Question

phase diagram
pressure (atmospheres)
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0.00
-200 -100 0 100 200 300 400 500 600 700 800 900
temperature (degrees c)
at 1.5 atm and 400°c, the substance is...
a melting
b boiling
c gas
d solid
e liquid
part d
what is the freezing point at stp?
a 800°c
b 500°c
c 350°c
d 100°c
part e
what is the melting point at stp?
a 350°c
b 500°c

Explanation:

Part (Question about substance state at 1.5 atm and 400°C)

To determine the state, analyze the phase diagram. Locate 1.5 atm (y - axis) and 400°C (x - axis). The region at these conditions (above the liquid - gas and solid - liquid lines) corresponds to gas? Wait, no, let's re - examine. Wait, the phase diagram: the left line is solid - liquid, the right is liquid - gas. At 1.5 atm (pressure) and 400°C (temperature), we check the regions. Wait, maybe I made a mistake. Wait, the pressure is 1.5 atm, temperature 400°C. Looking at the diagram, the liquid - gas line (vapor pressure curve) and solid - liquid line. Wait, actually, at 1.5 atm (which is above 1 atm) and 400°C, the substance is in gas phase? Wait, no, maybe the correct option is C (Gas)? Wait, no, let's think again. Wait, the phase diagram: the two lines meet at a triple point? Wait, the left line (steeper) is solid - liquid equilibrium, the right (shallower) is liquid - gas. At 1.5 atm (y = 1.5) and x = 400, we are in the gas region? Wait, maybe. But let's check the options. The options are Melting (A), Boiling (B), Gas (C), Solid (D), Liquid (E). At 1.5 atm and 400°C, the substance is gas? So option C.

STP pressure is 1 atm (1.00 atm). On the phase diagram, find the solid - liquid equilibrium line (the steeper line) at pressure = 1 atm (y - axis). The intersection with this line on the x - axis (temperature) is the freezing point. Looking at the diagram, at y = 1.00 (1 atm), the x - value (temperature) is 100°C? Wait, no, wait the x - axis is temperature (°C). Wait, the solid - liquid line: when pressure is 1 atm, the temperature at the solid - liquid equilibrium (freezing point) is where? Wait, the diagram: the left line (solid - liquid) and the right line (liquid - gas). At STP (1 atm), the freezing point is the temperature at which solid and liquid coexist, so we look at the solid - liquid line at P = 1 atm. From the diagram, when P = 1 atm (y = 1.00), the x (temperature) is 100°C? Wait, but that seems high. Wait, maybe the correct option is D (100°C).

Melting point at STP (1 atm) is the same as freezing point (since melting and freezing are reverse processes at the same temperature and pressure). So at STP (1 atm), the melting point is the temperature at solid - liquid equilibrium, which we determined in Part D as 100°C? But the options are A (350°C) and B (500°C). Wait, maybe I misread the diagram. Wait, the solid - liquid line: let's re - examine the diagram. The two lines: the left (steeper) line and the right (shallower) line. The triple point? Wait, maybe the solid - liquid line at 1 atm: looking at the x - axis, when P = 1 atm, the temperature is 100°C? But the options for Part E are 350°C and 500°C. Wait, maybe I made a mistake. Wait, maybe the STP here is not 1 atm? No, STP is 1 atm and 0°C, but in the context of the phase diagram, maybe the pressure is 1 atm. Wait, maybe the solid - liquid line at 1 atm has a temperature of 100°C, but the options for Part E are 350 and 500. Wait, maybe the diagram's x - axis is misread. Wait, the x - axis is from - 200 to 900. Wait, maybe the solid - liquid line at 1 atm is at 100°C, but the options for Part E are different. Wait, maybe the question is about melting point at STP, and the correct option is A (350°C)? No, this is confusing. Wait, maybe the initial analysis was wrong. Let's start over.

For Part D: Freezing point at STP (1 atm). The solid - liquid equilibrium line: find P = 1 atm (y = 1.00) on the y - axis, then find the x - value (temperature) where the solid - liquid line is. From the diagram, the solid - liquid line (steeper) and liquid - gas line (shallower) meet at a point. Then, at P = 1 atm, the temperature for solid - liquid equilibrium (freezing point) is, looking at the x - axis, maybe 100°C (option D). For Part E, melting point at STP is the same as freezing point, but the options are 350 and 500. Wait, maybe the diagram is different. Wait, maybe the solid - liquid line at 1 atm is at 100°C, but the options for Part E are wrong? No, maybe I misread the lines. Alternatively, maybe the "STP" here is different, but no, STP is 1 atm. Wait, perhaps the correct answer for Part E is A (350°C)? No, this is unclear. Wait, maybe the original diagram has the solid - liquid line at 1 atm corresponding to 100°C for freezing (Part D, option D) and melting (Part E, but the options are 350 and 500, which is a contradiction). Maybe there's a mistake in the problem, but based on the options, for Part D, the answer is D (100°C), and for Part E, if melting point is same as freezing point, but the options don't have 100, so maybe I made a mistake. Wait, maybe the solid - liquid line is at a higher temperature. Wait, the x - axis: 0, 100, 200, 300, 400, 500, etc. The solid - liquid line (steeper) goes from (0, 0) to (100, 0.75) to (200, 2.00)? No, the diagram shows pressure on y - axis (atm) and temperature on x - axis (°C). The left line (steeper) starts at (0, 0) and goes up, the right line (shallower) starts at (0, 0) and goes up. Wait, maybe the triple point is at (0, 0). Then, at P = 1 atm (y = 1.00), the solid - liquid line is at x = 100°C (so freezing point 100°C, Part D option D), and melting point is also 100°C, but Part E options are 350 and 500. This is a problem. Maybe the diagram is different. Alternatively, maybe the "STP" here is not 1 atm, but that's non - standard. Given the options, for Part D, the answer is D (100°C), and for Part E, maybe the intended answer is A (350°C) or B (500°C), but based on the diagram as per the given image, the freezing point at 1 atm is 100°C (Part D, option D), and melting point is same,…

Answer:

C. Gas

Part D (Freezing point at STP)