Final answer:
Solid carbon dioxide, or dry ice, sublimes directly to CO2 gas at 1 atm pressure, as liquid CO2 cannot exist under normal atmospheric conditions.
Step-by-step explanation:
The relationship between solid carbon dioxide and carbon dioxide gas after all of the solid has changed to gas is that the solid sublimes directly into the gas phase under normal atmospheric pressure (1 atm). This is explained by examining the phase diagram for carbon dioxide, which shows that the triple point of carbon dioxide is at a pressure well above 1 atm, meaning liquid carbon dioxide cannot exist at normal pressures. At 1 atm pressure, solid carbon dioxide, often referred to as dry ice, bypasses the liquid phase entirely and sublimes at −78.5°C, which is the substance's normal sublimation temperature. This process is the result of the unique properties of CO2 as depicted on its phase diagram.