Explain the following on the basis of the behavior of atoms and/or ions. a. Cooking with water is faster in a pressure cooker than in an open pan. b. Melted sea ice from the Arctic Ocean produces fresh water. c. $\mathrm{CO}_{2}(s)(\text { dry ice ) does not have a normal boiling point }\( under normal atmospheric conditions, even though \)\mathrm{CO}_{2}$ is a liquid in fire extinguishers.

To understand the difference between cooking with a pressure cooker and an open pan, we need to understand the boiling point of water and the role pressure plays in this process. When heat is applied to water, the molecules gain energy and start moving faster, eventually breaking the bonds between them and transitioning from a liquid to a gas phase. In an open pan, as the water starts boiling at 100°C (212°F) under normal atmospheric pressure, the heat energy is mainly used for converting water into steam, rather than increasing the temperature further. The temperature remains constant at the boiling point during this phase change. In a pressure cooker, the situation is different. The container is sealed, which does not allow the steam to escape. This, in turn, increases the pressure inside the cooker. Since the boiling point of water increases as pressure increases, the water inside the pressure cooker can reach a higher temperature before turning into steam (about 120°C or 248°F at 15 psi above atmospheric pressure). A higher temperature means faster cooking.

The reason behind melted sea ice producing fresh water lies in the structure of ice crystals and the properties of salt ions in seawater. When seawater freezes into ice, water molecules form a crystal lattice structure, which has a specific arrangement with hydrogen bonds. The sodium (Na+) and chloride (Cl-) ions present in seawater do not fit into the lattice structure of ice. As a consequence, the majority of the salt ions are expelled during the freezing process and remain in the surrounding water, causing the ice to have a lower salt concentration. When the ice melts, the water molecules break the lattice arrangement, and the water formed from melted ice has a lower salt concentration than the original seawater. This results in fresh water.

Dry ice is the solid form of carbon dioxide (CO2). Unlike most substances, it does not have a normal boiling point under normal atmospheric conditions. The reason behind this is the process called sublimation. In the case of CO2, under normal atmospheric pressure, its solid form directly transitions into the gaseous state without passing through the liquid phase. This process is called sublimation. Thus, CO2 does not have a boiling point at normal atmospheric pressure, as boiling is the transition from the liquid to gas phase. However, under certain conditions of increased pressure, CO2 can indeed exist as a liquid. When CO2 is highly pressurized (above 5.1 atm), as in fire extinguishers, it is in its liquid state. When the pressure is released, CO2 rapidly expands and evaporates, turning into gas and effectively extinguishing fires.