11.55 Using the vapor-pressure curves in Figure 11.25, (a) estimate the boiling point of ethanol at an external pressure of 200 torr, (b) estimate the external pressure at which ethanol will boil at 60 °C, (c) estimate the boiling point of diethyl ether at 400 torr, (d) estimate the external pressure at which diethyl ether will boil at 40 °C. 11 F Go Figure Volatility, Vapor Pressure, and Temperature When vaporization occurs in an open container, as when water evaporates from a bowl, the vapor moves away from the liquid. Little, if any, is recaptured at the surface of the liquid. Equilibrium What is the vapor pressure of ethylene glycol at its normal boiling point? ture where COr never occurs, and the continues to form until the liquid evap gas ization Pvers Using subs orates to dryness. Substances with high vapor pressure (such as vapor gasoline) evaporate more quickly than substances with low vapor 34.6 °C 800 760 78.3 °C 100 °C pressure (such as motor oil). Liquids that evaporate readily are said to be volatile. Normal boiling point Hot water evaporates more quickly than cold water because vapor pressure increases with increasing temperature. To see why this statement is true, we begin with the fact that the molecules of a liquid move at various speeds. Figure 11.24 shows the distribution of kinetic energies of the molecules at the surface of a liquid at two tem- peratures. (The curves are like those shown for gases in Section 10.7) As the temperature is increased, the molecules move more energeti- cally and more of them can break free from their neighbors and enter the gas phase, increasing the vapor pressure. Figure 11.25 depicts the variation in vapor pressure with tem- perature for four common substances that differ greatly in volatility. Note that the vapor pressure in all cases increases nonlinearly with increasing temperature. The weaker the intermolecular forces in the liquid, the more easily molecules can escape and, therefore, the higher the vapor pressure at a given temperature. 600 Diethyl ether tic Ethyl alcohol (ethanol) ga 400 Water 200 Ethylene glycol 0 0 20 40 60 80 100 Temperature (C) Figure 11.25 Vapor pressure for four liquids as a function of mperature. I I Vapor pressure (torr)

Chemistry for Engineering Students
4th Edition
ISBN:9781337398909
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Chapter8: Molecules And Materials
Section: Chapter Questions
Problem 8.87PAE: 8.87 Use the vapor pressure curves illustrated here to answer the questions that follow. (a) What is...
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11.55 Using the vapor-pressure curves in Figure 11.25, (a) estimate
the boiling point of ethanol at an external pressure of 200
torr, (b) estimate the external pressure at which ethanol
will boil at 60 °C, (c) estimate the boiling point of diethyl
ether at 400 torr, (d) estimate the external pressure at which
diethyl ether will boil at 40 °C.
11 F
Transcribed Image Text:11.55 Using the vapor-pressure curves in Figure 11.25, (a) estimate the boiling point of ethanol at an external pressure of 200 torr, (b) estimate the external pressure at which ethanol will boil at 60 °C, (c) estimate the boiling point of diethyl ether at 400 torr, (d) estimate the external pressure at which diethyl ether will boil at 40 °C. 11 F
Go Figure
Volatility, Vapor Pressure, and Temperature
When vaporization occurs in an open container, as when water
evaporates from a bowl, the vapor moves away from the liquid.
Little, if any, is recaptured at the surface of the liquid. Equilibrium
What is the vapor pressure of ethylene glycol at its
normal boiling point?
ture
where
COr
never occurs, and the
continues to form until the liquid evap
gas
ization
Pvers
Using
subs
orates to dryness. Substances with high vapor pressure (such as
vapor
gasoline) evaporate more quickly than substances with low vapor
34.6 °C
800
760
78.3 °C
100 °C
pressure (such as motor oil). Liquids that evaporate readily are said
to be volatile.
Normal boiling
point
Hot water evaporates more quickly than cold water because
vapor pressure increases with increasing temperature. To see why
this statement is true, we begin with the fact that the molecules of a
liquid move at various speeds. Figure 11.24 shows the distribution of
kinetic energies of the molecules at the surface of a liquid at two tem-
peratures. (The curves are like those shown for gases in Section 10.7)
As the temperature is increased, the molecules move more energeti-
cally and more of them can break free from their neighbors and enter
the gas phase, increasing the vapor pressure.
Figure 11.25 depicts the variation in vapor pressure with tem-
perature for four common substances that differ greatly in volatility.
Note that the vapor pressure in all cases increases nonlinearly with
increasing temperature. The weaker the intermolecular forces in
the liquid, the more easily molecules can escape and, therefore, the
higher the vapor pressure at a given temperature.
600
Diethyl
ether
tic
Ethyl alcohol
(ethanol)
ga
400
Water
200
Ethylene
glycol
0
0
20
40
60
80
100
Temperature (C)
Figure 11.25 Vapor pressure for four liquids as a function of
mperature.
I
I
Vapor pressure (torr)
Transcribed Image Text:Go Figure Volatility, Vapor Pressure, and Temperature When vaporization occurs in an open container, as when water evaporates from a bowl, the vapor moves away from the liquid. Little, if any, is recaptured at the surface of the liquid. Equilibrium What is the vapor pressure of ethylene glycol at its normal boiling point? ture where COr never occurs, and the continues to form until the liquid evap gas ization Pvers Using subs orates to dryness. Substances with high vapor pressure (such as vapor gasoline) evaporate more quickly than substances with low vapor 34.6 °C 800 760 78.3 °C 100 °C pressure (such as motor oil). Liquids that evaporate readily are said to be volatile. Normal boiling point Hot water evaporates more quickly than cold water because vapor pressure increases with increasing temperature. To see why this statement is true, we begin with the fact that the molecules of a liquid move at various speeds. Figure 11.24 shows the distribution of kinetic energies of the molecules at the surface of a liquid at two tem- peratures. (The curves are like those shown for gases in Section 10.7) As the temperature is increased, the molecules move more energeti- cally and more of them can break free from their neighbors and enter the gas phase, increasing the vapor pressure. Figure 11.25 depicts the variation in vapor pressure with tem- perature for four common substances that differ greatly in volatility. Note that the vapor pressure in all cases increases nonlinearly with increasing temperature. The weaker the intermolecular forces in the liquid, the more easily molecules can escape and, therefore, the higher the vapor pressure at a given temperature. 600 Diethyl ether tic Ethyl alcohol (ethanol) ga 400 Water 200 Ethylene glycol 0 0 20 40 60 80 100 Temperature (C) Figure 11.25 Vapor pressure for four liquids as a function of mperature. I I Vapor pressure (torr)
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