CHEM125 – CHAPTER 11 – BASIC HOMEWORK

CHAPTER 11 BASIC HOMEWORK

Resources:

Have you found videos, websites, or explanations that helped you understand this chapter? Let us know and we’ll add them to “Resources” part of this page for other students to use.

Answer Explanations Coming Soon!

Question 1

Correctly match the properties.

Help: Energy of attraction

Water at -50oCAnswer 1Choose…molecular kinetic energy is much less than energy of attraction between moleculesmolecular kinetic energy about equal to energy of attraction between moleculesmolecular kinetic energy >> energy of attraction between molecules Correct
Water at 50oCAnswer 2Choose…molecular kinetic energy is much less than energy of attraction between moleculesmolecular kinetic energy about equal to energy of attraction between moleculesmolecular kinetic energy >> energy of attraction between molecules Correct
Water at 150oCAnswer 3Choose…molecular kinetic energy is much less than energy of attraction between moleculesmolecular kinetic energy about equal to energy of attraction between moleculesmolecular kinetic energy >> energy of attraction between molecules Correct

Explanation

At below freezing point the kinetic energy of molecules is very minimum. At 50 C the kinetic energy of molecules is equal to the attraction of the molecules. At 120 C the kinetic energy of molecules is greater than the attraction of the molecules.

Question 2

Which of the following molecules have dipole-dipole forces between different molecules? (The question is equivalent to asking which of the following molecules are polar molecules. Lewis structures may need to be drawn.)

Select one or more:a. Cl2b. HCl Correctc. BF3d. BI2Cl Correcte. PH3 Correct

Explanation

Dipole–dipole force exists between all molecules that are polar. Polar molecules have electron-rich regions (which have a partial negative charge) and electron-deficient regions (which have a partial positive charge).

Question 3

Which of the following molecules have H-bonding and thus a higher than expected melting and boiling point?

Help: Hydrogen bonding

Select one or more:a. H2b. HClc. HF Correctd. H2O Correcte. CH2O (both H bonded to C)f. CH3OH Correct

Explanation

H bonds occur between with only these elements F, O, N

Question 4

For each of the following molecules pick the one with the greater London forces and hence higher melting and boiling point?

Help: London forces

Select one or more: a. London forces greater for Cl2 than I2b. London forces greater for I2 than Cl2 Correctc. London forces greater for Cl2 than F2 Correctd. London forces greater for F2 than Cl2e. London forces greater for PH3 than AsH3f. London forces greater for AsH3 than PH3 Correctg. London forces greater for C4H10 than C5H12h. London forces greater for C5H12 than C4H10 Correct

Explanation

Dispersion forces are the result of fluctuations in the electron distribution within molecules or atoms. CHEM125 - CHAPTER 11 - BASIC HOMEWORK 1

Question 5

What is the greatest contribution to the energy of interaction between different water molecules.

Help: Energy of interaction

Select one:a. Hydrogen bonding Correctb. London energy, but hydrogen bonding still importantc. London energyd. Dipole-dipole energy

Explanation

Hydrogen Bonding is the strongest among dispersion (London) , dipoles forces. CHEM125 - CHAPTER 11 - BASIC HOMEWORK 2

Question 6

What is the greatest contribution to the energy of interaction between different Ar atoms. Select one:a. Hydrogen bondingb. London energy, but hydrogen bonding still importantc. London energy Correctd. Dipole-dipole energy

Explanation

London forces are the result of fluctuations in the electron distribution within molecules or atoms. CHEM125 - CHAPTER 11 - BASIC HOMEWORK 1

Question 7

What is the greatest contribution to the energy of interaction between different ammonia, NH3, molecules. Select one:a. Dipole-dipole energyb. Hydrogen bonding Correctc. London energy, but hydrogen bonding still importantd. London energy

Explanation

  • Dispersion (london ) forces are present
  • Hydrogen bond is present with N (this is a greater contributor to the energy of interaction between different molecules)

Question 8

Arrange the following molecules from smallest to greatest London forces: Br2, Cl2, and I2. For Br2, Cl2, I2 write Br2, Cl2, I2 or Br2 Cl2 I2

Help: Polarizability

Answer: Correct

Explanation

Dispersion force increases with increasing molar mass because molecules or atoms of higher molar mass generally have more electrons dispersed over a greater volume.

Question 9

Arrange the following molecules from lowest to highest melting point temperature: Br2, Cl2, and I2. Answer: Correct

Explanation

Dispersion force increases with increasing molar mass because molecules oratoms of higher molar mass generally have more electrons dispersed over a greater volume.

Greater the dispersion force the stronger the intermolecular force. This means higher melting point

Question 10

In the series CH4, SiH4, GeH4, and SnH4, the boiling point increases

CHEM125 - CHAPTER 11 - BASIC HOMEWORK 4 Select one:a. because the London forces increase as the molecules get larger or the number of electrons increases. Correctb. due to hydrogen bonding.c. due to dipole-dipole forces.

Explanation

Dispersion force increases with increasing molar mass because molecules or atoms of higher molar mass generally have more electrons dispersed over a greater volume. Greater the dispersion force the stronger the intermolecular force. This means higher melting point

Question 11

Why do water, hydrogen fluoride, and ammonia have unusually high boiling points? Due to Select one:a. London forcesb. hydrogen bonding Correctc. dipole-dipole forces

Explanation

Hydrogen Bonding is the strongest among dispersion (London) , dipoles forces. CHEM125 - CHAPTER 11 - BASIC HOMEWORK 5

Question 12

All but one of the following statement is true. Using your everyday experience, check the false one. Select one:a. Evaporation takes place from the surface of water.b. A cup of soup in a bowl cools more slowly than a cup of soup on a large plate.c. Hot water evaporates from a pan faster than cool water.d. Water evaporates as a gas or vapor.e. The vapor pressure of room temperature water in a sealed glass continues to rise until the glass breaks. Correctf. The vapor pressure of room temperature water in a sealed glass reaches an equilibrium vapor pressure, that is, the evaporation rate of water equals its condensation rate from the gas phase.

Explanation

If the cup is sealed the vapor pressure can not rise easily to break the glass

Question 13

Which of the following statements are true about evaporation for a liquid?

Help: Evaporation

Select one or more:a. Only the most energetic molecules evaporate. Correctb. This means the average kinetic energy of the remaining molecules decrease. Correctc. This has no effect on the average kinetic energy of the remaining molecules.d. Consequently, the temperature of the remaining liquid drops, that is, evaporation is a cooling process. Correcte. Consequently, the temperature of the remaining liquid stays the same.

Explanation

  • Only the most energetic molecules evaporate.
  • Average kinetic energy of the remaining molecules decrease because the energetic molecules with more velocity have evaporated. Therefore the molecule in the liquid has less velocity.
  • As the water evaporates the remaining temperature of the liquid drops

Question 14

At what temperature is the equilibrium vapor pressure of water about 100 torr?

CHEM125 - CHAPTER 11 - BASIC HOMEWORK 6 Select one:a. 30oCb. 45oC Correctc. 60oCd. 80oC

Explanation

JUST LOOK AT THE GRAPH

Question 15

At what temperature is the equilibrium vapor pressure of water about 400 torr? Select one:a. 30oCb. 45oCc. 60oCd. 80oC Correct

Explanation

JUST LOOK AT THE GRAPH ABOVE

Question 16

If atmospheric pressure were 600 torr, at what temperature would water boiling? Help: Boiling Select one:a. 80oCb. 87oCc. 92oC Correctd. 100oC

Explanation

JUST LOOK AT THE GRAPH ABOVE

Question 17

Would ethanol at 80oC boil, if atmospheric pressure were 900 torr? Select one:a. Yesb. No Correctc. Maybe

Explanation

JUST LOOK AT THE GRAPH ABOVE

Question 18

A solid melts at -50oC and boils at 75oC. What happens when heat is added to the solid at -80oC?

Help: Heat transfer

Select one:a. The temperature of the solid increases. Correctb. Some solid melts as the temperature increases.c. Some solid melts, but the temperature remains the same.d. The temperature of the liquid increases.e. The liquid boils as the temperature increases.f. The liquid boils, but the temperature remains the same.

Explanation

The temperature of the solid keeps on increasing without phase changing until the it reaches the melting point at -50oC

Question 19

What happens when heat is added to the solid at -50oC? Select one:a. The temperature of the solid increases.b. Some solid melts as the temperature increases.c. Some solid melts, but the temperature remains the same. Correctd. The temperature of the liquid increases.e. The liquid boils as the temperature increases.f. The liquid boils, but the temperature remains the same.

Explanation

The solid melts at the melting point of -50oC but the temperature remains the same.

Question 20

What happens when heat is added to the liquid at 75oC? Select one:a. The temperature of the solid increases.b. Some solid melts as the temperature increases.c. Some solid melts, but the temperature remains the same.d. The temperature of the liquid increases.e. The liquid boils as the temperature increases.f. The liquid boils, but the temperature remains the same. Correct

Explanation

The liquid will boil at the boiling point of 75oC but the temperature remains the same.

Question 21

Suppose food is cooked in boiling water, using just enough heat to keep the water boiling. Would the food cook faster, if the heat were turned on high? Why? (Pick 2 answers.) Select one or more:a. Yesb. No Correctc. because The water would boil vigorously and the temperature would increase.d. because adding more energy just makes the water boil faster. The temperature would remain the same. Correct

Explanation

Once water reaches its boiling point the adding more heat will make it boil faster and evaporate faster. The temperature of the water will not change, instead water will go through as phase change from liquid to gas.

Question 22

Water exists as a solid, liquid, or gas? At 0.5 atm and -5oC, what is the phase?

CHEM125 - CHAPTER 11 - BASIC HOMEWORK 7 Select one:a. Solid Correctb. Liquidc. Gas

Explanation

CHEM125 - CHAPTER 11 - BASIC HOMEWORK 8

Question 23

At 1 torr and 0.01oC, what is the phase? Select one:a. Solidb. Liquidc. Gas Correct

Explanation

Look at the graph above CHEM125 - CHAPTER 11 - BASIC HOMEWORK 8

Question 24

At what temperature does water boil at 0.5 atm? Help: Phase change temperatures Select one:a. 100oCb. <100oC Correctc. >100oC

Explanation

Look at the graph above CHEM125 - CHAPTER 11 - BASIC HOMEWORK 8

Question 25

Check the correct statements about carbon dioxide.

CHEM125 - CHAPTER 11 - BASIC HOMEWORK 11 Select one or more:a. At -50oC and 1 atm, carbon dioxide is in the gaseous state. Correctb. At 1 atm carbon dioxide sublimes as it warms above the melting point. Correctc. At -40oC and 8 atm, carbon dioxide is in the liquid state. Correctd. As the temperature drops from -30oC to a minus -80oC at 10 atm, carbon dioxide freezes. Correct

Explanation

Look at the Graph