Final answer:
The maximum capacity by weight of a portable CO₂ extinguisher varies. Below the critical temperature of 31 °C, liquid CO₂ can exist inside. Above this temperature, it stays in a gaseous state regardless of pressure, explaining the lack of liquid sound on hot days.
Step-by-step explanation:
The maximum capacity, by weight, of a portable CO₂ extinguisher can vary. However, the question seems to be more focused on understanding the behavior of CO₂ under different temperatures. The critical temperature of carbon dioxide is 31 °C (304 K). Below this temperature, CO₂ can exist as a liquid within the fire extinguisher, which would explain why we can hear it sloshing around on a cool day at 18 °C. However, above 31 °C, CO₂ cannot be liquefied regardless of pressure, so on a hot day at 35 °C, the extinguisher will not have liquid CO₂ inside.
Looking at the provided exercise, when the CO₂ fire extinguisher's temperature rises above its critical temperature due to being left in a car on a hot day, the pressure inside will increase as the CO₂ cannot liquefy, potentially posing a safety hazard. This is why fire extinguishers come with warnings to store them below certain temperatures, typically 120 °F (48.8 °C). The exercises provided also illustrate examples of how pressure and volume of gases change with temperature, a concept described by the ideal gas law.