Q: How much energy (J) is required to convert 55.8 g of ice at -5 ºC to water vapor at 100 ºC? Use the following values: Specific heat of ice $c = 2.09 \frac{J}{g\cdot ^\circ C}$, $\Delta H_{fusion} = 334 \frac{J}{g}$, Specific heat of water $c = 4.184 \frac{J}{g\cdot ^\circ C}$, $\Delta H_{vaporization} = 2260 \frac{J}{g}$.

Total energy = $55.8 \times 2.09 \times 5 + 55.8 \times 334 + 55.8 \times 4.184 \times 100 + 55.8 \times 2260 = 55.8 \times (10.45 + 334 + 418.4 + 2260) = 55.8 \times 3023.85 = 168,799$ J

Q: A plot of $\ln P$ vs $\frac{1}{T}$ for a liquid yields a straight line with a slope of $-2.79 \times 10^3$ K. What is the enthalpy of vaporization ($\Delta H_{vap}$) for this liquid? (Use $R = 8.314 \frac{J}{mol\cdot K}$)

$\Delta H_{vap} = -\text{slope} \times R = -2.79 \times 10^3 \times 8.314 = 23,180$ J/mol

Question 1

Which of the following best describes a nonpolar molecule?

Accepted Answer

A molecule with a symmetrical shape and no lone pairs on the central atom.

Question 2

Which intermolecular force is present in all types of compounds?

Accepted Answer

London dispersion forces

Question 3

What is the dominant intermolecular force between magnesium sulfate (Epsom salts) and water?

Accepted Answer

Ion-dipole forces

Question 4

Which of the following molecules is expected to have the largest dispersion forces?

Accepted Answer

C12H26

Question 5

A heating curve for water shows several segments. Which segment corresponds to the calculation $q = mc\Delta T$ for liquid water?

Accepted Answer

C - D

Question 6

How much energy (J) is required to convert 55.8 g of ice at -5 ºC to water vapor at 100 ºC? Use the following values: Specific heat of ice $c = 2.09 \frac{J}{g\cdot ^\circ C}$, $\Delta H_{fusion} = 334 \frac{J}{g}$, Specific heat of water $c = 4.184 \frac{J}{g\cdot ^\circ C}$, $\Delta H_{vaporization} = 2260 \frac{J}{g}$.

Accepted Answer

Total energy = $55.8 	imes 2.09 	imes 5 + 55.8 	imes 334 + 55.8 	imes 4.184 	imes 100 + 55.8 	imes 2260 = 55.8 	imes (10.45 + 334 + 418.4 + 2260) = 55.8 	imes 3023.85 = 168,799$ J

Question 7

Which of the following compounds would have the highest melting point?

Accepted Answer

CaS in H2O

Question 8

Which of the following will have the lowest boiling point?

Accepted Answer

C6H14

Question 9

Which molecules would most likely cause a liquid to have the lowest viscosity?

Accepted Answer

Small, nonpolar molecules

Question 10

Which of the following should have the highest surface tension at a given temperature?

Accepted Answer

CI4

Question 11

On a phase diagram, what is the triple point?

Accepted Answer

The unique set of conditions where all three states of matter are stable and in equilibrium.

Question 12

At what temperature can we no longer tell the difference between the liquid and gas phases?

Accepted Answer

820 ºC

Question 13

Which segment of a heating curve represents a phase change where temperature remains constant?

Accepted Answer

D - E

Question 14

The Clausius-Clapeyron equation relates which two properties?

Accepted Answer

Vapor pressure and temperature

Question 15

Given the linear form of the Clausius-Clapeyron equation $\ln P = \frac{-\Delta H_{vap}}{R} \frac{1}{T} + C$, what does the slope of a plot of $\ln P$ vs $\frac{1}{T}$ represent?

Accepted Answer

The negative enthalpy of vaporization divided by the gas constant, $-\frac{\Delta H_{vap}}{R}$

Question 16

Benzene has a heat of vaporization of 30.72 kJ/mol and a normal boiling point of 80.1°C. At what temperature does benzene boil when the external pressure is 405 torr? (Use the two-point Clausius-Clapeyron equation: $\ln \frac{P_2}{P_1} = \frac{\Delta H_{vap}}{R} \left( \frac{1}{T_1} - \frac{1}{T_2} \right)$)

Accepted Answer

333.2 K

Question 17

Which of the following best describes the relationship between intermolecular forces and boiling point?

Accepted Answer

Stronger intermolecular forces result in a higher boiling point.

Question 18

A plot of $\ln P$ vs $\frac{1}{T}$ for a liquid yields a straight line with a slope of $-2.79 	imes 10^3$ K. What is the enthalpy of vaporization ($\Delta H_{vap}$) for this liquid? (Use $R = 8.314 \frac{J}{mol\cdot K}$)

Accepted Answer

$\Delta H_{vap} = -	ext{slope} 	imes R = -2.79 	imes 10^3 	imes 8.314 = 23,180$ J/mol

Liquids, Solids, and Intermolecular Forces: Structured Study Notes

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