Q: Calculate the amount of heat (in kJ) required to vaporize 100 g of water at its boiling point. (Heat of vaporization of water at 100 ºC is $$40.7\ \text{kJ/mol}$$, molar mass of water is $$18.02\ \text{g/mol})$$

$$\frac{100\ \text{g}}{18.02\ \text{g/mol}} \times 40.7\ \text{kJ/mol} = 226\ \text{kJ}$$

Q: A sample of ice at 0 ºC absorbs 120 kJ of heat. How many grams of ice melt? (Heat of fusion for water is $$6.02\ \text{kJ/mol}$$, molar mass of water is $$18.02\ \text{g/mol})$$

$$\frac{120\ \text{kJ}}{6.02\ \text{kJ/mol}} \times 18.02\ \text{g/mol} = 359\ \text{g}$$

Question 1

Which of the following best explains why water is a liquid at room temperature despite its low molar mass?

Accepted Answer

Water molecules are held together by strong hydrogen bonds.

Question 2

A fly-fishing lure floats on water even though it is denser than water. Which property of water is responsible for this phenomenon?

Accepted Answer

Surface tension

Question 3

Which intermolecular force is present in all molecules and atoms, regardless of their polarity?

Accepted Answer

Dispersion force

Question 4

Which of the following statements about evaporation is correct?

Accepted Answer

Evaporation is an endothermic process because energy is required to break intermolecular forces.

Question 5

Calculate the amount of heat (in kJ) required to vaporize 100 g of water at its boiling point. (Heat of vaporization of water at 100 ºC is $$40.7\ 	ext{kJ/mol}$$, molar mass of water is $$18.02\ 	ext{g/mol})$$

Accepted Answer

$$\frac{100\ 	ext{g}}{18.02\ 	ext{g/mol}} 	imes 40.7\ 	ext{kJ/mol} = 226\ 	ext{kJ}$$

Question 6

Which of the following best describes the difference between solids and liquids at the molecular level?

Accepted Answer

In solids, molecules are fixed in position and only vibrate; in liquids, molecules are free to move around each other.

Question 7

Which intermolecular force is responsible for the high boiling point of hydrogen fluoride (HF)?

Accepted Answer

Hydrogen bonding

Question 8

A sample of ice at 0 ºC absorbs 120 kJ of heat. How many grams of ice melt? (Heat of fusion for water is $$6.02\ 	ext{kJ/mol}$$, molar mass of water is $$18.02\ 	ext{g/mol})$$

Accepted Answer

$$\frac{120\ 	ext{kJ}}{6.02\ 	ext{kJ/mol}} 	imes 18.02\ 	ext{g/mol} = 359\ 	ext{g}$$

Question 9

Which of the following is NOT a property of liquids?

Accepted Answer

Liquids have indefinite volume and are easily compressed.

Question 10

Which type of crystalline solid is composed of formula units held together by electrostatic attractions?

Accepted Answer

Ionic solid

Question 11

Why does ice float on water?

Accepted Answer

Ice is less dense than liquid water because water expands upon freezing.

Question 12

Which intermolecular force is strongest among the following?

Accepted Answer

Ion–dipole force

Question 13

Which process is exothermic?

Accepted Answer

Condensation

Question 14

Which of the following best describes the effect of increasing temperature on vapor pressure?

Accepted Answer

Vapor pressure increases with increasing temperature.

Question 15

Which of the following is a manifestation of intermolecular forces in liquids?

Accepted Answer

Surface tension and viscosity

Question 16

Which of the following statements about the heat of fusion is correct?

Accepted Answer

The heat of fusion is the amount of heat required to melt 1 mole of a solid.

Question 17

Which of the following would have the highest boiling point?

Accepted Answer

A polar molecule with hydrogen bonding

Question 18

Which of the following is an example of a molecular solid?

Accepted Answer

Dry ice (CO$$_2)$$

Question 19

Which intermolecular force is responsible for the miscibility of water and ethanol?

Accepted Answer

Hydrogen bonding

Question 20

Which of the following best explains why oily stains cannot be washed away with plain water?

Accepted Answer

Water is polar and oil is nonpolar, so they are not miscible.

Liquids, Solids, and Intermolecular Forces: Structured Study Notes

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