ap chem chapters 6 and 7

Ch 6 and 7 Review

Copyright © Houghton Mifflin Company. All rights reserved. CRS Question, 6–2

QUESTION

A gas absorbs 0.0 J of heat and then performs 15.2 J of work. The change in internal energy of the gas is: 1) –24.8 J. 2) 14.8 J. 3) 55.2 J. 4) –15.2 J. 5) none of these.


ANSWER

–

q

4) 15.2 J.

Section 6.1 The Nature of Energy (p. 229)

When = 0, then the internal energy equals the work.


QUESTION

For a particular process q = 20 kJ and w = 15 kJ. Which of the following statements is true? 1) Heat flows from the system to the

surroundings. 2) The system does work on the surroundings. 3) E = 35 kJ. 4) All of these are true. 5) None of these are true.


ANSWER

E

q w

3) = 35 kJ.


Internal energy = + . The heat and work both have a positive sign indicating energy flowed from the system to the surroundings.


QUESTIONWhich of the following statements is correct? 1) The internal energy of a system increases when more

work is done by the system than heat was flowing into the system.

2) The internal energy of a system decreases when work is done on the system and heat is flowing into the system.

3) The system does work on the surroundings when an ideal gas expands against a constant external pressure.

4) All statements are true. 5) All statements are false.


ANSWER

3) The system does work on the surroundings when an ideal gas expands against a constant external pressure.


The gas molecules of the atmosphere have an average distance from each other.


ANSWER (continued)

A gas from a reaction expanding into the atmosphere must force all the gas molecules nearby closer together. This is the work the gas does on the atmosphere.


QUESTIONWhich one of the following statements is false? 1) The change in internal energy, E, for a process is

equal to the amount of heat absorbed at constant volume, qv.

2) The change in enthalpy, H, for a process is equal to the amount of heat absorbed at constant pressure, qp.

3) A bomb calorimeter measures H directly. 4) If qp for a process is negative, the process is

exothermic. 5) The freezing of water is an example of an exothermic

reaction.


ANSWER

)

3) A bomb calorimeter measures H directly.

Section 6.2 Enthalpy and Calorimetry (p. 235

Enthalpy is heat at constant pressure. The pressure can change drastically inside of a bomb calorimeter.


QUESTION

For a particular process q = –17 kJ and w = 21 kJ. Which of the following statements is false? 1) Heat flows from the system to the

surroundings. 2) The system does work on the surroundings. 3) E = +4 kJ 4) The process is exothermic. 5) None of these is false.


ANSWER

E

. E

3) = +4 kJ


For a thermodynamic process we are only interested in the change of energy, E is the energy of a particular state.


QUESTION

In the lab, you mix two solutions (each originally at the same temperature) and the temperature of the resulting solution decreases. Which of the following is true? 1) The chemical reaction is releasing energy. 2) The energy released is equal to s m T. 3) The chemical reaction is absorbing energy. 4) The chemical reaction is exothermic. 5) More than one of these.


ANSWER

)

3) The chemical reaction is absorbing energy.


The temperature drops because the reactants are absorbing energy from the solution faster than the surroundings can replace it.


QUESTIONFor the reaction H2O(l) H2O(g) at 298 K, 1.0 atm, H is more positive than E by 2.5 kJ/mol. This quantity of energy can be considered to be: 1) the heat flow required to maintain a constant

temperature. 2) the work done in pushing back the atmosphere. 3) the difference in the H—O bond energy in

H2O(l) compared to H2O(g). 4) the value of H itself. 5) none of these


ANSWER

)

2) the work done in pushing back the atmosphere.


The gas molecules need to use some energy to move atmospheric gas molecules out of their way.


QUESTION

Given the equation S(s) + O2(g) SO2(g), H = –296 kJ, which of the following statement(s) is (are) true?

a. The reaction is exothermic. b. When 0.500 mole sulfur is reacted,

148 kJ of energy is released. c. When 32.0 g of sulfur are burned,

2.96 105 J of energy is released.


QUESTION (continued)

1) All are true. 2) None is true. 3) a and b are true. 4) a and c are true. 5) Only b is true.


ANSWER

)

1) All are true.


The minus sign indicates that the reaction is exothermic.


QUESTION

The heat of formation of Fe2O3(s) is –826 kJ/mol. Calculate the heat of the reaction 4Fe(s) + 3O2(g) 2Fe2O3(s) when a 55.8-g sample of iron is reacted. 1) –206 kJ 2) –413 kJ 3) –826 kJ 4) –1650 kJ 5) –3.30 10

3 kJ


ANSWER

–

)

2) 413 kJ


Don’t forget to convert grams to moles in this problem. Enthalpy is always in units of kJ/mol.


QUESTION

When 0.157 mol NH3 is reacted with excess HCl, 6.91 kJ of energy is released as heat. What is H for this reaction per mole of NH3 consumed? 1) –22.7 J 2) –1.08 kJ 3) –44.0 kJ 4) +22.7 J 5) +44.0 kJ


ANSWER

3) –44.0 kJ Section 6.2 Enthalpy and Calorimetry (p. 235) A common mistake is use the wrong sign for the enthalpy. Careful reading of the problem will indicate the sign that must be used.


ANSWER (continued)

Phrases like “heat is released”, “heat is given off” or “heat is emitted” indicate that a minus sign is used. Phrases like “heat is absorbed” or “heat is added” indicate that a plus sign is used.


QUESTION

Consider the following numbered processes:

a. A 2B b. B C + D c. E 2D

H for the process A 2C + E is


QUESTION

1) H1 + H2 + H3 2) H1 + H2 3) H1 + H2 – H3 4) H1 + 2H2 – H3 5) H1 + 2H2 + H3


ANSWER

1 – 3

)

–

4) H + 2 H2 H

Section 6.3 Hess’s Law (p. 242

The final equation is found by summing the reactions as follows: I + 2(II) III. The minus sign means the reaction is reversed.


QUESTION

Consider the following standard heats of formation:

P4O10(s) = –3110 kJ/mol H2O(l) = –286 kJ/mol H3PO4(s) = –1279 kJ/mol

Calculate the change in enthalpy for the following process:

P4O10(s) + 6H2O(l) 4H3PO4(s)


ANSWER

)

–290 kJ

Section 6.4 Standard Enthalpies of Formation(p. 246

Remember to multiply the heat of formation of each compound by its coefficient.


QUESTION

Which of the following is not being considered as an energy source for the future? 1) Ethanol 2) Methanol 3) Seed oil 4) Shale oil 5) Carbon dioxide


ANSWER

5) Carbon dioxide

Section 6.6 New Sources of Energy (p. 256)

Carbon dioxide is a very stable product of most combustion reactions. It will not react further to produce more useful heat.


QUESTION

When ignited, a uranium compound burns with a green flame. The wavelength of the light given off by this flame is greater than that of: 1) red light. 2) infrared light. 3) radio waves. 4) ultraviolet light. 5) none of these


ANSWER

4) ultraviolet light.

Section 7.1 Electromagnetic Radiation (p. 275)

As the energy of the light increases, the wavelength of the light decreases.


QUESTION

Which of the following frequencies corresponds to light with the longest wavelength? 1) 3.00 10

13 s

–1

2) 4.12 105 s

–1

3) 8.50 1020

s–1

4) 9.12 10

12 s

–1

5) 3.20 109 s

–1


ANSWER

5 –

2) 4.12 10 s1

Section 7.1 Electromagnetic Radiation (p. 275)

The smaller the frequency of light, the longer the wavelength.


QUESTION

Alpha particles 4

2He2+ beamed at thin metal foil

may: 1) pass directly through without changing direction. 2) be slightly diverted by attraction to electrons. 3) be reflected by direct contact with nuclei. 4) Both 1 and 3. 5) Statements 1, 2, and 3.


ANSWER

5) 1, 2, and 3

Section 2.5 The Modern View of Atomic Structure: An Introduction (p. 49)

These three observations were noted by Ernest Rutherford giving him clues to the nature of the atom and the existence of the nucleus.


QUESTION

Green light has a wavelength of 5.50 102 nm.

The energy of a photon of green light is: 1) 3.64 10

–38 J.

2) 2.17 105 J.

3) 3.61 10–19

J. 4) 1.09 10

–27 J.

5) 5.45 1012

J.


ANSWER

19

hc

3) 3.61 10–

J.

Section 7.2 The Nature of Matter (p. 277)

Energy of the photon = /.


QUESTION

When a hydrogen electron makes a transition from n = 3 to n = 1, which of the following statements is true?

a. Energy is emitted. b. Energy is absorbed. c. The electron loses energy. d. The electron gains energy. e. The electron cannot make this transition.



1) a, d 2) a, c 3) b, c 4) b, d 5) e


ANSWER

n

2) a, c

Section 7.4 The Bohr Model (p. 285)

Photons are emitted as an electron goes from higher to lower , and photons are absorbed as an electron goes from lower to higher n.


QUESTION

Which of the following is a reasonable criticism of the Bohr model of the atom?



1) It makes no attempt to explain why the negative electron does not eventually fall into the positive nucleus.

2) It does not adequately predict the line spectrum of hydrogen.

3) It does not adequately predict the ionization energy of the valence electron(s) for elements other than hydrogen.

4) It does not adequately predict the ionization energy of the 1st energy level electrons for one-electron species for elements other than hydrogen.

5) It shows the electrons to exist outside of the nucleus.


ANSWER

-

3) It does not adequately predict the ionization energy of the valence electron(s) for elements other than hydrogen.

Section 7.4 The Bohr Model (p. 285)

The Bohr model does not take into account electron electron repulsion, so it cannot be used for atoms or ions with more than one electron.


QUESTION

Which of the following statements about quantum theory is incorrect?


QUESTION (continued)1) The energy and position of an electron

cannot be determined simultaneously. 2) Lower energy orbitals are filled with

electrons before higher energy orbitals. 3) When filling orbitals of equal energy, two

electrons will occupy the same orbital before filling a new orbital.

4) No two electrons can have the same four quantum numbers.

5) All of these are correct.


ANSWER

–

3) When filling orbitals of equal energy, two electrons will occupy the same orbital before filling a new orbital.

Section 7.5 The Quantum Mechanical Model of the Atom (pp. 290 293)

Electrons are charged and tend to keep as far from each other as possible.


QUESTION

How many f orbitals have the value n = 3? 1) 0 2) 3 3) 5 4) 7 5) 1


ANSWER

l f

l

1) 0

Section 7.7 Orbital Shapes and Energies(p. 295)

For n = 3, can be 0, 1, or 2. An orbital has an = 3.


QUESTION

If n = 2, how many orbitals are possible? 1) 3 2) 4 3) 2 4) 8 5) 6


ANSWER

l n ml

2) 4

Section 7.6 Quantum Numbers (p. 293)

Orbitals are designated by m . For = 2, has four values.


QUESTION

The electron configuration for the barium atom is: 1) 1s

22s

22p

63s

23p

63d

104s

2

2) [Xe] 6s2

3) 1s22s

22p

63s

23p

64s

1

4) 1s22s

22p

63s

23p

64s

2

5) none of these


ANSWER

2

-

2) [Xe] 6 s

Section 7.11 The Aufbau Principle and the Periodic Table (p. 302)

[Xe] denotes a shorthand version of the electron configuration for Xe. Noble gas configurations are used to reduce writing time.


QUESTION

Which of the following combinations of quantum numbers is not allowed? n l m(l) m(s) Option 1: 1 1 0 1/2 Option 2: 3 0 0 –1/2 Option 3: 2 1 –1 1/2 Option 4: 4 3 –2 –1/2 Option 5: 4 2 0 1/2



1) Option 1 2) Option 2 3) Option 3 4) Option 4 5) Option 5


ANSWER

l n

1) Option 1

Section 7.6 Quantum Numbers (p. 293)

can have values of 0 to – 1.


QUESTION

Which of the following atoms would have the largest second ionization energy? 1) Mg 2) Cl 3) S 4) Ca 5) Na


ANSWER

5) Na

Section 7.12 Periodic Trends in Atomic Properties (p. 309)

Sodium has only one electron in its outer shell. Once this has been removed the next electron must come from the core electrons, requiring a tremendous increase in energy.


QUESTION

Nitrogen has 5 valence electrons. Consider the following electron arrangements.


QUESTION (continued) 2s 2p 1)

2) ?

3)

4)

5) Which represents the ground state for the N– ion?


ANSWER

–

5)


N ion has an extra electron that must be paired. It is isoelectronic with oxygen.


QUESTION

In which groups do all the elements have the same number of valence electrons? 1) P, S, Cl 2) Ag, Cd, Ar 3) Na, Ca, Ba 4) P, As, Se 5) none


ANSWER

5) none


Atoms in the same group have the same number of valence electrons. None of the sets of atoms have members all from the same group.


QUESTION

The first ionization energy of Mg is 735 kJ/mol. The second ionization energy is: 1) 735 kJ/mol. 2) less than 735 kJ/mol. 3) greater than 735 kJ/mol. 4) More information is needed to answer this

question. 5) none of these.


ANSWER

.

3) greater than 735 kJ/mol

Section 7.12 Periodic Trends in Atomic Properties (p. 309)

The second ionization energy is always greater than the first, because the next electron is no longer leaving a neutral atom, but one with a +1 charge.

ap chem chapters 6 and 7

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