Ch.11 - Liquids and Intermolecular Forces

Problem 5a

Chapter 11, Problem 5a

Using this graph of CS2 data, determine (a) the approximate vapor pressure of CS2 at 30°C,

Verified step by step guidance

Step 1: Locate the point on the graph that corresponds to a temperature of 30°C. This will be along the x-axis (horizontal axis) of the graph, which typically represents temperature in a vapor pressure graph.

Step 2: From the point at 30°C, draw a line straight up until it intersects with the curve representing the vapor pressure of CS2.

Step 3: Once your line intersects with the curve, draw a line horizontally from that point to the y-axis (vertical axis), which typically represents vapor pressure in a vapor pressure graph.

Step 4: The point where your horizontal line intersects with the y-axis is the approximate vapor pressure of CS2 at 30°C.

Step 5: Read off the value from the y-axis. This is your approximate vapor pressure of CS2 at 30°C. Remember, this is an approximation based on the graph and may not be the exact value.

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Key Concepts

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

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. It reflects the tendency of particles to escape from the liquid phase into the vapor phase. Higher temperatures generally increase vapor pressure, as more molecules have sufficient energy to overcome intermolecular forces.

Phase Equilibrium

Phase equilibrium occurs when the rates of the forward and reverse processes of a phase change are equal, resulting in no net change in the amount of each phase. In the context of vapor pressure, this means that the number of molecules evaporating from the liquid equals the number condensing back into it, allowing for a stable vapor pressure at a specific temperature.

Temperature Dependence of Vapor Pressure

The vapor pressure of a substance is highly dependent on temperature, typically increasing as temperature rises. This relationship is often described by the Clausius-Clapeyron equation, which relates the change in vapor pressure with temperature to the enthalpy of vaporization. Understanding this concept is crucial for interpreting vapor pressure data at different temperatures.

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Related Practice

Textbook Question

(a) Which kind of intermolecular attractive force is shown in each case here? (b) Predict which of the four interactions is the weakest. [Section 11.2]

Carbon tetrachloride, CCl4, and chloroform, CHCl3, are common organic liquids. Carbon tetrachloride’s normal boiling point is 77 °C; chloroform’s normal boiling point is 61 °C. Which statement is the best explanation of these data? (a) Chloroform can hydrogen-bond, but carbon tetrachloride cannot. (b) Carbon tetrachloride has a larger dipole moment than chloroform. (c) Carbon tetrachloride is more polarizable than chloroform.

Textbook Question

If 42.0 kJ of heat is added to a 32.0-g sample of liquid meth-ane under 1 atm of pressure at a temperature of -170°C, what are the final state and temperature of the methane once the system equilibrates? Assume no heat is lost to the surroundings. The normal boiling point of methane is -161.5 °C. The specific heats of liquid and gaseous methane are 3.48 and 2.22 J/g-K, respectively. [Section 11.3]

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Textbook Question

The molecules

have the same molecular formula (C3H8O) but different chemical structures. (b) Which molecule do you expect to have a larger dipole moment? [Sections 11.2 and 11.5]

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Textbook Question

The phase diagram of a hypothetical substance is

(b) What is the physical state of the substance under the following conditions? (i) T = 150 K, P = 0.2 atm; (ii) T = 100 K, P = 0.8 atm; (iii) T = 300K, P = 1.0atm. [Section 11.6]

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Textbook Question

At three different temperatures, T1, T2, and T3, the molecules in a liquid crystal align in these ways:

(a) At which temperature or temperatures is the substance in a liquid crystalline state? At those temperatures, which type of liquid crystalline phase is depicted?

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