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Chapter 9: Problem 38

When liquid benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) boils, does the gas consist of molecules, ions, or separate atoms? Explain.

Short Answer

Expert verified
When liquid benzene boils, the gas consists of benzene molecules.

Step by step solution

01

Understand the Chemical Nature of Benzene

Benzene \(\text{C}_6\text{H}_6\) is a molecular compound made up of six carbon atoms and six hydrogen atoms in a specific ring structure.
02

Determine the State Change

When benzene boils, it undergoes a physical change from a liquid to a gas.
03

Analyze the Physical Change

Boiling is a phase change process where the intermolecular forces between the benzene molecules are overcome, allowing them to move freely as gas molecules.
04

Identify the Nature of the Gas

Despite the state change, the chemical composition of benzene remains the same. In the gaseous state, benzene still consists of \(\text{C}_6\text{H}_6\) molecules.
05

Conclusion

The gas does not split into ions or separate atoms because the boiling process only breaks intermolecular forces, not the intramolecular bonds within the molecules.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Physical Change
When liquid benzene (C₆H₆) boils, it undergoes a physical change. This means that its physical state changes from liquid to gas, but its chemical composition remains unchanged. Physical changes alter only the state or appearance of a substance, without changing its molecular structure.
For example:
  • Melting ice to water involves a physical change.
  • Freezing water to ice is another physical change.
During boiling, the energy (heat) added to benzene makes the molecules move faster, breaking the intermolecular forces holding them together in the liquid state. The molecules then spread out and move freely as a gas.
Intermolecular Forces
Intermolecular forces are the forces of attraction or repulsion between molecules. In the case of benzene boiling, these forces are broken to transform from liquid to gas.
Types of intermolecular forces include:
  • Van der Waals forces: Weak forces found in all molecules.
  • Dipole-dipole interactions: Stronger forces found in polar molecules.
  • Hydrogen bonds: Very strong forces found when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine.
Benzene molecules experience Van der Waals forces due to its non-polar nature. Boiling benzene requires overcoming these Van der Waals forces, allowing the molecules to escape into the gas phase. The higher the intermolecular forces, the more energy (in the form of heat) is needed to boil the liquid.
Molecular Composition
The molecular composition of a substance refers to the types and numbers of atoms in a molecule and how they are bonded together. Benzene (C₆H₆) has a ring structure with six carbon atoms and six hydrogen atoms. Even when it boils and turns into a gas, the molecular composition of benzene does not change.
Key points about molecular composition:
  • It remains constant during physical changes like boiling.
  • It ensures benzene remains as C₆H₆ in the gas state.
  • It does not split into ions or separate atoms during boiling.
The process of boiling impacts only the intermolecular forces, not the intramolecular bonds that hold the atoms within a molecule together. Hence, even in gas form, benzene retains its molecular composition of C₆H₆.

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Most popular questions from this chapter

Which member of each pair is less metallic? (a) I or O (b) Be or Ba (c) Se or Ge

Born-Haber cycles were used to obtain the first reliable values for electron affinity by considering the EA value as the unknown and using a theoretically calculated value for the lattice energy. Use a Born-Haber cycle for \(\mathrm{KF}\) and the following values to calculate a value for the electron affinity of fluorine: \(\begin{array}{ll}\mathrm{K}(s) \longrightarrow \mathrm{K}(g) & \Delta H^{\circ}=90 \mathrm{~kJ} \\ \mathrm{~K}(g) \longrightarrow \mathrm{K}^{+}(g)+\mathrm{e}^{-} & \Delta H^{\circ}=419 \mathrm{~kJ} \\\ \mathrm{~F}_{2}(g) \longrightarrow 2 \mathrm{~F}(g) & \Delta H^{\circ}=159 \mathrm{~kJ} \\ \mathrm{~K}(s)+\frac{1}{2} \mathrm{~F}_{2}(g) \longrightarrow \mathrm{KF}(s) & \Delta H^{\circ}=-569 \mathrm{~kJ} \\\ \mathrm{~K}^{+}(g)+\mathrm{F}^{-}(g) \longrightarrow \mathrm{KF}(s) & \Delta H^{\circ}=-821 \mathrm{~kJ}\end{array}\)

Rank the members of each set of compounds in order of increasing ionic character of their bonds. Use polar arrows to indicate the bond polarity of each: (a) \(\mathrm{HBr}, \mathrm{HCl}, \mathrm{HI}\) (b) \(\mathrm{H}_{2} \mathrm{O}, \mathrm{CH}_{4}, \mathrm{HF}\) (c) \(\mathrm{SCl}_{2}, \mathrm{PCl}_{3}, \mathrm{SiCl}_{4}\)

Using the periodic table only, arrange the elements in each set in order of increasing EN: (a) I, Br, \(\mathrm{N}\) (b) \(\mathrm{Ca}, \mathrm{H}, \mathrm{F}\)

Rank the members of each set of compounds in order of \(\mathrm{de}\) creasing ionic character of their bonds. Use partial charges to indicate the bond polarity of each: (a) \(\mathrm{PCl}_{3}, \mathrm{PBr}_{3}, \mathrm{PF}_{3}\) (b) \(\mathrm{BF}_{3}, \mathrm{NF}_{3}, \mathrm{CF}_{4}\) (c) \(\mathrm{SeF}_{4}, \mathrm{TeF}_{4}, \mathrm{BrF}_{3}\)
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