Question

In which of the following processes is it necessary to break covalent bonds as opposed to simply overcoming intermolecular forces? (a) melting mothballs made of naphthalene (b) dissolving HBr gas in water to form hydrobromic acid (c) vaporizing ethyl alcohol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (d) changing ozone, \(\mathrm{O}_{3}\), to oxygen gas, \(\mathrm{O}_{2}\)

Short answer

a) Melting mothballs made of naphthalene b) Dissolving HBr gas in water to form hydrobromic acid c) Vaporizing ethyl alcohol, \({C}_{2} {H}_{5} {OH}\) d) Changing ozone, \({O}_{3}\), to oxygen gas, \({O}_{2}\) Answer: d) Changing ozone, \({O}_{3}\), to oxygen gas, \({O}_{2}\)

Step-by-step solution

Analyze the first option

Melting mothballs made of naphthalene: When naphthalene mothballs melt, the solid becomes a liquid. This process involves overcoming intermolecular forces between naphthalene molecules, allowing them to move more freely. However, the covalent bonds within each naphthalene molecule remain intact. Therefore, covalent bonds do not need to be broken for this process.

Analyze the second option

Dissolving HBr gas in water to form hydrobromic acid: When hydrogen bromide (HBr) gas dissolves in water, it forms hydrobromic acid. In this process, the HBr molecule does not break its covalent bond between the hydrogen and bromine atoms. Instead, it forms hydrogen bonds with water molecules, which is an intermolecular force. Therefore, covalent bonds do not need to be broken for this process.

Analyze the third option

Vaporizing ethyl alcohol, \({C}_{2} {H}_{5} {OH}\): Vaporizing ethyl alcohol requires overcoming intermolecular forces between the alcohol molecules, such as van der Waals forces, to change it from a liquid to a gas. The covalent bonds within each ethanol molecule remain intact during this process. Therefore, covalent bonds do not need to be broken for this process.

Analyze the fourth option

Changing ozone, \({O}_{3}\), to oxygen gas, \({O}_{2}\): When ozone changes to oxygen gas, the \({O}_{3}\) molecules break apart into \({O}_{2}\) molecules and individual oxygen atoms. This means the covalent bonds between the oxygen atoms in ozone must be broken and reformed as new covalent bonds between oxygen atoms in the \({O}_{2}\) molecules. Therefore, this process requires breaking covalent bonds.

Answer the question

Based on the analysis of each option, the process that requires breaking covalent bonds is (d) changing ozone, \({O}_{3}\), to oxygen gas, \({O}_{2}\). The other processes only require overcoming intermolecular forces.

Key concepts

Intermolecular Forces

Imagine molecules as friends holding hands. The strength of the forces between these friends dictates how closely they stick together. These interactions are what we call intermolecular forces. They are not as strong as the bonds that hold the atoms within a molecule together. However, they are crucial in determining the physical properties of substances like boiling and melting points.

There are several types of intermolecular forces, including:

• Van der Waals Forces: These are the weakest and occur between all molecules, whether polar or nonpolar.
• Dipole-Dipole Interactions: Occur only between polar molecules, and they are stronger than van der Waals forces.
• Hydrogen Bonds: This is a special dipole-dipole interaction that occurs when hydrogen is bound to a highly electronegative atom like oxygen, nitrogen, or fluorine.

When melting or boiling, a substance does not break covalent bonds. Instead, it overcomes these intermolecular forces, allowing the molecules to move more freely.

Chemical Reactions

Chemical reactions involve the breaking and forming of covalent bonds. This is fundamentally different from the physical processes like melting or dissolving, which typically involve overcoming intermolecular forces. In a chemical reaction, the structure of the molecules changes, and new substances are formed.

Take the conversion of ozone \(\mathrm{O}_{3}\) to oxygen gas \(\mathrm{O}_{2}\), for example. Initially, in ozone, the oxygen atoms are held together by covalent bonds. During this reaction, these bonds break, and new bonds form between the oxygen atoms, creating \(\mathrm{O}_{2}\). This process illustrates how chemical reactions require an actual reconfiguration of atoms, in contrast to merely altering how molecules arrange themselves.

States of Matter

The states of matter, namely solid, liquid, and gas, constitute the different phases that a substance can inhabit depending on temperature and pressure. These states are defined by the extent and types of intermolecular forces between molecules.

- **Solid:** Molecules are closely packed, and intermolecular forces are strong, giving solids a definite shape and volume. - **Liquid:** Molecules are less tightly packed compared to solids, allowing them to flow but still remaining relatively close due to moderate intermolecular forces. - **Gas:** Molecules have overcome intermolecular forces significantly, enabling them to move freely and fill the available volume.

Changes between these states, such as melting or boiling, involve changing the strength of intermolecular forces but do not break covalent bonds within the molecules themselves. These transitions are physical, meaning the chemical identity of the substance does not change.