Worksheet: Bond Energy

In this worksheet, we will practice using net changes in bond energy during reactions to calculate the bond energies of reactants and products.

Q1:

To the nearest kJ/mol, what is the bond energy of HCl? H()+Cl()2HCl()kJmol22rgggΔ𝐻=βˆ’184.7/⦡

BondHHClCl
Bond Energy (kJ/mol)436243

Q2:

Ethene and iodine react to form 1,2-diiodoethane. The equation for this reaction is shown.

+CHCHHHIIHCHICHIH

The total energy change per mole of ethene reacted is βˆ’24 kJ/mol. The energies of selected bonds in the reactants and products are given in the table.

BondC–CCCC–HII
Energy (kJ/mol)346602411148

Calculate, to the nearest kilojoules per mole, the bond energy of the C–I bond.

Q3:

Which of the following hydrogen halides has the smallest bond enthalpy?

  • AHCl
  • BHBr
  • CHI
  • DHF

Q4:

Which of the following diatomic systems has the largest bond enthalpy?

  • ACO
  • BSnO
  • CGeO
  • DPbO
  • ESiO

Q5:

Ammonia (NH3) is a key starting material for the manufacture of fertilizers. The compound is produced by the reaction of nitrogen and hydrogen gases at high temperature and pressure. The energies of selected bonds are given in the table.

BondN–NNNNNH–H
Energy (kJ/mol)167418942432

The total energy change per mole of ammonia produced is βˆ’46 kJ/mol. Calculate, to the nearest kJ/mol, the energy of the N–H bond in NH3.

Q6:

Cracking of hexane produces a mixture of hydrocarbons. One possible cracking pathway is described by the following equation.

+CHHHCCHHHHCCHHCHHHHCHHCCHHHHHCHHCHHCHHHH

The total energy change per mole of hexane reacted is +90 kJ/mol.

How many C–C single bonds are lost for every C–C double bond formed?

Why is the total energy change for this reaction a positive number?

  • AOne C–C double bond has higher bond energy than one C–C single bond and one C–H bond.
  • BOne C–C double bond has higher bond energy than two C–C single bonds.
  • COne C–C double bond has lower bond energy than one C–C single bond.
  • DOne C–C double bond has lower bond energy than two C–C single bonds.
  • EOne C–C double bond has lower bond energy than one C–C single bond and one C–H bond.

The C–H bonds in hexane can be slightly strengthened by replacing the H atoms with atoms of deuterium, a heavy hydrogen isotope. How and why does this modification affect the total energy change for the cracking reaction?

  • AThe total energy change decreases because more energy is needed to break the C–H bonds.
  • BThe total energy change decreases because more energy is released when C–H bonds are formed.
  • CThe total energy change remains the same because the C–H bond energy is very small.
  • DThe total energy change increases because more energy is needed to break the C–H bonds.
  • EThe total energy change remains the same because no C–H bonds are broken or formed.

An alternative cracking reaction converts hexane to methane (CH4) and a second molecule. Which of the following best describes the total energy change for this cracking pathway?

  • AThe total energy change is greater than +90 kJ/mol because more bonds are broken and fewer are formed.
  • BThe total energy change is greater than +90 kJ/mol because the same number of bonds is broken and fewer are formed.
  • CThe total energy change is less than +90 kJ/mol because fewer bonds are broken and the same number is formed.
  • DThe total energy change is +90 kJ/mol because the same number of bonds is broken and formed.
  • EThe total energy change is less than +90 kJ/mol because fewer bonds are broken and more are formed.

Q7:

Chlorine gas reacts with hydrogen bromide to produce bromine and hydrogen chloride. The reaction of 1 mole of chlorine releases 82 kJ of energy. The energies of selected bonds in the reactants and products are given in the table.

Bond H–ClH–BrCl–Cl
Energy (kJ/mol) 428 362 240

Write a balanced chemical equation for this reaction.

  • ACl+2HBrBr+2HCl22
  • B2Cl+HBr2Br+HCl22
  • CBr+HClCl+HBr22
  • DBr+2HClCl+2HBr22
  • ECl+HBrBr+HCl22

Calculate, to the nearest kilojoule per mole (kJ/mol), the energy of the Br–Br bond.

Q8:

Nitric oxide (NO) is produced by the reaction of nitrogen and oxygen in the air during a lightning strike. The equation for this reaction is as shown. N+O2NO22

The total energy change for this reaction per mole of nitrogen reacted is +185 kJ/mol. The energies of selected bonds are given in the table.

BondN–NNNNNOO
Energy (kJ/mol)167418942494

Calculate, to the nearest kilojoule per mole (kJ/mol), the energy of the N–O bond.

Q9:

Chloromethane is produced by the reaction of methane (CH)4 with chlorine gas in the presence of UV light. The equation for this reaction is shown.

The reaction of 1.00 mol of methane releases 104 kJ of energy. The energies of selected bonds in the reactants and products are given in the table.

BondH–ClCl–ClC–H
Energy (kJ/mol)428240411

Calculate, to the nearest kilojoule per mole (kJ/mol), the energy of the C–Cl bond.

Q10:

Ethanethiol, a volatile liquid with a strong smell, is added to liquefied petroleum gas to aid the detection of gas leaks. The compound is produced by reacting ethene with hydrogen sulfide (HS2), according to the shown equation.

The total energy change for this reaction is βˆ’69 kJ/mol. The energies of selected bonds are given in the table.

BondC–CCCC–HC–S
Energy (kJ/mol)346602411272

Calculate, to the nearest kilojoule per mole (kJ/mol), the average energy of the S–H bonds in HS2 and ethanethiol.

Q11:

Nitrogen trifluoride reacts with hydrogen chloride to produce hydrogen fluoride, chlorine, and nitrogen. The equation for this reaction is shown.

+266+3+FNFFHClHFClClNN

The total energy change per mole of N2 produced is βˆ’834 kJ/mol. The energies of selected bonds are given in the table.

Bond H–ClH–FCl–ClF–FNNNN
Energy (kJ/mol) 428 565 240 155 418 942

Calculate, to the nearest kilojoule per mole, the bond energy of the N–F bond.

Q12:

The displayed formulas of ethane, ethene, and ethyne are shown.

The energies of the bonds in these molecules are given in the table.

Bond CHCCCCCC
Energy (kJ/mol) 411 346 602 835

What is the difference in total bond energy between ethane and ethene?

What is the difference in total bond energy between ethene and ethyne?

When one hydrogen molecule reacts with one molecule of ethene or ethyne, energy is released and a new hydrocarbon is produced. For which of the two hydrocarbons is the reaction most exothermic, and why?

  • AEthyne, because the energy of the CC bond is closer to the energy of two C–H bonds
  • BEthene, because this compound has smaller total bond energy
  • CEthene, because there is a greater energy difference between CC and CC than between CC and CC
  • DEthyne, because there is a greater energy difference between CC and CC than between CC and CC
  • EEthyne, because this compound has greater total bond energy

Q13:

Sulfur dichloride (SCl)2 decomposes reversibly to produce disulfur dichloride (SCl)22 and chlorine.

+2SClClClClSClSCl

The total energy change per mole of SCl22 produced is +44 kJ/mol. The energies of selected bonds are given in the table.

Bond SClClCl
Energy (kJ/mol) 255 240

Calculate the energy of the S–S bond in SCl22.

Q14:

White phosphorus (P)4 consists of highly reactive pyramid-shaped molecules with a PP bond energy of 201 kJ/mol. Oxygen (bond energy 494 kJ/mol) may react with white phosphorus to produce the cage-like molecule tetraphosphorus hexoxide (PO)46. The equation for this reaction is as follows.

+3OOPPPPPOOOPPPOOO

This reaction is highly exothermic, releasing 1,666 kJ of energy per mole of white phosphorus. Calculate, to the nearest kJ/mol, the energy of the PO bonds in tetraphosphorus hexoxide.

Q15:

Shown in the figure are two reactions involving sulfur dioxide (SO2) and sulfur trioxide (SO3). The total energy changes for the reactions, Δ𝐻, are given per mole of SO2 reacted.

The energies of selected bonds are given in the table.

Bond SO in SO2OOFF
Energy (kJ/mol) 533 494 155

Calculate, to the nearest kilojoule per mole, the energy of the SO bond in SO3.

Calculate, to the nearest kilojoule per mole, the energy of the OF bond in OF2.

Q16:

Chlorine dioxide (ClO)2 and dichlorine monoxide (ClO)2 are highly reactive compounds that can decompose into elemental chlorine (bond energy 240 kJ/mol) and oxygen (bond energy 494 kJ/mol). The structural formulas of the two molecules are shown in the figure.

ClOClOClO

The decomposition of 1 mole of ClO2 releases 104 kJ of energy, while the decomposition of 1 mole of ClO2 releases 87 kJ of energy. Calculate, to the nearest kilojoule per mole, the difference in bond energy between ClO2 and ClO2.

Q17:

Phosphorus trifluoride (PF3) reacts with fluorine to produce phosphorous pentafluoride (PF5). The equation for this reaction is as follows.

The energy of each PF bond in PF3 is 501 kJ/mol and the energy of the FF bond in fluorine is 155 kJ/mol. The total energy change for the reaction is βˆ’637 kJ/mol. Calculate, to the nearest kilojoule per mole, the average energy of a PF bond in PF5.

Q18:

Iodine monofluoride (IF) decomposes at 0∘C to produce iodine pentafluoride (IF5) and elemental iodine. The equation for this reaction is as follows.

The average energy of an IF bond in IF5 is 230 kJ/mol, and the energy of the II bond is 148 kJ/mol. The total energy change for the reaction, per mole of IF5 formed, is βˆ’51 kJ/mol.

What value of (a) results in a balanced chemical equation?

What value of (b) results in a balanced chemical equation?

To the nearest kilojoule per mole, what is the energy of the IF bond in IF?

Q19:

The water-gas shift reaction is a major source of hydrogen gas for industrial processes. In this reaction, carbon monoxide is reacted with steam to produce hydrogen and carbon dioxide: CO+HOCO+H222.

The energies of selected bonds are listed in the table. Calculate the total change in bond energy for this reaction, per mole of hydrogen gas produced.

BondHHCHOHCOCOCO
Bond Energy (kJ/mol)4324114593587991,072

Q20:

Under UV light, hydrogen and chlorine gases react reversibly to form hydrogen chloride: H+Cl2HCl22. Using the bond energies listed in the table, calculate the total change in bond energy for this reaction, per mole of hydrogen gas reacted.

BondHHHClClCl
Bond Energy (kJ/mol)432428240

Q21:

Acetic anhydride, an industrially useful reactive compound, can be synthesized in a number of steps from methyl acetate and carbon monoxide.

+CHHHCOOCCOHHHCHCHHOOCHHHCO

The reactions are performed in a solution containing catalytic salts. The average energies of selected bonds are listed in the table.

BondCHCCCCCCCOCOCO
Bond Energy (kJ/mol)4113466028353587991,072

Calculate the total change in bond energy for this process, per mole of acetic anhydride produced.

The calculated change in bond energy for this process is likely to differ from the measured enthalpy change. Which of the following factors does not contribute to this discrepancy?

  • ABond energies are affected by the other bonds in a molecule.
  • BThe enthalpy change is affected by the presence of a catalyst.
  • CBond energies vary with the reaction temperature.
  • DHeat losses cause the measured enthalpy change to be larger than the true value.
  • EThe enthalpy change is affected by interactions with the solvent.

Q22:

Dinitrogen tetroxide (NO)24 is a reactive molecule used in chemical synthesis and used as a rocket propellant. Each molecule of dinitrogen tetroxide is formed reversibly by the reaction of two molecules of nitrogen dioxide (NO)2. The bonds in these molecules have different energies, as indicated in the diagram. All labeled bond energies are in units of kilojoules per mole.

1674662438NONOOOONO

Calculate the total change in bond energy for this reaction, per mole of dinitrogen tetroxide produced.

Q23:

Hydrogen peroxide (HO)22 is a highly reactive material used as a bleaching agent and rocket fuel. The compound slowly decomposes in the presence of light to form water and oxygen. The equation for this reaction is shown.

+light22OHOHOOOHH

The total energy change per mole of oxygen formed is βˆ’210 kJ/mol. The energies of selected bonds in the reactants and products are given in the table.

Bond OOOH
Energy (kJ/mol) 494 473

Calculate, to the nearest kJ/mol, the energy of the O–O bond in HO22.

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