(b) Why is it necessary a boiling point? What type of intermolecular forces must be overcome in converting each of the following from a liquid to a gas? (a) \( \mathrm{CO}_{2} \); (b) \( \mathrm{NH}_{3} \); (c) \( \mathrm{CHCl}_{3} \); (d) \( \mathrm{CCl}_{4} \).

### (b) Why is a Boiling Point Necessary? The **boiling point** of a substance is the temperature at which its vapor pressure equals the external (usually atmospheric) pressure, allowing the liquid to transition into a gas phase. Understanding the boiling point is essential for several reasons: 1. **Phase Transition Indicator:** It signifies the temperature at which a liquid changes to a gas, which is crucial in processes like distillation, evaporation, and various industrial applications. 2. **Intermolecular Forces Insight:** The boiling point provides information about the strength of intermolecular forces within a substance. A higher boiling point indicates stronger intermolecular attractions that require more energy to overcome. 3. **Purity Assessment:** Boiling points can help assess the purity of a substance. Pure compounds have characteristic boiling points, while impurities often cause deviations. 4. **Practical Applications:** Knowledge of boiling points is vital in everyday activities, such as cooking, refrigeration, and the formulation of products like paints and solvents. ### Intermolecular Forces to Overcome During Phase Transition When converting substances from a **liquid to a gas**, the molecules must overcome the **intermolecular forces (IMFs)** that hold them together in the liquid phase. Here's a breakdown for each specified compound: #### (a) **\( \mathrm{CO}_{2} \) (Carbon Dioxide)** - **Type of Intermolecular Forces:** **London Dispersion Forces (LDF)** - **Explanation:** Carbon dioxide is a linear, nonpolar molecule. It lacks permanent dipoles, so the primary intermolecular forces are temporary induced dipoles known as London dispersion forces. These are the weakest type of IMFs but are significant in gases like CO₂. #### (b) **\( \mathrm{NH}_{3} \) (Ammonia)** - **Type of Intermolecular Forces:** **Hydrogen Bonds and Dipole-Dipole Interactions** - **Explanation:** Ammonia is a polar molecule with a significant dipole moment. Additionally, the presence of hydrogen atoms bonded to a highly electronegative nitrogen atom allows for **hydrogen bonding**, a particularly strong type of dipole-dipole interaction. These forces must be overcome for ammonia to vaporize. #### (c) **\( \mathrm{CHCl}_{3} \) (Chloroform)** - **Type of Intermolecular Forces:** **Dipole-Dipole Interactions and London Dispersion Forces** - **Explanation:** Chloroform is a polar molecule due to the electronegative chlorine atoms, resulting in a permanent dipole moment. Therefore, it experiences dipole-dipole attractions. Additionally, being a relatively large molecule, it also has London dispersion forces. Both types of IMFs need to be overcome during vaporization. #### (d) **\( \mathrm{CCl}_{4} \) (Carbon Tetrachloride)** - **Type of Intermolecular Forces:** **London Dispersion Forces (LDF)** - **Explanation:** Carbon tetrachloride is a nonpolar molecule despite having polar C–Cl bonds because of its tetrahedral symmetry, which cancels out dipole moments. Consequently, the predominant intermolecular forces are London dispersion forces. ### Summary of Intermolecular Forces | **Compound** | **Types of Intermolecular Forces** | |--------------|-----------------------------------------------| | \( \mathrm{CO}_{2} \) | London Dispersion Forces | | \( \mathrm{NH}_{3} \) | Hydrogen Bonds, Dipole-Dipole Interactions | | \( \mathrm{CHCl}_{3} \) | Dipole-Dipole Interactions, London Dispersion Forces | | \( \mathrm{CCl}_{4} \) | London Dispersion Forces | Understanding these intermolecular forces helps in predicting and explaining the boiling points and other physical properties of these substances.