Consider the phase diagram for iodine shown at the top of the next page. a. What is the normal boiling point for iodine? b. What is the melting point for iodine at 1 atm? c. Which state is present at room temperature and normal atmospheric pressure? d. Which state is present at 186 C and 1.0 atm?
The correct answer and explanation is:
To accurately answer the questions based on the phase diagram of iodine, we will interpret common characteristics of iodine’s phase behavior. Here’s a detailed explanation for each part:
a. What is the normal boiling point for iodine?
Answer: 184°C
Explanation:
The normal boiling point of a substance is the temperature at which it changes from liquid to gas (boils) at 1 atmosphere (atm) of pressure. For iodine (I₂), this occurs at approximately 184°C. On a phase diagram, this point is located where the liquid-gas boundary line intersects the 1 atm line. At this temperature, the vapor pressure of iodine equals atmospheric pressure, allowing it to transition to a gaseous state.
b. What is the melting point for iodine at 1 atm?
Answer: 114°C
Explanation:
The melting point is the temperature at which a substance transitions from solid to liquid at a given pressure—here, 1 atm. According to iodine’s phase diagram, this occurs at around 114°C. At this temperature and pressure, solid iodine absorbs heat and becomes liquid without a change in pressure.
c. Which state is present at room temperature and normal atmospheric pressure?
Answer: Solid
Explanation:
Room temperature is typically around 25°C (77°F), and normal atmospheric pressure is 1 atm. On the iodine phase diagram, this condition falls within the solid region. Therefore, under these conditions, iodine exists as a solid. Notably, iodine is one of the few solids that can sublime, meaning it can transition directly to gas under certain conditions without becoming liquid first—but at room temperature and 1 atm, it stays solid.
d. Which state is present at 186°C and 1.0 atm?
Answer: Gas
Explanation:
At 186°C and 1 atm, iodine is above its normal boiling point (184°C). This places it in the gaseous region of the phase diagram. Therefore, under these conditions, iodine exists as a gas, having already transitioned from liquid to vapor.
Summary Table:
| Question | Answer |
|---|---|
| a | 184°C |
| b | 114°C |
| c | Solid |
| d | Gas |
Each of these answers depends on interpreting the boundaries in a phase diagram, which shows regions of stability for solid, liquid, and gas phases based on temperature and pressure.