Ortho-Dichlorobenzene, C₆H₄Cl₂, is obtained when two of the adjacent hydrogen atoms in benzene are replaced with Cl atoms. A skeleton of the molecule is shown here. (b) Are there any resonance structures for the molecule? If so, sketch them.

Consider the hypothetical molecule B-A=B. Are the following statements true or false? (a) This molecule cannot exist. (b) If resonance was important, the molecule would have identical A–B bond lengths.

An important reaction for the conversion of natural gas to other useful hydrocarbons is the conversion of methane to ethane. 2 CH₄(g) → C₂H₆(g) + H₂(g) In practice, this reaction is carried out in the presence of oxygen, which converts the hydrogen produced into water. 2 CH₄(g) + 12 O₂(g) → C₂H₆(g) + H₂O(g) Use Table 8.3 to estimate H for these two reactions. Why is the conversion of methane to ethane more favorable when oxygen is used? Why is the conversion of methane to ethane more favorable when oxygen is used?

Two compounds are isomers if they have the same chemical formula but different arrangements of atoms. Use Table 8.3 to estimate H for each of the following gas-phase isomerization reactions and indicate which isomer has the lower enthalpy. (d) Methyl isocyanide → Acetonitrile

The Ti2 + ion is isoelectronic with the Ca atom. (b) Calculate the number of unpaired electrons for Ca and for Ti²⁺.

The Ti²⁺ ion is isoelectronic with the Ca atom. (c) What charge would Ti have to be isoelectronic with Ca²⁺ ?

Consider the molecule C₄H₅N, which has the connectivity shown below. (a) After the Lewis structure for the molecule is completed, how many s and how many p bonds are there in this molecule?

(c) Hydrogen peroxide is sold commercially as an aqueous solution in brown bottles to protect it from light. Calculate the longest wavelength of light that has sufficient energy to break the weakest bond in hydrogen peroxide.

One scale for electronegativity is based on the concept that the electronegativity of any atom is proportional to the ionization energy of the atom minus its electron affinity: electronegativity = k1I - EA2, where k is a proportionality constant. (b) Why are both ionization energy and electron affinity relevant to the notion of electronegativity?

Acetylene (C₂H₂) and nitrogen (N₂) both contain a triple bond, but they differ greatly in their chemical properties. (b) By referring to Appendix C, look up the enthalpies of formation of acetylene and nitrogen. Which compound is more stable?

Acetylene (C₂H₂) and nitrogen (N₂) both contain a triple bond, but they differ greatly in their chemical properties. (c) Write balanced chemical equations for the complete oxidation of N₂ to form N₂O₅(g) and of acetylene to form CO₂(g) and H₂O(g). Write a balanced chemical equation for the complete oxidation of acetylene to form CO₂(g) and H₂O(g).

Acetylene (C₂H₂) and nitrogen (N₂) both contain a triple bond, but they differ greatly in their chemical properties. (e) Both N₂ and C₂H₂ possess triple bonds with quite high bond enthalpies (Table 8.3). Calculate the enthalpy of hydrogenation per mole for both compounds: acetylene plus H₂ to make methane, CH₄; nitrogen plus H₂ to make ammonia, NH₃.

A common form of elemental phosphorus is the tetrahedral P₄ molecule, where all four phosphorus atoms are equivalent: 

(b) How many P-P bonds are there in the molecule?

A common form of elemental phosphorus is the tetrahedral P₄ molecule, where all four phosphorus atoms are equivalent: 

Draw a Lewis structure for a linear P₄ molecule that satisfies the octet rule. Does this molecule have resonance structures?

Trifluoroacetic acid has the chemical formula CF₃CO₂H. It is a colorless liquid that has a density of 1.489 g/mL (a) Trifluoroacetic acid contains one CF₃ unit and is connected to the other C atom which bonds with both O’s. Draw the Lewis structure for trifluoroacetic acid.

Trifluoroacetic acid has the chemical formula CF₃CO₂H. It is a colorless liquid that has a density of 1.489 g/mL. (b) Trifluoroacetic acid can react with NaOH in aqueous solution to produce the trifluoroacetate ion, CF₃COO₂. Write the balanced chemical equation for this reaction.

Trifluoroacetic acid has the chemical formula CF₃CO₂H. It is a colorless liquid that has a density of 1.489 g/mL. (d) How many milliliters of a 0.500 M solution of NaOH would it take to neutralize 10.5 mL of trifluoroacetic acid?

Ammonium chloride, NH4Cl, is a very soluble salt in water. (c) If you dissolve 14 g of ammonium chloride in 500.0 mL of water, what is the molar concentration of the solution?