Question

The boiling point of \(\mathrm{C}_{6} \mathrm{H}_{6}, \mathrm{CH}_{3} \mathrm{OH}, \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) and \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NO}_{2}\) are \(80^{\circ} \mathrm{C}, 65^{\circ} \mathrm{C}, 184^{\circ} \mathrm{C}\) and \(212^{\circ} \mathrm{C}\) respectively. Which will show highest vapour pressure at room temperature: (a) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (b) \(\mathrm{CH}_{3} \mathrm{OH}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NO}_{2}\)

Short answer

\(\mathrm{CH}_{3}\mathrm{OH}\) will show the highest vapor pressure at room temperature.

Step-by-step solution

Understanding Vapor Pressure and Boiling Point

Vapor pressure is the pressure exerted by a vapor that is in equilibrium with its liquid phase at a given temperature. Generally, the higher the vapor pressure of a liquid at a given temperature, the lower the normal boiling point. Conversely, compounds with a higher boiling point at standard pressure will have a lower vapor pressure at a given temperature below their boiling point.

Comparing Boiling Points

Given the boiling points of the compounds, \(\mathrm{CH}_{3}\mathrm{OH}\) has the lowest boiling point of \(65^\circ \mathrm{C}\), and \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{NO}_{2}\) has the highest boiling point of \(212^\circ \mathrm{C}\). Therefore, the compound with the lowest boiling point will have the highest vapor pressure at room temperature.

Identifying the Compound with the Highest Vapor Pressure

Since \(\mathrm{CH}_{3}\mathrm{OH}\) has the lowest boiling point among the given compounds, it will have the highest vapor pressure at room temperature. This makes \(\mathrm{CH}_{3}\mathrm{OH}\) the correct answer.

Key concepts

Physical Chemistry

Physical Chemistry is the branch of chemistry focused on the study of the physical properties of molecules, the forces that act upon them, and the energy changes associated with chemical reactions. It connects the macroscopic world that we can observe with the microscopic world of atoms and molecules, using principles from physics.

One of the key areas of physical chemistry is the study of phase equilibria and transitions, which includes the relationship between vapor pressure and boiling point. This is crucial because it gives us insight into how substances change state from liquid to gas and vice versa. Understanding these concepts is not only vital for academic purposes but also has real-world applications in designing distillation processes, pharmaceuticals, and even everyday cooking methods.

In the context of our exercise, recognizing how vapor pressure relates to boiling point allows us to predict which compound will have the highest vapor pressure at room temperature, which in this case is methanol (\(\mathrm{CH}_3\mathrm{OH}\)), due to its lowest boiling point.

JEE Exam Preparation

The Joint Entrance Examination (JEE) is a highly competitive exam in India for admission into engineering programs. The JEE tests students on their understanding of various subjects, including physics, chemistry, and mathematics.

To excel in physical chemistry for JEE preparation, students must understand fundamental concepts like vapor pressure and boiling point, as they are frequently tested. Developing adept problem-solving skills through practice and understanding the underlying principles is important. For instance, being able to relate boiling point and vapor pressure quickly could prove useful in a pressure situation like the JEE, where efficiency and accuracy are key.

Therefore, practicing exercises similar to the one provided here and thoroughly understanding the step-by-step solution is vital for JEE aspirants. Knowing the correlation between intermolecular forces, vapor pressure, and boiling point is a topic that often appears in the physical chemistry section of the exam.

Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion that act between neighboring particles: atoms, molecules, or ions. They are weaker than the intramolecular forces that hold compounds together but are fundamental in determining the physical properties of substances, including boiling points and vapor pressures.

For instance, hydrogen bonding, a type of strong dipole-dipole interaction, is present in compounds such as methanol (\(\mathrm{CH}_3\mathrm{OH}\)). The intermolecular forces present in a compound determine how readily particles escape into the vapor phase, which directly correlates with vapor pressure. Substances with strong intermolecular forces require more energy to escape from the liquid to the vapor phase, exhibiting lower vapor pressures at a given temperature.

Understanding the types of intermolecular forces and how they influence boiling point and vapor pressure can significantly help in predicting the behavior of chemical substances. By analyzing the given compounds' boiling points and recognizing that lower boiling points correlate with weaker intermolecular forces and hence higher vapor pressures, students can effectively determine that methanol will exhibit the highest vapor pressure at room temperature.