The average bond enthalpies of the \(\mathrm{C}-\mathrm{Cl}\) and \(\mathrm{C}-\mathrm{F}\) bonds are \(340 \mathrm{~kJ} / \mathrm{mol}\) and \(485 \mathrm{~kJ} / \mathrm{mol}\), respectively. Based on this information, explain why the \(\mathrm{C}-\mathrm{Cl}\) bond in a CFC molecule is preferentially broken by solar radiation at \(250 \mathrm{nm}\).

Chemical bonds are the connections between atoms that enable the formation of chemical compounds. These bonds arise from the sharing or exchange of electrons among atoms and are categorized primarily into three types: ionic, covalent, and metallic bonds.

The strength of a bond is assessed by its bond enthalpy or bond dissociation energy, which is the energy required to break the bond between two atoms. In simple terms, bond enthalpy is a measure of the bond's strength. For example, in the exercise, the bond enthalpies for the C-Cl and C-F bonds are given as 340 kJ/mol and 485 kJ/mol respectively. This indicates that the C-F bond is stronger and thus requires more energy to break compared to the C-Cl bond.

Energy and Stability

Bonds with high bond enthalpy are more stable and tend to be less reactive. This is because the high energy required to break the bond often is not available in standard conditions, making these bonds less likely to break spontaneously. On the other hand, bonds with lower bond enthalpies are less stable and can be broken with relatively less energy input.

Solar radiation is the emission of energy from the sun that travels through space until it reaches the Earth. This radiation encompasses a range of wavelengths, including visible light, infrared light, and ultraviolet (UV) light. Notably, solar radiation is the primary source of natural light and heat for our planet.

Different wavelengths of solar radiation have varying amounts of energy. The energy of the radiation is inversely proportional to its wavelength—shorter wavelengths have higher energy and longer wavelengths have lower energy. For instance, UV light has a shorter wavelength and, therefore, higher energy compared to visible light.

Interactions with Chemical Bonds

When solar radiation encounters chemicals, it can cause reactions by breaking chemical bonds, particularly in susceptible molecules. Higher-energy radiation, like UV light, can break chemical bonds such as the ones found in certain atmospheric compounds or biological molecules, leading to profound effects like ozone layer depletion or skin damage.

Ultraviolet (UV) light is a type of electromagnetic radiation with a wavelength shorter than that of visible light but longer than X-rays. UV light typically ranges from 10 nm to 400 nm and is categorized into three types: UVA, UVB, and UVC, based on its wavelength. Among these, UVC has the shortest wavelength and, consequently, the highest energy.

The 250 nm wavelength mentioned in the exercise falls within the UVC range. The shorter the wavelength of UV light, the more energy it possesses, thus it has a greater capacity to initiate chemical reactions by breaking chemical bonds.

UV Light and Bond Breaking

The ability of UV light to break chemical bonds depends on the energy of the light and the bond enthalpy of the bond in question. At a wavelength of 250 nm, the UV light has sufficient energy to break the C-Cl bond with a bond enthalpy of 340 kJ/mol but is less likely to break the stronger C-F bond with a bond enthalpy of 485 kJ/mol, demonstrating that bond enthalpy is a crucial factor in determining how chemical bonds interact with UV radiation.