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.

Bond C C C H H H N N O O
Energy (kJ/mol) 602 411 432 942 494

Which of these is the strongest bond?

  • A C H
  • B C C
  • C N N
  • D O O
  • E H H

Q2:

Hydrogen molecules (H)2 have a single HH bond. This bond has an energy of 432 kJ/mol. What does this mean?

  • A432 kJ of energy is required to break one mole of HH bonds.
  • B432 kJ of energy is required to break each HH bond.
  • C432 kJ of energy is released when one mole of HH bonds is broken.
  • D432 kJ of energy is released when one HH bond is broken.
  • E432 kJ of energy is required to form one mole of HH bonds.

Q3:

The change in energy during a chemical reaction may be explained in terms of electrostatic interactions between subatomic particles. Which of the following best describes the change in energy when a covalent bond is formed?

  • ABond formation absorbs energy due to increased electrostatic attraction between protons and electrons.
  • BBond formation releases energy due to increased electrostatic attraction between protons.
  • CBond formation releases energy due to increased electrostatic attraction between protons and electrons.
  • DBond formation releases energy due to increased electrostatic repulsion between protons.
  • EBond formation absorbs energy due to increased electrostatic repulsion between protons and electrons.

Q4:

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.

4 S S S S S S S S S S

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

Q5:

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.

3 2 O O + O O O

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

Q6:

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.

3 C C H C H H H C H C H H C H H H H H C H C H H H

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.

Q7:

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

N N .

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

Q8:

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.

n n C C H H H H C C H H H H

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.

Q9:

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.

Element Energy Needed to Remove a Valence Electron (kJ/mol) Number of Protons in the Nucleus Number of Valence Electrons in the Atom Distance between Nuclei of Bonded Atoms (pm) Bond Energy of Diatomic (kJ/mol)
N 1,402 7 5 110 942
O 1,313 8 6 121 494
F 1,681 9 7 142 155

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.

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