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Problem 105a
If hydrogen were used as a fuel, it could be burned according to this reaction: H2(g) + 1/2 O2(g) → H2O(g) Use average bond energies to calculate ΔHrxn for this reaction.
Problem 105b
If hydrogen were used as a fuel, it could be burned according to this reaction: H2(g) + 1/2 O2(g) → H2O(g) Use average bond energies to calculate ΔHrxn for the combustion of methane (CH4).
Problem 105c
If hydrogen were used as a fuel, it could be burned according to this reaction: H2(g) + 1/2 O2(g) → H2O(g) Which fuel yields more energy per mole?
Problem 105d
If hydrogen were used as a fuel, it could be burned according to this reaction: H2(g) + 1/2 O2(g) → H2O(g) Which fuel yields more energy per gram?
Problem 106
Calculate ΔHrxn for the combustion of octane (C8H18), a component of gasoline, by using average bond energies and then calculate it using enthalpies of formation from Appendix IIB. What is the percent difference between your results? Which result would you expect to be more accurate?
Problem 107a
Draw the Lewis structure for each compound. a. Cl2O7 (no Cl–Cl bond)
Problem 107b
Draw the Lewis structure for each compound. b. H3PO3 (two OH bonds)
Problem 107c
Draw the Lewis structure for each compound. c. H3AsO4
Problem 108
The azide ion, N3-, is a symmetrical ion, all of whose contributing resonance structures have formal charges. Draw three important contributing structures for this ion.
Problem 109
List the following gas-phase ion pairs in order of the quantity of energy released when they form from separated gas-phase ions. List the pair that releases the least energy first. Na+ F-, Mg2+F-, Na+O2-, Mg2+O2-, Al3+O2-.
Problem 111
The heat of atomization is the heat required to convert a molecule in the gas phase into its constituent atoms in the gas phase. The heat of atomization is used to calculate average bond energies. Without using any tabulated bond energies, calculate the average C–Cl bond energy from the following data: the heat of atomization of CH4 is 1660 kJ/mol, and the heat of atomization of CH2Cl2 is 1495 kJ/mol.
Problem 112
Calculate the heat of atomization (see previous problem) of C2H3Cl, using the average bond energies in Table 9.3.
Problem 113
A compound composed of only carbon and hydrogen is 7.743% hydrogen by mass. Propose a Lewis structure for the compound.
Problem 114
A compound composed of only carbon and chlorine is 85.5% chlorine by mass. Propose a Lewis structure for the compound.