Question 1

Which of the following statements best explains why inorganic ionic compounds generally have higher melting points than organic ionic liquids?

Accepted Answer

Inorganic ionic compounds have higher ionic charges and smaller ion sizes, resulting in stronger electrostatic forces according to $$F = \frac{kQ_1Q_2}{r}.$$

Question 2

Given the reaction: $$\mathrm{C_2H_4} + \mathrm{Cl_2$} \rightarrow \mathrm{C_2H_4Cl_2}$$, and the following bond enthalpies: $$\mathrm{C=C}$$: 602 kJ/mol, $$\mathrm{Cl-Cl}$$: 240 kJ/mol, $$\mathrm{C-C}$$: 346 kJ/mol, $$\mathrm{C-Cl}$$: 654 kJ/mol. What is the estimated enthalpy change ($$\Delta H) $$for the reaction?

Accepted Answer

$$\Delta H = -158 kJ$$

Question 3

Which of the following best describes lattice energy?

Accepted Answer

The energy released when one mole of an ionic solid is formed from its gaseous ions.

Question 4

According to Coulomb's law, which combination of ions will produce the strongest ionic bond?

Accepted Answer

Ions with the largest charges and the smallest distance between them.

Question 5

Which of the following is a correct application of the second law of thermodynamics?

Accepted Answer

A process is spontaneous if it increases the entropy of the universe.

Question 6

Why is it difficult to measure lattice energy directly for ionic compounds?

Accepted Answer

Because the process involves gas-phase ions, which are hard to isolate experimentally.

Question 7

Which of the following best describes a spontaneous process?

Accepted Answer

A process that occurs by itself and continues until equilibrium is reached.

Question 8

If the bond enthalpy for breaking a $$\mathrm{C-H}$$ bond is 413 kJ/mol and for forming a $$\mathrm{C-Cl}$$ bond is 328 kJ/mol, what is the enthalpy change when one $$\mathrm{C-H}$$ bond is replaced by a $$\mathrm{C-Cl}$$ bond?

Accepted Answer

$$\Delta H = 85 kJ ($$absorbed)

Question 9

Which of the following statements about bond enthalpy is correct?

Accepted Answer

Bond enthalpy is the average energy required to break one mole of a specific bond in the gas phase.

Question 10

Which of the following would increase the lattice energy of an ionic compound?

Accepted Answer

Decreasing the distance between ions.

Question 11

A student claims that the first law of thermodynamics can predict the direction of a spontaneous process. Is this correct? Why or why not?

Accepted Answer

No, because the first law only deals with energy conservation, not spontaneity.

Question 12

Which of the following best explains why the melting point of N-butylpyridinium nitrate (an organic ionic liquid) is much lower than that of NaCl?

Accepted Answer

The ions in N-butylpyridinium nitrate are larger and have more delocalized charges, resulting in weaker electrostatic attractions.

Question 13

Which of the following is the correct expression for the force between two ions according to Coulomb's law?

Accepted Answer

$$F = \frac{kQ_1Q_2}{r}$$

Question 14

Which of the following processes is nonspontaneous?

Accepted Answer

The rolling of a rock uphill without external force.

Question 15

Which of the following steps is NOT part of the Born-Haber cycle for calculating lattice energy?

Accepted Answer

Direct measurement of lattice energy in the laboratory.

Question 16

If a reaction has $$\Delta H \u003c 0$$, what does this indicate about the reaction?

Accepted Answer

The reaction releases heat to the surroundings.

Question 17

Which of the following is true about entropy ($$S) in $$the context of the second law of thermodynamics?

Accepted Answer

The total entropy of the universe increases in a spontaneous process.

Question 18

Which of the following best describes why lattice enthalpy is considered a state function?

Accepted Answer

Because it can be calculated from the sum of enthalpy changes for steps that lead to the same final state.

Question 19

Which of the following is the correct method to estimate the enthalpy change ($$\Delta H) $$for a reaction using bond enthalpies?

Accepted Answer

$$\Delta H = 	ext{sum of bond enthalpies for bonds broken} - 	ext{sum of bond enthalpies for bonds formed}$$

Ionic Bonding, Lattice Energy, Bond Enthalpy, and Thermodynamics

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