Chem Exam 3

Calculate the approximate enthalpy change , ΔH∘, for the combustion of methane: CH4+2O2⇌2H2O+CO2 Use the values you calculated in Parts A to D, keeping in mind the stoichiometric coefficients.

-808 kJ

The formal charge on carbon in the molecule below is ________.

0

What is the value of the σ∗1s MO wave function at the nodal plane?

0

Due to the small and highly electronegative nature of fluorine, the oxyacids of this element are much less common and less stable than those of the other halogens. Bonding theory, however, does allow one to propose structures for these acids and use formal charges for the evaluation of these structures. For a molecule of fluorous acid, the atoms are arranged as HOFO. (Note: In this oxyacid, the placement of fluorine is an exception to the rule of putting the more electronegative atom in a terminal position.) What is the formal charge on each of the atoms? Enter the formal charges in the same order as the atoms are listed.

0,0,+1,-1

What is the total pressure (in atm) inside of a vessel containing N2 exerting a partial pressure of 0.256 atm, He exerting a partial pressure of 203 mmHg, and H2 exerting a partial pressure of 39.0 kPa?

0.908 atm

What is the density of methane, CH4, in a vessel where the pressure is 910 torr and the temperature is 255 K?

0.92 g/L

What is the maximum number of triple bonds that a carbon atom can form?

1

A helium balloon is filled to a volume of 5.60 L at 25∘C. What will the volume of the balloon become if it is put into liquid nitrogen to lower the temperature of the helium to 77 K?

1.4 L

An "empty" container is not really empty if it contains air. How may moles of oxygen are in an "empty" two-liter cola bottle at atmospheric pressure (101.325 kPa) and room temperature (25∘C)? Assume ideal behavior.

1.72 x 10-2 mol

What do you predict for the ideal values of the C−N−N and H−N−H angles, respectively?

109.5 and 109.5

The F-B-F bond angle in the BF3 molecule is _______

120

The angles between sp2 orbitals are ________.

120 degrees

PCl3Br2 is a nonpolar molecule. Based on this information, determine the Cl−P−Cl bond angle, the Br−P−Br bond angle, and the Cl−P−Br bond angle. Enter the number of degrees of the Cl−P−Cl, Br−P−Br, and Cl−P−Br bond angles, separated by commas (e.g., 30,45,90)

120, 180, 90 degrees

Calculate the bond dissociation energy needed to break all the bonds in a mole of carbon dioxide, CO2

1598 kJ/mol

Calculate the bond dissociation energy for the breaking of all the bonds in a mole of methane, CH4.

1652 kJ/mol

A double bond consists of ________ pairs of electrons shared between two atoms

2

What is the maximum number of double bonds that a carbon atom can form?

2

Calculate the volume the gas will occupy if the pressure is increased to 188 kPa while the temperature is held constant.

2.77 L

Part complete If 1.00 mol of argon is placed in a 0.500-L container at 30.0 ∘C, what is the difference between the ideal pressure (as predicted by the ideal gas law) and the real pressure (as predicted by the van der Waals equation)?

200 kPa

What is the partial pressure of oxygen in air at atmospheric pressure (101.325 kPa)? Assume ideal behavior.

21.28 kPa

What volume is occupied by one mole of gas at STP?

22.4 L

The molecular weight of a gas is ________ g/mol if 6.7 g of the gas occupies 6.3 L at STP.

24

If 50.75 g of a gas occupies 10.0 L at STP, 129.3 g of the gas will occupy ________ L at STP.

25.5

A triple bond consists of ________ pairs of electrons shared between two atoms.

3

There are ________ σ and ________ π bonds in the H - C≡C - H molecule.

3 and 2

The ion ICl4- has ________ valence electrons.

36

Part complete How many electrons are in the ππ system of the ozone molecule, O3?

4

What is the bond dissociation energy for breaking all the bonds in a mole of O2 molecules?

498 kJ/mol

PCl5 has ________ electron domains and a ________ molecular arrangement.

5, trigonal bipyramidal

How many nonbonding electron pairs are there in the Lewis structure of the peroxide ion, O22−?

6

An "empty" container is not really empty if it contains air. How may moles of nitrogen are in an "empty" two-liter cola bottle at atmospheric pressure (101.325 kPa) and room temperature (25∘C)? Assume ideal behavior.

6.38 x 10-2 mol

Calculate the volume the gas will occupy if the temperature is increased to 160 ∘C∘C while the pressure is held constant.

7.66 L

What is the partial pressure of nitrogen in air at atmospheric pressure (101.325 kPa)? Assume ideal behavior.

79.0 kPa

How many air molecules are in a 10.5×12.0×10.0 ft room (28.2 L=1 ft3)? Assume atmospheric pressure of 1.00 atm, a room temperature of 20.0 ∘C, and ideal behavior.

8.89 x 10 26 molecules

Calculate the bond dissociation energy required for breaking all the bonds in a mole of water molecules, H2O.

920 kJ/mol

By referring only to the periodic table, select the least electronegative element from among the following. Al, Si,P

Al

Based on the octet rule, aluminum most likely forms an ________ ion.

Al3+

Which of the following best describes what took place before the step pictured in the diagram?

An electron was promoted from the 3s orbital to the 3p orbital.

Of the following species, ________ will have bond angles of 120°.

BCl3

The boiling point of another member of this homologous series was found to be 309 K. What is the likely molecular formula for this compound?

C5H12

CHCl3 (61 ∘C) and CHBr3 (150 ∘C),

CHBr3 has the higher boiling point because it has the higher molar mass, which leads to greater polarizability and stronger dispersion forces

Which of these molecules has a Lewis structure with a central atom having no nonbonding electron pairs?

CO2, SiF4

Which of these elements is most likely to form ions with a 2+ charge?

Ca

Arrange the following elements in order of decreasing electronegativity. Chlorine, Selenium, Manganese, Cesium

Chlorine, Selenium, Manganese, Cesium

The element that would be expected to be the best insulator is

Cl

The element that would be the most effective at accepting electrons from another reagent is

Cl

Which statement best describes the polarity of SCl4F2?

Depending on the arrangement of outer atoms, this molecule could be polar or nonpolar.

By referring only to the periodic table, select the element that is most likely to form an ionic compound with Ba.

F

In the molecule below, which atom has the largest partial negative charge? Cl F. C Br I

F

The ________ ion has a noble gas electron configuration.

F-

By referring only to the periodic table, select the most electronegative element among the following.

Ga, P, Cl, Na

Which of the following bonds is the most polar?

H-F

Which of these molecules has the same number of shared and unshared electron pairs?

H2S

HF (20 ∘C) and HCl (-85 ∘C),

HF has the higher boiling point because hydrogen bonding is stronger than dipole-dipole forces.

The only noble gas without eight valence electrons is ________.

He

Br2 (59 ∘C) and ICl (97 ∘C).

ICl has the higher boiling point because it is a polar molecule.

If the pressure of the gas is doubled while the volume is held constant, what happens to its temperature?

If P is doubled, T increases by a factor of 2

Which of these kinds of interactions are broken when a liquid is converted to a gas?

Intermolecular interactions are broken when a liquid is converted to a gas

Which is generally stronger, intermolecular interactions or intramolecular interactions?

Intramolecular interactions are generally stronger.

Consider the following element combinations. Classify the bonds formed between each pair as ionic, polar covalent, or nonpolar covalent qualitatively based solely on each element's position on the periodic table. Do not conduct calculations.

Ionic- Ba and O, Al and N, Mn and Cl Polar Covalent- O and F, S and I, P and Cl Nonpolar Covalent- P and P, Cl and Cl

Based on the bond angles in CH4, NH3, and H2O, rank the magnitude of these repulsions. Rank from strongest to weakest repulsion. To rank items as equivalent, overlap them.

LP-LP, BP-LP, BP-BP

SO2

London dispersion forces, dipole-dipole bonding

Which ionic bond is predicted to be stronger?

Mg-Se

The Lewis structure of HCN (H bonded to C) shows that ________ has ________ nonbonding electron pair(s).

N,1

Which ABn molecule is trigonal pyramidal?

NH3

Ionic compounds are formed from ionic bonds, whereby an electron is transferred from the metal cation to the nonmetal anion. Ions form solid lattices of ions. Covalent compounds form solids through the attraction of two covalent molecules. Since the attraction between two covalent molecules is weak compared to the ionic bonds holding an ionic compound together, ionic compounds tend to have higher melting points. Which of the following compounds has the highest boiling point?

NaI

A Venus probe detects an element with a first ionization energy of 2088 kJ/mol. Given the table of known ionization energies provided in the introduction, what is the most likely identity of this element?

Ne

Which one of the following gases would deviate the least from ideal gas behavior?

Ne

By referring only to the periodic table, specify the most electronegative element in group 6A.

O

Which element has the highest (most negative) electron affinity?

O

For which of the following molecules or ions does the following description apply? "The bonding can be explained using a set of sp 2 hybrid orbitals, with one of the hybrid orbitals holding a nonbonding pair of electrons."

O3

Place the following elements in order of decreasing atomic radius: chlorine (Cl), lead (Pb), aluminum (Al), and fluorine (F)

Pb, Al, Cl, F

Which of the following actions would double the gas pressure?

Pushing down on the piston to halve the volume while keeping the temperature constant.

The element that is best able to form an ionic compound with sulfur is

Rb

Which of the following would have to lose two electrons in order to achieve a noble gas electron configuration?O Sr Na Se Br

Sr

What is the molecular geometry of a molecule with 3 outer atoms and 2 lone pairs on the central atom?

T-Shaped

Sometimes when we heat food in the microwave, the lid of the container pops off. Why does this occur?

The air and water vapor inside the container are expanding.

As a liquid metal such as mercury is cooled below its freezing point, what happens to the average distance between the atoms?

The average distance between the atoms decreases.

As a liquid metal such as mercury is cooled below its freezing point, what happens to the average kinetic energy of the atoms?

The average kinetic energy decreases.

Which statement best describes the polarity of CF2I2?

The molecule is always polar.

A certain AB4 molecule has a "seesaw" shape:(Figure 1). From which of the fundamental geometries shown in Figure 9.3 in the textbook (available from the eText link) could you remove one or more atoms to create a molecule having this seesaw shape?

Trigonal bipyramidal

What is the expected geometric shape of the following ABn molecule?

Trigonal pyramidal

The ________ ion is represented by the electron configuration [Ar]3d2.

V3+

What species has the electron configuration [Ar]3d2?

V3+

What is the electron configuration for the Co2+ ion?

[Ar]3d7

What is the electron configuration for the Fe3+ ion?

[Ar]4s03d5

The electron configuration of the phosphide ion (P3-) is ________.

[Ne]3s23p6

The electron configuration of the sulfide ion (S2-) is ________.

[Ne]3s23p6

To form a hydrogen bond, what must the non-hydrogen atom (N, O, or F) involved in the bond possess?

a nonbonding electron pair

Molecular Orbital theory correctly predicts diamagnetism of fluorine gas, F2. This is because ________.

all electrons in the MO electron configuration of F2 are paired.

Which of the following has eight valence electrons? Ti4+, Kr, Na+, Cl-

all of the above

What is the molecular geometry of a molecule with 2 outer atoms and 1 lone pair on the central atom?

bent

A typical triple bond ________.

consists of one σ bond and two π bonds

H2Se

dipole-dipole bonding, London dispersion forces

Atoms surrounded by eight valence electrons tend to lose electrons.

false

Electrons in core orbitals contribute to atom bonding.

false

Kinetic-molecular theory assumes that attractive and repulsive forces between gas particles are stronger than those between gas particles and container walls.

false

An ideal gas differs from a real gas in that the molecules of an ideal gas ________.

have no attraction for one another

A real gas will behave most like an ideal gas under conditions of ________.

high temperature and low pressure

CH3CH2OH

hydrogen-bonding, dipole-dipole bonding, London dispersion forces

A typical double bond ________.

imparts rigidity to a molecule is stronger and shorter than a single bond consists of two shared electron pairs consists of one σ bond and one π bond (all of the above)

How would you expect the pressure of a gas to change if suddenly the intermolecular forces were repulsive rather than attractive?

increase

Electronegativity ________ from left to right within a period and ________ from top to bottom within a group.

increases, decreases

In the mountains, water in an open container will boil when

its vapor pressure equals atmospheric pressure

The molecular geometry of the CS2 molecule is ________.

linear

A 3.00-L flask is filled with gaseous ammonia, NH3NH3. The gas pressure measured at 18.0 ∘C is 231 kPa . Assuming ideal gas behavior, how many grams of ammonia are in the flask?

mass of NH3= 4.87g

Classify each element as a metal, nonmetal, or semimetal. Cr, Sn, In, He, Cl, As

metal- Cr,Sn,In nonmetal- He, Cl semimetal- As

You would expect the velocity of ______________ to be larger mainly because _______________________________________________ when compared to the other hydrocarbon.

n-pentane, "the long, cylindrical shape results in stronger dispersion forces

You would expect the velocity of __________ to be larger mainly due to ___________________________________.

n-pentane, one more carbon atom in the chain

An AB4 molecule has two lone pairs of electrons on the A atom (in addition to the four B atoms). What is the electron-domain geometry around the A atom?

octahedral

An AB6 molecule has no lone pairs of electrons on the A atom. What is its molecular geometry?

octahedral

In addition to tetrahedral, another common shape for AB4 molecules is square planar. All five atoms lie in the same plane, with the B atoms at the corners of a square and the A atom at the center of the square. Which shape in the figure below could lead to a square-planar shape upon removal of one or more atoms?

octahedral

Based on the octet rule, phosphorus most likely forms a ________ ion.

p3-

Predict whether each of the following molecules is polar or nonpolar.

polar- CH3Br, NH3, SF3 nonpolar- XeF4, CCl4, GaH3

heat energy equation

q=mCpΔT, where q is the heat variable, m is the mass of the object, Cp is the specific heat constant and ΔT is the temperature change.

The hybridization of the carbon atom in carbon dioxide is ________.

sp

What type of hybrid orbital is produced in this hybridization?

sp3

For the AB4 molecule in Part B, predict the molecular geometry.

square planar

What is the molecular geometry of a molecule with 4 outer atoms and 2 lone pairs on the central atom?

square planar

The molecular geometry of the CHCl3 molecule is ________.

tetrahedral

In the space-filling model, what determines the relative sizes of the spheres?

the atomic radii

Molecular Orbital theory correctly predicts paramagnetism of oxygen gas, O2. This is because ________.

there are two unpaired electrons in the MO electron configuration of O2

Using the VSEPR model, the electron-domain geometry of the central atom in SO3 is ________.

trigonal planar

The molecular geometry of the H3O+ ion is ________.

trigonal pyramidal