課程名稱︰普通化學丙
課程性質︰系訂必修
課程教師︰彭旭明
開課系所︰醫學系
考試時間︰2005.1.25
試題 :
(1)Dinitrogen oxide, N2O, gas was generated from the thermal decomposition of
ammonium nitrate and collected over water. The wet gas occupied 126 mL at
21 ℃ when the atmospheric pressure was 755 Torr. (a) What volume would the
same amount of dry dinitrogen oxide have occupied if collected at 755 Torr
and 21 ℃ ? The vapor pressure of water is 18.65 Torr at 21 ℃.(4%) (b)
Write down the chemical equation. (2%)
(2)A bottle contains 1.0 mol He(g) and a second bottle contains 1.0 mol Ar(g)
at the same temperature. At that temperature, the root mean square speed of
He is 1477 m*s^-1 and that of Ar is 467 m*s^-1. What is the ratio of the
number of He atoms in the first bottle to the number of Ar atoms in the
second bottle having these speed? Assume that both gases behave ideally.(6%)
★Root mean square: √<v^2> = √(3RT)/M
★Maxwell distribution of speeds: f(v)=4π(M/2πRT)^1.5*v^2*e^(-Mv^2/2RT)
(3)A graduate student needs to prepare isotopiacally labeled phosgene gas,
13COCl2(g) (註:含C-13的2氯甲醛), for use in the synthesis of an organic
compound (all the C atom are carbon-13). The student places 3.59 atm of
13CO(g) and 2.75 atm of Cl2(g) in a steel cylinder at 25℃, seals the
cylinder, and heats it to 227℃. After the cylinder is kept at the elevated
temperature for a week, the pressure inside the cylinder is found to be 9.75
atm while still at 227℃.(a)What are the mole fractions of 13CO, Cl2, and
13COCl2 present in the vessel at the end of the week?(b)What is the density
of the mixture?(c)If it is in an equilibrium, what is the equilibrium
constant Kp?(9%)
(4)A 1.00-L sample of chlorine gas at 1.00 atm and 298 K reacts completely with
1.00L of nitrogen gas and 2.00L oxygen at the same temperature and pressure.
There is a single gaseous product, which fills a 2.00-L flask at 1.00 atm
and 298K. Use this information to determine the following characteristics of
the product: (a)its empirical formula; (b)its molecular formula; (c)the most
favorable Lewis structure based on formal charge argumanets(the central atom
is an N atom); (d)the molecular shape.(8%)
(5)Two samples of gas are seperated in two rectangular 1.00-L chambers by a
thin metal wall. One sample is pure helium and the other is pure radon. Both
samples are at 27℃ and show a pressure of 2.00*10^-6 atm. Assuming that the
metal wall seperating the gases suddenly develops a circular hole of radius
1.00*10^-6 m, calculate the pressure in each chamber after 10.0 hour have
passed.(10%)
★ Collision rate: Za = a*N/V*√(RT/2πM)
★ Atomic weights: He = 4.00 Rn = 222
(6)What percentage of space is occupied by close-packed cylinders of length l
and radius r ?(4%)
(7)(a)Calculate the number of cations, anions, and formula units per unit cell
in the fluorite (CaF2) unit cell shown here.(b)What are the coordination
numbers of the ions in fluorite?(c)Give the fractional coordinate of the
ions in unit cell in fluorite.(7%)
那個圖是說
八個頂點上和每個面上是鈣離子
八個氟離子被鈣離子以四面體型夾在中間
(8)Metals with bcc structures, such as tungsten, are not close packed.
Therefore, their densities would be greater if they were to change to a ccp
structure(under pressure, for instance). What would the density of tungsten
be if its structure were ccp rather than bcc? Its actual density is
19.3 g*cm^-3.(4%)
(9)Are the following statements true or false? (a)If there is an atom present
at the corner of a unit cell, there must be the same type of atom at all the
corners of the unit cell.(b)A unit cell must be defined so that there are
atoms at the corners.(c)If one face of a unit cell has an atom in its center
, then the face opposite that face must also have an atom at its center.(d)
If one face of a unit cell has an atom in its center, all the faces of the
unit cell must also have atoms at their centers.(4%)
(10)A sample of gas in a cylinder of volume 3.42 L at 298 K and 2.57 atm
expands to 7.39 L by two different pathways. Path A is an isothermal,
reversible expansion. Path B has two steps. In the first step, the gas is
cooled at constant volume to 1.19 atm. In the second step, the gas is
heated and allowed to expand against a constant external pressure of 1.19
atm until the final volume is 7.39 L. Calculate the work for each path.
(11)The high-temperature contribution of vibrational modes to the molar heat
capacity of a solid at constant volume is R for each mode of vibrational
motion. Hence, for an atomic solid, the molar heat capacity at constant
volume is approximately 3R.(a)The specific heat capacity of a certain
atomic solid is 0.392 J*K^-1*g^-1. The chloride of this element (XCl2) is
52.7% chlorine by mass. Identify the element. (b)This element crystallizes
in a faced-centered cubic unit cell and its atomic radius is 128 pm. What
is the density of this atomic solid?(8%)
★ R =8.314 J*K^-1*mol^-1 ★ Atomic weights: Cl = 35.45
(12)(a)Calculate the work associated with the isothermal, reversible expansion
of 1.000 mol of an ideal gas from 7.00 L to 15.50 L at 25.0℃. (b)Calculate
the work associated with the irreversible adiabatic expansion of the sample
of gas described in part(a) against a constant atmospheric pressure of 760
Torr. (c)How will the temperature of the gas in part(b) compare with that
in part(a) after the expansion?(8%)
(13)Robert Curl, Richard Smalley, and Harold Kroto were awarded the Nobel prize
in chemistry in 1996 for the discovery of the soccer-ball-shaped molecule
C60. This fundamental molecule was the first of a new series of molecular
allotropes of carbon. The enthalpy of combustion of C60 is -25937 kJ*mol^-1
, and its enthalpy of sublimation is +233 kJ*mol^-1. There are 90 bonds in
C60, of which 60 are single bonds and 30 are double bonds. Like benzene,C60
has a set of mutiple bonds for which resonance structures may be drawn.(a)
Determine the enthalpy of formation of C60 from its enthalpy of combustion.
(b)Calculate the expected enthalpy of formation of C60 from bond enthalpies
, assuming the bonds to be isolated double and single bonds.(c)Is C60 more
or less stable than predicted on the basis of the isolated-bond model?(d)
Quantify the answer to part(c) by dividing the difference between the
enthalpy of formation calculated from the combustion data and that obtained
from the bond enthalpy calculation by 60 to obtain a per carbon value.(e)
How does the number in part(d) compare with the per carbon resonance
stabilization energy of bezene(the total resonance stabilization enerdy of
bezene is approximately 150kJ*mol^-1)?(f)Why might these values differ?(10%
)
★ The enthalpy of atomization of C(gr) is +717 kJ*mol^-1
★ΔHf°(CO2) = -393.51 kJ*mol^-1
★Mean bond enthalpy : C-C 348 kJ*mol^-1
C=C 612 kJ*mol^-1
(14)List the following substances in order of increasing molar entropy at 298K:
H2O(l), H2O(s), C(s, diamond), H2O(g). Explain your reasoning.(4%)
(15)Initially a sample of ideal gas at 323K occupies 1.67 L at 4.95 atm. The
gas is allowed to expand to 7.33L by two pathways: (a)isothermal,
reversible expansion; (b)isothermal, irreversible free expansion. Calculate
ΔStot, ΔS and ΔSsurr for each pathway.(8%)
(16)Assuming statistical disorder, would you expect a crystal of octahedral
cis-MX2Y4 to have the same, higher, or lower residual entropy than the
corresponding trans isomer? Explain your conclusion.(4%)
(17)The three compounds methylpropene, cis-2-butane, and trans-2-butane are
isomers with formula C4H8, with ΔGf°= +58.07, +65.86, and+62.97 kJ*mol^-1
, respectively. In the presence of a suitable metal catalyst, these three
compounds can be interconverted to give an equilibrium gaseous mixture.
What will be the percentage of each isomer present at 25 ℃ once
equilibrium is established?(10%)
★ ΔG°= -RTlnK
(18)Prove that the heat spontaneously folws from high temperature substance to
low temperature substance, i.e. the processis increasing in entropy.(8%)
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