65 . C
The molecular weight of sodium nitrite is 69 grams/mole. Since there is one nitrogen atom per
formula unit, we can find the weight fraction of sodium nitrite that is nitrogen by dividing the
atomic weight of nitrogen, 14 grams/mole, by the molecular weight of sodium nitrite, 69
grams/mole. If we multiply this fraction, 14/69, by 50 grams, we get 10.1 grams.66 . D
This question asks you to predict which combination of ∆H and T∆S values will always give a
spontaneous reaction. Recall that spontaneous reactions have negative values of Gibbs free
energy, ∆G, and that ∆G = ∆H − T∆S , where ∆H is the change in enthalpy, ∆S is the change in
entropy, and T is the absolute temperature. This is the key equation, which you probably have
memorized. From this equation, it’s clear that the best way to guarantee a negative ∆G is to
have a negative ∆H value and a positive ∆S value since T, in Kelvin, is always positive.
67 . C
The most nonmetallic compound is Si; these elements are found in the right-hand corner of
the periodic table. The most metallic (it actually is a metal) is Pb; these elements are found on
the left-hand side of the periodic table and through all the transition metals. Also, in Groups III
through VII, nonmetallic character increases as you go up the periodic table. Therefore, the
order of these elements in decreasing nonmetallic character would be Si, Ge, Sn, Pb.
68 . C
Group IA elements are alkali metals; they have low densities, large atomic radii, low ionization
energies, and low electronegativities. They are metals and have metallic bonding, and are
good conductors of electricity. However, they have low melting points.
69 . A
This question boils down to definitions. The electron affinity of an atom is defined as the
change in energy that occurs when an electron is added to a gaseous neutral atom in its
ground state. So electron affinities can be positive or negative, depending on whether energy
is released when an atom spontaneously accepts an electron or energy is gained when an
electron is forced onto an atom. So choice A is the correct answer. Electronegativity is a
derived quantity, usually scaled for all atoms between 0 and 4, that characterizes the pull an
atom has for the electrons in a bond. The electronegativity has nothing to do with how likely
an atom is to gain an electron, just how strong its pull is on an electron in a bond. The “in a
bond” part is very important. The concept of electronegativity can only be applied to atoms