# Gen Chem I Exam # 3

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According to Charles's law, for a fixed quantity of gas at constant pressure, which of the given quantities is constant?
V/T = constant
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Who's law is this? volume of fixed amount of gas at constant pressure is directly proportional to its ABSOLUTE temperature
Charles's law V1/T1 = V2/T2
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Refrigerators are usually kept at about 5βC, while room temperature is about 20βC. If you were to take an "empty" sealed 2-liter soda bottle at room temperature and place it in the fridge, would you expect it to contract to one-fourth its original volume? 1. Yes, because 5 is one-fourth of 20. 2. No, because there is no gas inside the bottle. 3. No, because Celsius is not an absolute temperature scale.
No, because Celsius is not an absolute temperature scale. Note that 20βC=293K and 5βC=278K . So the absolute temperature has not decreased by very much at all, certainly not by a factor of 4. Therefore, the change in size of the plastic bottle would not be very noticeable.
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Avogadro's Law states that at a given temperature and pressure, what quantity is constant?
V/n Since V and n are directly proportional, the quantity V/n will always have the same value at a given pressure and temperature.
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Who's law is this? volume of gas at constant temperature and pressure is directly proportional to the # of moles of the gas
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Which of the following statements are true? Check all that apply. -The average speed of gas molecules decreases with decreasing temperature. -The temperature of a gas sample is independent of the average kinetic energy. -All the gas molecules in a sample cannot have the same kinetic energy. -There are gas molecules that move faster than the average. -The average kinetic energy of gas molecules increases with increasing temperature
-The average speed of gas molecules decreases with decreasing temperature. -All the gas molecules in a sample cannot have the same kinetic energy. -There are gas molecules that move faster than the average. -The average kinetic energy of gas molecules increase with increasing temperature.
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Which statements about a sample of gas containing molecules of different masses are true?
More massive gas molecules in the sample have lower rms speed than less massive ones. The average kinetic energy depends only on the temperature. However, a heavier molecule will move more slowly than a lighter molecule if both have the same kinetic energy.
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Lewis structures vs Valence Shell Electron Pair Repulsion model (VSEPR)
lewis --> shows bonding and lone (nonbonding) pairs, but do NOT denote shape (they can help to determine shapes) VSEPR --> shows bonding and lone (nonbonding) pairs, but DO determine shape of molecule
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what is an electron domain?
the direction to which electrons point In this example, the central atom(A) has 4 electron domains
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For the VSEPR model, "the best arrangement of a given # of electron domains is the one that ________ the repulsions among them."
minimizes
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nonbonding/lone pair size vs. bonding pair size
nonbonding pairs --> physically LARGER causing their repulsions to be greater and compress bond angles
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double and triple bond electron domains vs. single bond electron domains
double and triple bonds have LARGER electron domains and exert a greater repulsive force --> making bond angles greater
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what is the bond angle of H2O?
104.5 (NOT 90) tetrahedral, bent sp3 hybridization
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which electron domains can break the octet rule and have more than 4 bonds?
trigonal bipyramidal (5) octahedral (6)
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Trigonal bipyramidal can have 2 distinct positions in their geometry. What are they?
1. axial 2. equatorial (lone pairs occupy equatorial positions)
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All positions are equivalent in the octahedral domain. T/F?
true
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For larger molecules, look at the geometry about each atom rather than the molecule as a whole. T/F?
true
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the sharing of space b/t 2 electrons of opposite spin in the valence-bond theory results in what kind of bond?
covalent bond *also know that --> the overlap of orbitals is when electrons of 2 atoms begin to occupy the same space
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_______ form by mixing of atomic orbitals to create new orbitals of EQUAL energy called _____ ______
hybrid orbitals degenerate orbitals
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mixing of the s and p orbitals yields what?
2 degenerate orbitals that are hybrids of the 2 orbitals and align themselves 180deg. from each other *sp orbitals have 2 lobes that look like a p orbital *1 of the lobes is larger and more rounded, as is the s orbital
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what is a hypervalent molecule?
elements that have MORE than an octet
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how does a double or triple bond form?
it CANT if we only use hybridized orbitals. If you use orbitals that are NOT hybridized there is a "side-ways" overlap
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sigma and pi bonds are ______ bonds.
covalent bonds
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-head to head overlap -cylindrical symmetry of electron density about internuclear axis - always single a single bond* -strongest form of covalent bonds Is this describing a sigma or pi bond?
sigma bond
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- side to side overlap -electron density above and below internuclear axis Is this describing a sigma or pi bond?
pi bond *multiple bonds have 1 sigma bond, all other bonds are pi bonds
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_______ - bonding electrons (sigma or pi) that are specifically shared b/t 2 atoms
localized electrons vs. delocalized electrons - unable to describe all electrons as localized due to resonance
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molecular orbitals have what similarities to atomic orbitals?
1. maximum of 2 electrons per orbital 2. electrons in same orbital have OPPOSITE spin 3. definite energy of orbital 4. can visualize electron density by a contour diagram
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molecular orbitals have what differences to atomic orbitals?
-molecular orbitals represent entire molecule, not a single atom -whenever 2 atomic orbitals overlap, 2 molecular orbitals are formed --> 1 bonding, 1 anti bonding
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_______ - constructive combinations of atomic orbitals
bonding orbitals
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_______ - destructive combinations of atomic orbitals
anti bonding orbitals *a nodal plane occurs where electron density equals 0
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1. a single bond has how many sigma and pi bonds? 2. a double bond has how many sigma and pi bonds? 3. a triple bond has how many sigma and pi bonds?
1. single = 0 pi, 1 sigma 2. double = 1 pi, 1 sigma 3. triple = 2 pi, 1 sigma
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what is a chemical bond is in terms of electron density between 2 atoms?
a concentration of electron density b/t nuclei of 2 atoms. this concentration takes place b/c orbitals on the 2 atoms overlap
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What is meant by the term orbital overlap?
this occurs when a valence atomic orbital on 1 atom shares the same space with a valence atomic orbital on an adjacent atom
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What is the difference between hybrid orbitals and molecular orbitals?
-hybrid orbitals are mixtures (linear combinations) of atomic orbitals from a single atom hybrid orbitals remain on central atom -molecular orbitals are combinations of atomic orbitals from 2 or more atoms. associated with entire molecule, not a single atom
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How many electrons can be placed into each MO of a molecule?
each MO, like each AO or hybrid, can hold a maximum of 2 electrons
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Can antibonding molecular orbitals have electrons in them?