Worksheet: Making and Breaking Chemical Bonds

In this worksheet, we will practice describing the making and breaking of chemical bonds and identifying the energy transfers involved.

Q1:

Listed in the table are the energies of selected chemical bonds.

BondCCCHHHNNOO
Energy (kJ/mol)602411432942494

Which of these is the strongest bond?

  • ACH
  • BCC
  • CNN
  • DOO
  • EHH

Q2:

The most stable form of elemental sulfur is the S8 molecule, a cyclic arrangement of single covalent bonds. Sulfur atoms can also form double covalent bonds, but the resulting S2 molecule is highly unstable and rapidly converts to S8. The equation for this reaction is given.

4SSSSSSSSSS

This reaction results in a large transfer of heat.

How many S2 double bonds are broken during the formation of one S8 molecule?

Why does the conversion of S2 to S8 result in a large transfer of heat?

  • AThe reaction releases energy because one sulfur-sulfur double bond is weaker than one single bond.
  • BThe reaction releases energy because one sulfur-sulfur double bond is stronger than one single bond.
  • CThe reaction absorbs energy because one sulfur-sulfur double bond is stronger than two single bonds.
  • DThe reaction absorbs energy because one sulfur-sulfur double bond is weaker than two single bonds.
  • EThe reaction releases energy because one sulfur-sulfur double bond is weaker than two single bonds.

Which bar chart illustrates the difference in bond energy between the single and double bonds of sulfur?

  • A
  • B
  • C
  • D
  • E

Q3:

The most stable form of elemental oxygen is the O2 molecule, which contains a double covalent bond. Molecules of O2 can react to form ozone, O3. The equation for this reaction is given.

32OO+OOO

This reaction results in a decrease in temperature.

How many OO double bonds are broken during the formation of one O3 molecule?

How many OO single bonds are created during the formation of one O3 molecule?

Why does the conversion of O2 to O3 result in a decrease in temperature?

  • AThe reaction is exothermic because one OO double bond is stronger than two single bonds.
  • BThe reaction is endothermic because one OO double bond is weaker than two single bonds.
  • CThe reaction is endothermic because one OO double bond is stronger than two single bonds.
  • DThe reaction is exothermic because one OO double bond is weaker than two single bonds.

Which bar chart illustrates the difference in bond energy between the single and double bonds of oxygen?

  • A
  • B
  • C
  • D
  • E

Q4:

The cyclic molecule cyclohexane can be formed from three molecules of ethene, as shown in the equation. Ethene contains a double bond between carbon atoms, while cyclohexane contains only single bonds.

3CCHCHHHCHCHHCHHHHHCHCHHH

The bond energies of single and double carbon-carbon bonds are shown in the bar chart.

Why is there a change in temperature during this chemical reaction?

  • AThere is an increase in temperature because one carbon-carbon double bond is stronger than two single bonds.
  • BThere is an increase in temperature because one carbon-carbon double bond is weaker than two single bonds.
  • CThere is a decrease in temperature because one carbon-carbon double bond is weaker than two single bonds.
  • DThere is a decrease in temperature because one carbon-carbon double bond is stronger than two single bonds.

Q5:

The most stable elemental form of nitrogen is the molecule N2, which contains a triple covalent bond, as shown:

NN.

Nitrogen atoms may also form single and double bonds with each other, but molecules containing these bonds are highly unstable. Which bar chart illustrates the difference in bond energy between the single, double, and triple bonds of nitrogen?

  • A
  • B
  • C
  • D
  • E

Q6:

Poly(ethene) contains a large number of carbon-carbon single bonds. The figure shows the production of the polymer from the alkene ethene, which contains only carbon-carbon double bonds. Conversion of ethene to poly(ethene) is highly exothermic.

nnCCHHHHCCHHHH

A poly(ethene) molecule with 𝑛 repeat units is formed from 𝑛 molecules of ethene. For each carbon-carbon double bond involved in this reaction, how many single bonds are present in the product?

Why is the conversion of ethene to poly(ethene) highly exothermic?

  • AA carbon-carbon double bond is weaker than two carbon-carbon single bonds.
  • BA carbon-carbon double bond is stronger than two carbon-carbon single bonds.
  • CThe product contains more bonding electrons than the reactant.
  • DThe reaction converts a gas to a solid.
  • EA carbon-carbon single bond is weaker than a CH bond.

Why does ethene remain unreacted at room temperature and pressure?

  • AThe activation energy is small.
  • BThe reaction is inhibited by air.
  • CThe activation energy is large.
  • DPolymer formation absorbs heat.
  • EPolymer formation releases heat.

Q7:

Several elements occur naturally as diatomic molecules. Listed in the table are several atomic properties of the elements N,O, and F, and the bond energies of their diatomic molecules.

ElementEnergy Needed to Remove a Valence Electron (kJ/mol)Number of Protons in the NucleusNumber of Valence Electrons in the AtomDistance between Nuclei of Bonded Atoms (pm)Bond Energy of Diatomic (kJ/mol)
N1,40275110942
O1,31386121494
F1,68197142155

Which of the following is the best explanation for the large change in bond energy between N2 and F2?

  • AThe distance between nuclei increases, resulting in more electrostatic repulsion between atoms.
  • BThe distance between nuclei and shared valence electrons increases, resulting in less electrostatic attraction between atoms.
  • CThe energy needed to remove a valence electron increases, resulting in less electrostatic attraction between atoms.
  • DThe number of shared valence electrons decreases, resulting in less electrostatic attraction between atoms.
  • EThe charges of the nuclei increase, resulting in more electrostatic repulsion between atoms.

Q8:

The substitution reaction between methane and fluorine gases is represented by the following equation. CH+FCHF+HF423 The bond enthalpies of the reactants and products are listed in the table.

BondCFCHFFHF
Bond Enthalpy (kJ/mol)485411155565

What is the enthalpy change for the substitution reaction?

Q9:

In the Andrussow oxidation, methane, ammonia, and oxygen react to produce hydrogen cyanide (HCN) and water. The energies of selected bonds are listed in the table.

BondCHNHOHOOOOCNCNCN
Bond Energy (kJ/mol)411386459142494305615887

Give a balanced chemical equation for this reaction.

  • A2CH+4NH+9O4HCN+18HO4322
  • B2CH+2NH+5O2HCN+10HO4322
  • CCH+NH+2OHCN+4HO4322
  • D4CH+2NH+7O2HCN+14HO4322
  • E2CH+2NH+3O2HCN+6HO4322

Calculate the total energy change for this reaction per mole of hydrogen cyanide produced.

Q10:

In the Haber process, nitrogen and hydrogen gases react reversibly to produce gaseous ammonia (NH)3. There are no other products. The energies of selected bonds are listed in the table.

BondNNNNNNHHNH
Bond Energy (kJ/mol)167418942432386

Give a balanced chemical equation for this reaction.

  • AN+6H4NH223
  • BN+6H2NH223
  • C2N+4H3NH223
  • D2N+3H4NH223
  • EN+3H2NH223

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

Q11:

Alkanes from the fractional distillation of crude oil can be converted to more reactive alkenes by catalytic cracking. In the cracking of pentane (CH)512, one alkene and one alkane are produced. The energies of selected bonds are listed in the table.

BondCHCCCCCC
Bond Energy (kJ/mol)411346602835

Calculate the total change in bond energy for this reaction per mole of pentane reacted.

Q12:

The complete combustion of methane produces water and carbon dioxide gases as the only products. Using the bond energies listed in the table, calculate the total change in bond energy for this reaction, per mole of methane combusted. Note that it may not be necessary to use all of the energy values shown.

BondCHCOCOCOOHOOOO
Bond Energy (kJ/mol)4113587991,072459142494

Q13:

The complete combustion of ethene (CH)24 produces water and carbon dioxide gases as the only products. Using the bond energies listed in the table, calculate the total change in bond energy for this reaction, per mole of ethene combusted.

BondCHCCCCCOCOCOOHOOOO
Bond Energy (kJ/mol)4113466023587991,072459142494

Q14:

The complete combustion of heptene (CH)714 produces water and carbon dioxide gases as the only products. Using the bond energies listed in the table, calculate the total change in bond energy for this reaction, per mole of heptene combusted.

BondCHCCCCCOCOCOOHOOOO
Bond Energy (kJ/mol)4113466023587991,072459142494

Q15:

Polytetrafluoroethylene (PTFE), a polymer widely used in lubricants and nonstick coatings, is produced from tetrafluoroethene:

CFFCFF

Tetrafluoroethene is synthesized via two reaction steps. In the first step, chloroform (CHCl)3 reacts with hydrogen fluoride gas to form chlorodifluoromethane (CHClF)2. In the second step, chlorodifluoromethane is converted to tetrafluoroethene. Both reactions generate hydrogen chloride gas as the only other product. The energies of selected bonds are shown in the table.

BondHFHClCHCFCClCCCCCH
Bond Energy (kJ/mol)565428411485327346602411

Calculate the total change in bond energy when one mole of chloroform is converted to chlorodifluoromethane.

Calculate the total change in bond energy when one mole of chloroform is converted to tetrafluoroethene.

Q16:

Acrylonitrile (CHN)33 is used in the production of synthetic rubbers and other polymeric materials. The main method for synthesizing acrylonitrile is to react propene gas (CH)36 with ammonia and oxygen at high temperature. The bonds in these molecules have different energies, as indicated in the diagram. All labeled bond energies are in units of kilojoules per mole.

+60241134664592+4943+38626024112887OHHCCCHHHHHHOOHNHHCCCHNHH

Calculate the total change in bond energy for this reaction per mole of acrylonitrile produced.

Q17:

Ozone is a pungent pale blue gas involved in many important reactions in the atmosphere. It is generated reversibly from oxygen gas and reacts with nitric oxide (NO) to produce nitrogen dioxide (NO)2 and nitrogen trioxide (NO)3. The bonds in these molecules have different energies, some of which are shown in the diagram. All bond energies are in units of kilojoules per mole.

379626466494NONOONOOOOO

For the reaction O+NONO+O322, the total change in bond energy per mole of ozone reacted is 202 kJ/mol.

Calculate the total change in bond energy when one mole of nitrogen trioxide is produced from ozone and nitrogen dioxide.

Calculate the total change in bond energy when one mole of ozone is produced from oxygen gas.

Q18:

Atmospheric nitrogen dioxide (NO)2 reacts with methanol (CHOH)3 generated from organic pollutants. This reaction produces nitric acid (HNO)3 and methyl nitrite, a highly oxidizing species. The bonds in these molecules have different energies, as illustrated in the diagram. All labeled bond energies are in units of kilojoules per mole.

205466423500377411437345398177607OHCHHHNOONOOOHOCNHHHO

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

Q19:

Acetylene (CH)24 can react with a wide variety of compounds to produce useful organic compounds containing carbon-carbon double bonds. The average energies of selected bonds are listed in the table.

BondHHHClHBrCCCCCCCClCBrCH
Bond Energy (kJ/mol)432428362346602835327285411

By calculating the total changes in bond energy per mole of acetylene reacted, place the following reactions in order from the most exothermic to the least.

+++2.1.3.CHCHCCHHClHHClCHCHCHHCHHHHCCHHCHCHHBrHBr
  • A2, 3, 1
  • B1, 3, 2
  • C1, 2, 3
  • D3, 2, 1
  • E2, 1, 3

Q20:

Nitric oxide (NO) is a colorless gas produced industrially by the reaction of ammonia (NH)3 with oxygen at high temperature. Reaction with further oxygen may generate nitrogen dioxide (NO)2, a toxic brown gas that is a strong contributor to air pollution. The bonds in these molecules have different energies, as indicated in the diagram. All labeled bond energies are in units of kilojoules per mole.

494459386626466NONOOOHHNHHHOO

Calculate the total change in bond energy when one mole of nitric oxide is produced from ammonia and oxygen.

Calculate the total change in bond energy when one mole of nitrogen dioxide is produced from ammonia and oxygen.

Q21:

Phosgene (COCl)2 is a highly toxic gas with the structure shown.

CClClO

The reaction of phosgene with water generates carbon dioxide and hydrochloric acid as the only products. Using the bond energies listed in the table, calculate the total change in bond energy for this reaction, per mole of phosgene reacted.

BondCHOHClHCOCOCOCCl
Bond Energy (kJ/mol)4114594283587991,072327

Q22:

Thionyl chloride (SOCl)2 is a reactive compound used in a number of important industrial processes. The compound can be produced from sulfur dioxide (SO)2, sulfur trioxide (SO)3, sulfur dichloride (SCl)2, and chlorine gases in a number of ways: Reaction1:SO+SClSOCl+SOReaction2:SO+2SCl+Cl3SOClReaction3:SO+SCl+Cl2SOCl322232222222,,. For each mole of sulfur trioxide reacted, the total change in bond energy for Reaction 3 is 89 kJ/mol. Calculate the total change in bond energy for Reaction 1, per mole of sulfur trioxide reacted, to the nearest kJ/mol.

456242435243240SOOOSClClSClClOClCl

Q23:

In which of these reaction profile diagrams is the energy required to break chemical bonds the greatest?

  • A(c)
  • B(a)
  • C(d)
  • D(b)

Q24:

The reaction profile diagram for an endothermic reaction is shown below.

Which arrow corresponds to the energy absorbed in order to break chemical bonds?

  • AC
  • BA
  • CB

Which arrow corresponds to the energy released through the making of chemical bonds?

  • AB
  • BA
  • CC

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