CHEM 3492 Study Guide - Midterm Guide: Path Dependence, Laboratori Nazionali Del Gran Sasso, Isothermal Process

Could you please answer these questions

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Practice problems for exam 2 ______________

Useful Information:

h=6.626×10-34J·s.; c=3.0×108 m/sec; E=h ; E= hc ,  = h/mv; 1J = 1 kg-m2/s2 

mass of electron = 9.11 × 10-28 g, E= q + w ; 1 cal = 4.184 Joules Please Show all Work

1. Which of the following substances have standard heats of formation that are equal to zero by definition (circle your answers): H2(g), H(g), O3(g), H2O(s), H2O(l), Hg(l), Hg(s), Hg(g).

2. Limestone stalactites are formed in the reaction: Ca2+(aq) + HCO3-(aq) ïƒ CaCO3(s) + CO2(g) +

H2O(l)
If one mole of CaCO3 is produced at 298 K under one atmosphere of pressure, the reaction performs 590 calories of expansion work, pushing back the atmosphere as CO2 is formed. At the same time, 9310 calories of heat are absorbed from the environment. What is E in Kcal/mole for CaCO3.

3. What is the minimum wavelength of light in Å (1 Å = 10-8 cm) needed to provide enough energy per quantum to rupture the chemical bond in hydrogen iodide (HI). The bond dissociation energy of HI is 71.4 Kcal/mole.

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4. Sketch the shape and orientation of the following types of orbitals: s, px, dxy, dz2, dx2-y2

5. Give the values of (n) , (l) and (ml) for each orbital in the 4p subshell.

6. Write the complete electron configuration for the following: Ti 2+_____________________________________ Cr_______________________________________

N______________________________________

7. Calculate the standard enthalpy of formation (  Ho) for diamond from graphite [i.e. C (graphite) ïƒ C (diamond)] given that:

C (graphite) + O2 ïƒ CO2 (g) (  Ho = -393.5 KJ/mole) C (diamond)] + O2 ïƒ CO2 (g) (  Ho = -395.4 KJ/mole)

If 1.0g of graphite is converted to diamond, what is the energy change? Is this an endothermic or exothermic reaction?

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8. An 160 pound astronaut on his way to Mars is buzzing along at 10,000 miles per hour. (a) Express his weight in grams (one pound = 454 grams) so that you can calculate the astronaut’s wavelength (1mile/hour = 44.7 cm/sec)

(b) Suppose the astronaut detects outside his spacecraft a proton (m=1.7 x 10-24 g) from a “solar wind” moving at exactly the spacecraft velocity. What is the proton wavelength is in Å (1 Å = 10-8 cm.

9. What is the maximum number of electrons that can occupy each of the following subshells? a) 3d_________________ b) 1s____________________ c) 2p ____________________

10. Identify the element represented by the following electronic configuration.

a) [Ne] 3s2____________________

b) What is the electron configuration for the first excited state of this atom.______________

11. Determine the number of valence electrons for each element.
(a) Br___________ (b) Na _________ (c) Sn __________

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12. 175 g of Fe at 15.0oC is mixed with 225 g of H2O at 95.0oC. What is the final temperature of the mixture? The specific heats of iron= 0.448 J/g oC and water = 4.184 J/g oC). (keep in mind the following: heat gained + heat lost = 0 and q=mass x heat capacity x T)

13. (5 pts) Calculate values of ΔHrxn for the following reactions: CS2(g) + 3O2(g)  CO2(g) + 2SO2(g)

The heat of formation for the following substances is given in kJ/mol:

CS2 CO2 SO2 117.4 -393.51 -296.83

14. (6 pts) Use the electron configuration of Li and Be and determine which element has the greatest second ionization energy. Defend your answer.

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15. Mark beside each of the following processes either “exo” or “endo” according to whether you think the process will release heat or absorb heat.

a. Ca(g) ïƒ Ca(g)+2 + 2e-
b. I(g)+1e-ïƒ I(g)-1
c. Ca(g)+2 + S(g)-2 ïƒ CaS(s) d. I2(g)ïƒ 2I(g)

( ) ( ) ( ) ( )

16. (6 pts) In each of the following pairs, which of the two species is larger?
a) O-2 or Na+ b) Ti+4 or Ti+2 c) B or C d) N or N-3

17. Write down the Lewis dot structure for the following (a) N_______________ (b) Ne________________

18. THE BORN HABER CYCLE: I may have a problem on the Born Haber cycle. Please check my lecture notes to see how to set up the process and then calculate the lattice energy from the various thermodynamic quantities such as in the NaCl example below;

 H  f NaCl = -411KJ

Na(s)  Na(g)  H =108KJ
1⁄2 Cl2  Cl(g)  H = 122KJ Ionization Energy of Na  H = 496 KJ Electron affinity of Cl  H = -349KJ

For which system below would quantum effects be leastnoticeable?

-The collision of two N₂ molecules in a gas, whichchanges the rotational energy of both

-Polarization of the electron density of ethanol resulting inexcitation of vibrational motions

-An electron-sized particle moving in a 1 m³ box asthe temperature decreases by 10 degrees

-A hydrogen atom being struck by a UV photon

We have dealt with two different ensembles, canonical andmicrocanonical. Which of the following statements is inaccurateregarding these ensembles?

-The canonical ensemble is always considered as a subset of alarger reservoir, which acts as the surroundings.

-The microcanonical ensemble is defined to have constant energy,volume, and composition.

-The microcanonical ensemble is a smaller subset of microstatesof the canonical ensemble.

-The canonical ensemble is generally more useful than themicrocanonical for chemical processes.

Which statement below is most correct regarding the partitionfunction of an ensemble?

-For a given temperature, the high-energy contributions to thepartition function are more heavily weighted.

-Once a partition function is defined in a specific ensemble, itis valid in all other ensembles.

-It tells us the numerical order of the energy levels for agiven system.

-It provides a measure of the energy levels available to asystem at a given temperature.

Consider a cup-carrier from your favorite take-out restaurant.The carrier can hold four cups, and you have to place two cups (onelarge, one small) into the carrier, with no preference forposition. How many microstates can you form with two cups in thefour spaces?

-12

-8

-16

-6

Boltzmann's definition of the entropy was a breakthrough inunderstanding statistical thermodynamics. What is the bestdefinition of Boltzmann's entropy?

-The Boltzmann entropy is a count of the total distinctmicrostates in a system.

-The Boltzmann entropy is a measure of the randomness of anensemble.

-The Boltzmann entropy is a count of the accessible energylevels at a given temperature.

-The Boltzmann entropy is a measure of the useful work availablein an ensemble.

Our canonical ensemble was defined such that the temperature,volume, and number of particles were each held constant. In termsof the Legendre transform, which thermodynamic potential isfundamental in the canonical ensemble?

-The Helmholtz energy

-The internal energy

-The Gibbs energy

-The enthalpy

The equipartition principle can be used to estimate the constantvolume heat capacities of gases. Under which circumstances wouldthe full equipartition heat capacity most closelyapproximate the measured value of C_V?

-A sample of N₂ gas at 373K

-A sample of propane gas (C₃H₈) at roomtemperature

-A sample of water vapor at 373K

-A sample of Br₂ vapor at room temperature

Which factor below does not contribute to the rotationalpartition function of a molecule?

-The rotational quantum number

-The nuclear and electronic spin states

-The rotational constant(s)

-The temperature of the molecule

We were able to reduce the vibrational partition function froman infinite series to a function of a single exponential, but onlyapproximately. Which approximation below was NOT used?

-We assumed that the vibrational energy can be expressed asv?_e.

-We assumed that the energy levels were close enough to allowintegration instead of summation.

-We assumed that the vibrational motion is purely harmonic.

-We assumed that the separations are relatively small, due tohigh temperature or lower vibrational constant.

The derived partition function for an ideal gas depends on allof the physical parameters listed below except for which one?

-Molecular symmetry

-The temperature of the molecules

-The volume of the sample

-Mass of the molecules

Deriving the translational partition function is more involvedthan deriving the rotational and vibrational partition functions.Which statement below is NOT a reason for this?

-There are so many possible translational energy levels, thatthe integral does not converge to a finite value.

-The integral of translational states for a single particle mustbe taken over a 6-dimensional hypervolume.

-The degeneracy of translational states is not obvious becausethey lie so close in energy.

-Translational degrees of freedom involve interactions betweenall molecules in the sample, whereas rotations and vibrations donot.

The connection between the Equipartition Principle and thetranslational partition functions helped to demonstrate that thetemperature of a system depends on the easily excited degrees offreedom. Why should this be true?

-In systems with easily excited degrees of freedom, a change inthe entropy requires energy changes on the order of thermalenergy.

-In systems with easily excited degrees of freedom, smallincreases in the pressure make excited states more accessible,

increasing the temperature.

-In systems with easily excited degrees of freedom, thepotential energy is no longer dependent on the temperature of thesystem.

-In systems with easily excited degrees of freedom, thermalenergy is sufficient to allow one to treat the energy levels as acontinuum.

The connection between the Maxwell-Boltzmann distribution andthe translational partition function allowed us to betterunderstand the distribution of speeds. Which statement below is NOTa consequence of the translational partition function?

-The population of the lowest speeds is very small.

-The pressure of the gas increases as the velocityincreases.

-An increase in the temperature will result in shifting thedistribution to higher energies.

-The population of the highest speeds is very small.

When dealing with quantum energy levels, there are severalimportant factors to consider. Which concept below is NOT importantto quantum energy levels?

-The set of quantum numbers

-Degeneracy

-The deBroglie wavelength

-The ground state