- microscopes cannot resolve individual atoms (which have diameters of about 0.2 nm) |
| for e- microscopes only certain samples | can be observed under certain conditions |
| for e-microscopes the measurements must be conducted under | high vacuum b/c air molecules can cause difraction |
| for TEM observations the samples must be very | thin cross-sections of a specimen (hard to make); cannot be used to study living cells |
| for SEM observations the samples must be | made on dry samples; cannot be used to study living cells |
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