Below is the phase diagram for iodine. What state is present at room temperature (i.e., 25.0 C) and normal atmospheric pressure (i.e., 1 atm)?
a) solid
b) liquid
c) gas
d) All three states exist at room temperature and 1 atm
e) none of these
The Correct Answer and Explanation is:
Correct Answer: a) solid
Explanation:
To determine the physical state of iodine at room temperature and 1 atmosphere of pressure, we must analyze the phase diagram of iodine, a graphical representation showing the physical states of a substance under various conditions of temperature and pressure.
Step 1: Understand the Axes of the Phase Diagram
- The x-axis represents temperature, usually in degrees Celsius.
- The y-axis represents pressure, typically in atmospheres (atm) or Pascals (Pa).
- The diagram is divided into regions that correspond to the solid, liquid, and gas phases of the substance.
- Lines (boundaries) between these regions indicate the conditions at which two phases coexist in equilibrium (such as melting, boiling, or sublimation points).
Step 2: Identify Room Temperature and Normal Pressure
- Room temperature is 25.0°C
- Normal atmospheric pressure is 1 atm
- Locate the point (25.0°C, 1 atm) on the phase diagram.
Step 3: Analyze the Position of the Point
For iodine, the key points are:
- Sublimation point: Iodine sublimates (goes from solid directly to gas) at about 113.7°C at 1 atm.
- Melting point (solid to liquid): Around 113.7°C at higher pressures.
- Boiling point (liquid to gas): About 184.3°C at 1 atm.
At 1 atm and 25.0°C, the point lies well below the melting point and boiling point, and it is located in the solid region of the phase diagram.
Step 4: Conclusion
Since 25.0°C and 1 atm fall into the solid region on iodine’s phase diagram, iodine exists as a solid under these conditions.
It’s also interesting to note that although iodine is a solid, it can slowly sublimate (turn directly into a purple vapor) at room temperature, giving off a visible violet gas. However, this does not mean it is in the gas phase at 1 atm—it simply means it has a high vapor pressure.
Final Answer: a) solid
