Exam (elaborations)
CEM 141 - Cumulative Final (1)
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- Chemistry 141
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- Chemistry 141
CEM 141 - Cumulative Final (1)
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CEM 141 - Cumulative FinalIt is impossible to predict from the information provided because the color of the product does
not depend on the color of the reactant(s) since the properties of the product are emergent. -
ANS-A compound that is red in color reacts with a compound that is yellow in color to make a
product. At room temp, what color will the product be and why?
Orange; Red; Yellow It is impossible to predict from the information provided
Because: the color of the product is the same as the color of the reactant; the color of the
product does not depend on the color of the reactant(s) since the properties of the product are
emergent; the color of the products will be a mixture of the colors of the reactants
Energy is absorbed into the system and interactions between the molecules are overcome. -
ANS-What happens to the system when a molecular substance (such as H2) boils?
3 - ANS-Figure A is an incomplete molecular orbital diagram. Complete the diagram for the
imaginary diatomic molecule X2, where each atom of X has 5 valence electrons in s and p
orbitals. Based on your diagram, how many bonds does this molecule have?
When a photon of light is absorbed in a piece of metal, an electron is promoted to a higher
energy molecular orbital within the band. When the electron drops back into the lower energy
level, a photon is emitted. - ANS-Why are metals shiny?
The melting point of C is higher than that of C60 because the covalent bonds in C are stronger
and require more energy to overcome than the LDFs between C60 molecules. - ANS-Make a
prediction about the relative melting points of diamond, C, and the molecule
buckminsterfullerene, C60, then choose the statement that best explains your prediction.
The melting point of C is lower than that of C60; The melting point of C is higher than that of
C60; The melting point of C is the same as that of C60
Because: C has a lower molar mass than C60, so the LDFs between particles will be weaker
and require less energy to overcome; C and C60 are both pure carbon, so they have identical
properties; The covalent bonds in C are stronger and require more energy to overcome than the
LDFs between C60 molecules; There are fewer covalent bonds in C than in C60, which require
less energy to overcome
Three sp2 hybrid orbitals on each atom overlap end-to-end while the unhybridized p-orbitals
overlap side-to-side. - ANS-According to Valence Bond Theory, how do bonds form between
carbon atoms in graphite?
1 and 3 - ANS-The Lewis structure for neopentane is shown in Figure B. Which of the other
structures below it are appropriate representations for neopentane?
+1 - ANS-What is the formal charge on the N in the structure on Figure C?
, Two single bonds and two lone pair of electrons. - ANS-Draw the Lewis structure for a molecule
of SF2. How many bonds and lone pair of electrons are on the central atom, S?
Same molecule because these compounds have the same molecular formula and the atoms are
connected in the same way. - ANS-Do the structures in Figure D represent the same molecule,
isomers, or neither? Why?
Because: these compounds have different formulas; these compounds have the same
molecular formula and the atoms are connected in the same way; the compounds have different
molecular formulas and the atoms are connected in a different way
Yes, it is easy to rotate around that bond because the overlap between the hybrid orbitals
involved in the bond doesn't change upon rotation. - ANS-Consider the bond indicated by the
arrow in Figure D. Is it easy to rotate around that bond and why or why not?
Trigonal Pyramidal - ANS-Refer to the Lewis structure on Figure E. What is the shape around
atom Z?
sp2 - ANS-Refer to the Lewis structure on Figure F. What is the hybridization of atomic orbitals
on atom C2?
Sulfur because it has a higher effective nuclear charge. - ANS-Which is more electronegative
and why?
Phosphorus or Sulfur
Because: It has a higher effective nuclear charge; It has a lower effective nuclear charge; It is
further right on the periodic table; It is further left on the periodic table
Nonpolar because the bonds between B and Cl are polar and the molecular shape of BCl3 is
trigonal planar, therefore the bond dipoles will cancel out - ANS-Is boron trichloride (BCl3) polar
or nonpolar and why? (Hint: Lewis structure)
Because: The bonds between B and Cl are polar; The bonds between B and Cl are nonpolar;
The molecular shape of BCl3 is trigonal pyramidal, therefore the bond dipoles will not cancel
completely, resulting in a molecular dipole; The molecular shape of BCl3 is trigonal planar,
therefore the bond dipoles will cancel out
Dipole-Dipole interactions - ANS-What is the strongest type of intermolecular force that can exist
between the two molecules in Figure G?
3 and 5 - ANS-See figure H. Which of the numbered bonds are hydrogen bonding interactions?
Butane contains a larger electron cloud. Because butane is more polarizable, the molecules
have larger instantaneous dipoles and stronger London Dispersion Forces, requiring more
energy to overcome. - ANS-Select the evidence and reasoning for the following claim.
Claim: Butane (CH3CH2CH2CH3) has a higher boiling point than ethane (CH3CH3).
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