Ch.11 - Liquids and Intermolecular Forces

Problem 62a

Chapter 11, Problem 62a

Referring to Figure 11.29, describe the phase changes (and the temperatures at which they occur) when CO2 is heated from -80 to -20°C at (a) a constant pressure of 3 atm,

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Identify the phase diagram for CO2, which shows the phases (solid, liquid, gas) and the lines representing phase changes at different pressures and temperatures.

Locate the pressure of 3 atm on the phase diagram. This will help determine the phase changes CO2 undergoes as it is heated.

Trace a horizontal line at 3 atm from -80°C to -20°C on the phase diagram to observe the phase changes.

Note the temperatures at which the line crosses the phase boundaries. These are the temperatures at which phase changes occur.

Describe the phase changes: starting from solid CO2 (dry ice) at -80°C, identify if it sublimates directly to gas or if it passes through a liquid phase, based on the phase diagram at 3 atm.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Phase Changes

Phase changes refer to the transitions between different states of matter, such as solid, liquid, and gas. In the context of CO2, these changes include sublimation (solid to gas) and deposition (gas to solid). Understanding these transitions is crucial for analyzing how CO2 behaves under varying temperature and pressure conditions.

Phase Diagrams

A phase diagram is a graphical representation that shows the phases of a substance at different temperatures and pressures. It helps predict the state of a substance under specific conditions. For CO2, the phase diagram indicates the boundaries between solid, liquid, and gas phases, which are essential for determining the phase changes occurring at 3 atm pressure.

Critical Point

The critical point is the temperature and pressure at which the distinction between liquid and gas phases disappears. For CO2, this point is significant because it defines the conditions under which CO2 can exist as a supercritical fluid. Understanding the critical point is important for predicting the behavior of CO2 when heated from -80 to -20°C at a constant pressure of 3 atm.

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Textbook Question

You are high up in the mountains and boil water to make some tea. However, when you drink your tea, it is not as hot as it should be. You try again and again, but the water is just not hot enough to make a hot cup of tea. Which is the best explanation for this result? (a) High in the mountains, it is probably very dry, and so the water is rapidly evaporating from your cup and cooling it. (b) High in the mountains, it is probably very windy, and so the water is rapidly evaporating from your cup and cooling it. (c) High in the mountains, the air pressure is significantly less than 1 atm, so the boiling point of water is much lower than at sea level. (d) High in the mountains, the air pressure is significantly less than 1 atm, so the boiling point of water is much higher than at sea level.

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Textbook Question

Using the vapor-pressure curves in Figure 11.24, (d) estimate the external pressure at which diethyl ether will boil at 40 °C.

Textbook Question

Appendix B lists the vapor pressure of water at various external pressures. (c) A city at an altitude of 5000 ft above sea level has a barometric pressure of 633 torr. To what temperature would you have to heat water to boil it in this city?

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Textbook Question

The phase diagram for neon is

Use the phase diagram to answer the following questions. (a) What is the approximate value of the normal melting point?

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Textbook Question

Use the phase diagram of neon to answer the following questions. (a) What is the approximate value of the normal boiling point?

Textbook Question

Use the phase diagram of neon to answer the following questions. (b) What can you say about the strength of the intermolecular forces in neon and argon based on the critical points of Ne and Ar (see Table 11.5.)?

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