In which of the following processes is it necessary to break covalent bonds as opposed to simply overcoming intermolecular forces? (a) subliming dry ice (b) vaporizing chloroform \(\left(\mathrm{CHCl}_{3}\right)\) (c) decomposing water into \(\mathrm{H}_{2}\) and \(\mathrm{O}_{2}\) (d) changing chlorine molecules into chlorine atoms

Let's analyze each process one by one. (a) Subliming dry ice: Dry ice is solid carbon dioxide (CO₂), and sublimation is the process of turning a solid directly into a gas. During this process, only the intermolecular forces holding the CO₂ molecules together in the solid state are broken, and the covalent bonds within each CO₂ molecule remain intact. (b) Vaporizing chloroform (CHCl₃): Chloroform is a chemical compound with the formula \(\mathrm{CHCl}_{3}\). Vaporizing chloroform involves turning a liquid into a gas. This process only requires breaking the intermolecular forces between the molecules, not the covalent bonds within the \(\mathrm{CHCl}_{3}\) molecules. (c) Decomposing water into H₂ and O₂: Water (H₂O) molecules are composed of hydrogen and oxygen atoms, held together by covalent bonds. To decompose water into hydrogen (H₂) and oxygen (O₂) gas molecules, we need to break the covalent bonds between the H and O atoms in the water molecules. (d) Changing chlorine molecules into chlorine atoms: Chlorine molecules consist of two chlorine atoms, which are held together by a covalent bond. To convert a chlorine molecule into separate chlorine atoms, we need to break the covalent bond between the atoms.

Based on our analysis, we can see that: - (a) and (b) only involve overcoming intermolecular forces, so they do not require breaking covalent bonds. - (c) and (d) involve breaking covalent bonds within the molecules or between atoms. Thus, the processes in which it is necessary to break covalent bonds are: (c) decomposing water into \(\mathrm{H}_{2}\) and \(\mathrm{O}_{2}\), and (d) changing chlorine molecules into chlorine atoms.