Q: How much energy (in kJ) is required to convert 3.25 mol of ethanol from liquid to gas at 78.3 °C? ($$\Delta H_{vap}$$ for ethanol = 39.3 kJ/mol)

$$3.25 \times 39.3 = 127.725 kJ$$

Q: How much energy (in kJ) is required to convert 25.0 g of H$$_2O $$from ice to water at 0 °C? ($$\Delta H_{fus}$$ for water = 6.01 kJ/mol, molar mass of H$$_2O = 18.02 g/$$mol)

$$\frac{25.0}{18.02} \times 6.01 = 8.34 kJ$$

Q: How much energy (in kJ) is required to convert 0.342 mol of benzene from solid to liquid at 5.5 °C? ($$\Delta H_{fus}$$ for benzene = 10.9 kJ/mol)

$$0.342 \times 10.9 = 3.73 kJ$$

Question 1

Which intermolecular force is the strongest in HF molecules?

Accepted Answer

Hydrogen bonding

Question 2

What type of intermolecular forces exist between CO$$_2$$ molecules?

Accepted Answer

Dispersion forces only

Question 3

Which intermolecular force is present between SO$$_2$$ and water?

Accepted Answer

Dipole-dipole forces

Question 4

Rank the noble gases from lowest to highest boiling point.

Accepted Answer

Ne \u003c Ar \u003c Kr \u003c Xe

Question 5

Which compound has the highest boiling point: MgCl$$_2$$, H$$_2O$$, O$$_2$$, CH$$_2F$_2$$?

Accepted Answer

MgCl$$_2$$

Question 6

How much energy (in kJ) is required to convert 3.25 mol of ethanol from liquid to gas at 78.3 °C? ($$\Delta H_{vap}$$ for ethanol = 39.3 kJ/mol)

Accepted Answer

$$3.25 	imes 39.3 = 127.725 kJ$$

Question 7

How much energy (in kJ) is required to convert 25.0 g of H$$_2O $$from ice to water at 0 °C? ($$\Delta H_{fus}$$ for water = 6.01 kJ/mol, molar mass of H$$_2O = 18.02 g/$$mol)

Accepted Answer

$$\frac{25.0}{18.02} 	imes 6.01 = 8.34 kJ$$

Question 8

How much energy (in kJ) is required to convert 32.0 g of water at 45 °C to steam at 123 °C? (specific heat of water: 4.18 J/g°C, specific heat of steam: 1.99 J/g°C, $$\Delta H_{vap} = 40.79 kJ/$$mol, molar mass = 18.02 g/mol)

Accepted Answer

Total energy = $$Q_1$$ + $$Q_2$$ + $$Q_3$$ where $$Q_1 = 32.0$$ 	imes 4.18 	imes (100-45)$$, Q_2$ = \frac{32.0}{18.02} 	imes 40.79$$, $$Q_3 = 32.0$$ 	imes 1.99 	imes (123-100)$$; Total = 9.2 kJ + 72.5 kJ + 1.46 kJ = 83.16 kJ

Question 9

On a heating curve, why is the horizontal line at segment 4 longer than the horizontal line at segment 2?

Accepted Answer

Because more energy is required for vaporization than for fusion

Question 10

Which intermolecular forces are present between CH$$_4$$ and hexane (C$$_6H$_{14}$$)?

Accepted Answer

Dispersion forces

Question 11

What phase change is represented by arrow Z in the phase diagram?

Accepted Answer

Condensation

Question 12

At point D in the phase diagram, what state of matter is present?

Accepted Answer

Liquid

Question 13

Which of the following best explains why the line at segment 5 of a heating curve is steeper than the line at segment 3?

Accepted Answer

The specific heat of the gas is lower than that of the liquid

Question 14

Which intermolecular force is the strongest in NH$$_3$$ molecules?

Accepted Answer

Hydrogen bonding

Question 15

What phase change is represented by arrow Y in the phase diagram?

Accepted Answer

Sublimation

Question 16

Which intermolecular forces are present between MgCl$$_2$$ and water?

Accepted Answer

Ion-dipole forces

Question 17

How much energy (in kJ) is required to convert 0.342 mol of benzene from solid to liquid at 5.5 °C? ($$\Delta H_{fus}$$ for benzene = 10.9 kJ/mol)

Accepted Answer

$$0.342 	imes 10.9 = 3.73 kJ$$

Intermolecular Forces, Phase Changes, and Energy Calculations – General Chemistry Study Guide

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