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School of Science and Engineering (SSE)
Spring 2017
General Chemistry II (CHE 1402)
Homework 2
(Chapter 12: Intermolecular forces)
All number should be reported to the proper significant figures
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Avogadro Number = 6.023×1023 ; Gas constant R= 0.082 L.atm/K-mol or R= 8.314 J/K-mol
I
1) Based on the figure below, what is the boiling point of diethyl ether under an external
pressure of 1.32 atm?
2) Elements A and B have identical densities and unit cell volumes for their crystalline
lattice. Element A crystallizes in a body-centered cubic lattice and element B crystallizes
in a face-centered cubic lattice. What can be concluded concerning the molar mass of A
and B?
II
1. Explain why the orders of the boiling points of the compounds, shown in the following
graph, are as follows:
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HF (19.5 °C) > HI (-35.4 °C) > HBr (-66.8 °C) > HCl (-.85 °C)
H2O (100 °C) > H2Te (-1.0 °C) > H2Se (-42.0 °C) > H2S (-60.7 °C)
BiH3 (16.88 °C > SbH3 (-17.0 °C) > NH3 (-33.4 °C) > AsH3 (-63.0 °C) > PH3 (-87.7 °C)
2. Indicate the main type of intermolecular forces that operates in each of the following
substances: IF, BF3, NF3, XeF4.
III
1. Place the following substances in order of decreasing volatility assuming that their
polarities are similar: CH4, CBr4, CH2Cl2, CH3Cl, CHBr3, CH2Br2
2. What are the major attractive forces that exist in each of the following molecules.
CO2, H2, IF, BF3, and CCl4
IV
Ethanol, C2H5OH, melts at –114°C and boils at 78 °C. The enthalpy of fusion of ethanol
is 5.02 KJ/mol, and its enthalpy of vaporization is 38.56 KJ/mol. The specific heats of
solid and liquid ethanol are 0.97 J/g-K and 2.3 J/ g-K respectively.
What is the enthalpy change required to convert 10.0 g of ethanol at –150 °C to the vapor
at 78°C
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V
1. The phase diagram of a substance is given above. What is the physical state of this
substance at 25°C and 1.05 atm.
2. Shown here is a portion of the phase diagrams for H2O and CO2.
a. Explain why the melting curve of H2O deviates to the left and that of CO2 deviates to
the right.
b. A sample of CO2 cannot be melted by heating it in a container open to the
atmosphere. Explain why this is so.
c. The critical temperature and pressure of H2O are 374°C and 218 atm, respectively. At
critical pressure and temperatures above 374°C, what is the physical state H2O?
VI
1. What fraction of the volume of each corner atom is actually within the volume of, a
primitive cubic, body centered cubic, and a face-centered cubic unit cells, ?
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2. At room temperature copper (Cu) crystallizes in a face-centered cubic unit cell that has
an edge length of 3.61 A° Assuming that atoms touch along the diagonal of the face of
the unit cell, determine the density and radius of copper metal (MCu=63.5 g/mol).
3. Determine the percentage of empty space in the unit cell.
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