Q: Which of the following is the correct formula for calculating the enthalpy change of a reaction using average bond enthalpies?

$\Delta H_{rxn} = \Sigma (\text{bond enthalpies of bonds broken}) - \Sigma (\text{bond enthalpies of bonds formed})$

Question 1

Which of the following best describes the difference between ionic and covalent bonding?

Accepted Answer

Ionic bonding involves the transfer of electrons from a metal to a nonmetal, resulting in electrostatic attraction between ions, while covalent bonding involves the sharing of electrons between two nonmetals.

Question 2

According to the octet rule, atoms tend to gain, lose, or share electrons until they are surrounded by how many valence electrons?

Accepted Answer

$8$

Question 3

Which of the following statements about lattice energy is correct?

Accepted Answer

Lattice energy is the energy required to convert a solid ionic compound into its gaseous ions.

Question 4

Which of the following elements is most likely to form an expanded octet in a stable compound?

Accepted Answer

Phosphorus ($P$)

Question 5

A molecule of $CO_2$ has two double bonds. Which of the following is true regarding the bond length and bond strength compared to a single bond between carbon and oxygen?

Accepted Answer

The double bond is shorter and stronger than a single bond.

Question 6

Which of the following best explains why $NaCl$ has a high melting point?

Accepted Answer

It is composed of a three-dimensional lattice of oppositely charged ions held together by strong electrostatic forces.

Question 7

Which of the following molecules is an example of a molecule with an odd number of valence electrons (a free radical)?

Accepted Answer

$NO$

Question 8

Which of the following is the correct formula for calculating the dipole moment ($\mu$) of a molecule?

Accepted Answer

$\mu = Q 	imes r$

Question 9

Which of the following statements about resonance structures is correct?

Accepted Answer

Resonance structures are used when a single Lewis structure cannot accurately depict the bonding in a molecule.

Question 10

Which of the following best describes the trend in electronegativity on the periodic table?

Accepted Answer

Electronegativity increases from left to right across a period and increases from bottom to top within a group.

Question 11

A student is asked to draw the Lewis structure for $BF_3$. Which of the following is the best explanation for why boron does not have a complete octet in this molecule?

Accepted Answer

Adding more electrons to boron would place a negative formal charge on boron and a positive formal charge on fluorine, which is not favorable.

Question 12

Which of the following steps is NOT part of the Born-Haber cycle for the formation of $NaCl$ from its elements?

Accepted Answer

Direct combination of $Na$ and $Cl_2$ in the solid state without any energy changes.

Question 13

Which of the following compounds is most likely to have a polar covalent bond?

Accepted Answer

$HF$

Question 14

Which of the following is the correct formula for calculating the enthalpy change of a reaction using average bond enthalpies?

Accepted Answer

$\Delta H_{rxn} = \Sigma (	ext{bond enthalpies of bonds broken}) - \Sigma (	ext{bond enthalpies of bonds formed})$

Question 15

Which of the following best explains why transition metals often do not follow the octet rule when forming ions?

Accepted Answer

Transition metals lose their highest $n$ valence electrons first, then lose $d$ electrons as needed for the ion charge.

Question 16

Which of the following is a property of ionic compounds that distinguishes them from covalent compounds?

Accepted Answer

They are brittle, crystalline, and have high melting points.

Question 17

Which of the following best describes the dominant Lewis structure for a molecule?

Accepted Answer

The structure in which atoms have formal charges closest to zero and negative charges are on the most electronegative atoms.

Chapter 8: Basic Concepts of Chemical Bonding – Study Notes

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