Bond Energy Practice Problems | Channels for Pearson+ (2024)

35 problems

1PRACTICE PROBLEMIn bonds formed, the lone pairs of electrons on one atom repel the lone pair of electrons on the other atom in the bond. Consider the following diatomic species: F2 (155 kJ/mol), Cl2 (242 kJ/mol), Br2 (193 kJ/mol), and I2 (151 kJ/mol). Why is the bond energy of F2 smaller than expected?
2PRACTICE PROBLEMThe bond dissociation energy decreases for the following bonds: H–F (570 kJ/mol), H–Cl (432 kJ/mol), H–Br (366 kJ/mol), and H–I (298 kJ/mol). Which of the statements below best explains why?
3PRACTICE PROBLEMConsider the following reaction P4(g) → 2 P2(g) with a ΔH° value of +229.1 kJ. If the P–P bond has an average bond dissociation energy of 197 kJ/mol, estimate the value of the P≡P triple bond energy in P2(g).
4PRACTICE PROBLEMEstimate the ΔH°rxn in kilojoules for the formation of methanethiol (CH3SH) from methanol (CH3OH):CH3OH(g) + H2S(g) → CH3SH(g) + H2O(g)
5PRACTICE PROBLEMEstimate the heat of combustion (in kJ) for propane, C3H8, using the following bond dissociation energies:
6PRACTICE PROBLEMFormaldehyde, CH2O is a pungent, colorless gas famous for its use to preserve tissues or cells. Using the bond dissociation energies and the ΔH°f = 716.7 kJ/mol for C(g), estimate the value of ΔH°f for CH2O at 25.0°C. Explain why the value obtained is only an estimate. The literature value of ΔH°f of CH2O is –108.6 kJ/mol.Average Bond Dissociation Energies: O=O: 498 kJ/mol, H–H: 436 kJ/mol, C–H: 410 kJ/mol, C=O: 732 kJ/mol
7PRACTICE PROBLEMThe relationship between the change in the potential energy and the separation between two atoms is illustrated in the figure below.Based on the figure, estimate the length of the bond formed between the two atoms.
8PRACTICE PROBLEMIn a Br2 molecule, the Br atoms are bonded by a double bond. Estimate the enthalpy of this bond using enthalpies of formation
9PRACTICE PROBLEMMethane burns according to this reaction:CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)Calculate the enthalpy of the reaction for this combustion reaction and for the combustion of ethane (C2H6). Identify which fuel produces more energy per mole upon combustion.
10PRACTICE PROBLEMAcetylene in nature is formed from the thermal decomposition of long-chain hydrocarbons at high temperatures (1700 K). Acetylene is a hydrocarbon composed of two carbon and two hydrogen atoms. The decomposition reaction for acetylene is:C2H2(g) → 2 C(s) + H2(g)Use bond energies to explain why this reaction is improbable. The bond energies are:H-H: 432 kJ/molC≡C: 839 kJ/molC-H: 413 kJ/mol
11PRACTICE PROBLEMConsider a photon with enough energy to break an N-N bond. Will the same photon be able to break an N-H bond based on average bond enthalpies?
12PRACTICE PROBLEMIdentify the bond that is most likely to be broken first when polyvinyl alcohol is subjected to extremely high temperature
13PRACTICE PROBLEMIdentify the bonds with the lowest bond enthalpy for polyvinyl alcohol.
14PRACTICE PROBLEMConsider the two reactions below:i) HBr(g) + H2O(g) ↔ Br-(g) + H3O+(g)ii) HI(g) + H2O(g) ↔ I-(g) + H3O+(g)Calculate the enthalpies of reaction using bond enthalpies and identify if both reactions are exothermic or not.
15PRACTICE PROBLEMConsider the two isomers of C6H14 below:Will there be a significant difference in the enthalpy of combustion of the two isomers?
16PRACTICE PROBLEMThe diagram shown below is a plot of potential energy as a function of the distance between the H and Br atoms. What would happen to the H—Br bond strength if the H—Br molecule is compressed at very high pressure?
17PRACTICE PROBLEMIs the following statement true of false?Shorter chemical bonds can store more energy than longer bonds.
18PRACTICE PROBLEMWhich two of the following nonmetallic elements would make the shortest single bond?B, H, S, and Br
19PRACTICE PROBLEMTwo compounds are said to be isomers of each other if they have the same molecular formula but different chemical structures. Calculate the reaction enthalpy for the gas-phase isomerization of methyl formate into acetic acid.Use the following bond enthalpies:C—C: 348 kJ/molC—H: 413 kJ/molC—O: 358 kJ/molO—H: 463 kJ/molC═O: 799 kJ/mol
20PRACTICE PROBLEMThe average C—C bond length in diamond is 154 pm while the average bond length in the H2 molecule is 74 pm. Using these bond lengths, predict the bond length for the C—H bond.
21PRACTICE PROBLEMThe average bond enthalpies for X and X bonds are:N—H: 391.0 kJ/molN—N: 163.0 kJ/molUsing these bond enthalpies, calculate the enthalpy of atomization for hydrazine (N2H4).
22PRACTICE PROBLEMThe average bond enthalpies for single, double, and triple hom*onuclear nitrogen bonds are given below:N—N: 163 kJ/molN═N: 418 kJ/molN≡N: 941 kJ/molCalculate the average contribution of a π-bond towards the bond enthalpy. What fraction of the N≡N bond enthalpy is represented by this contribution?
23PRACTICE PROBLEMPropane is a three-carbon alkane with the formula C3H8. Calculate the heat of combustion (ΔHrxn) for propane, first by using average bond energies and then by using its standard heat of formation. Calculate by what percent the two values differ and explain which value is expected to be more accurate.
24PRACTICE PROBLEMUnsaturated hydrocarbons react with chlorine to produce dichloro alkanes. Use a table of average bond energies to calculate the reaction enthalpy (ΔHrxn) for the following chlorination reaction:H3C—CH=CH2(g) + Cl2(g) → H3C—CH(Cl)—CH2—Cl(g)
25PRACTICE PROBLEMUse a table of average bond energies to calculate the heat of atomization for CCl2F2.
26PRACTICE PROBLEMThe heat of atomization is defined as the enthalpy change that accompanies the total breakdown of a molecule into its constituent atoms (gas phase). The heat of atomization of SiH4 is 1194 kJ/mol while it is 1351 kJ/mol for SiH3Cl. Using only this data, calculate the bond energy for the Si—Cl bond.
27PRACTICE PROBLEMWhich of the following set is arranged in order of INCREASING bond energy?
28PRACTICE PROBLEMRank the following bonds in order of increasingbond length.C–I C–O C–Br
29PRACTICE PROBLEMCalculate the ΔHrxn for the reaction between propanol and hydrogen bromide using bond energies.CH3CH2CH2OH(g) + HBr(g) → CH3CH2CH2Br(g) + H2O(g)
30PRACTICE PROBLEMEstimate the average molar bond enthalpy of the silicon-bromine bond in the SiBr4 molecule using the following values:ΔH Br(g) = 111.9 kJ/molΔH Si(g) = 450.0 kJ/molΔH SiBr4(g) = –415.5 kJ/mol
31PRACTICE PROBLEMPhosphoryl chloride (POCl3) can be formed from the reaction of phosphorus trichloride (PCl3) and oxygen gas (O2). The unbalanced reaction is shown below:PCl3(g) + O2(g) → POCl3(g)In POCl3, the O atom and the three Cl atoms are bonded to the central P atom. Referring to the given in the table below, calculate the approximate enthalpy of the reaction and determine whether the reaction is endothermic or exothermic.
32PRACTICE PROBLEMUsing bond enthalpies, calculate the ΔH for the given reaction below disregarding that ClF3 is a liquid.Cl2(g) + 3 F2(g) → 2 ClF3(l)
33PRACTICE PROBLEMIf methanol was used as a fuel, it would burn in the following manner: 2 CH3OH(l) + 3 O2(g) → 2 CO2(g) + 4 H2O(g).What is the ΔH°rxn using average bond energies?
34PRACTICE PROBLEMButan-1-ol is a possible fuel. Use average bond energies to calculate ΔHrxn for the combustion of butan-1-ol. C4H9OH(l) + 6 O2(g) → 4 CO2(g) + 5 H2O(g)
35PRACTICE PROBLEMHydrogenation reactions are used to add hydrogen across double bonds in hydrocarbons and other organic compounds. Use average bond energies to calculate ΔHrxn for the hydrogenation reaction.CH3–CH=CH2(g) + H2(g) → CH3–CH2–CH3(g)
Bond Energy Practice Problems | Channels for Pearson+ (2024)
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