Question

Hydrogen peroxide \(\left(\mathrm{H}_{2} \mathrm{O}_{2}\right)\) is a syrupy liquid with a relatively low vapor pressure and a normal boiling point of \(152.2^{\circ} \mathrm{C} . \mathrm{Ra}-\) tionalize the differences of these physical properties from those of water.

Short answer

The differences in the physical properties of hydrogen peroxide (H₂O₂) and water (H₂O) can be rationalized by the differences in their molecular structures and intermolecular forces. Hydrogen peroxide has a nonplanar structure with more hydrogen bonding sites and stronger hydrogen bonds than water. These stronger intermolecular forces lead to hydrogen peroxide's higher boiling point of \(152.2^{\circ} \mathrm{C}\) compared to water's boiling point of \(100^{\circ} \mathrm{C}\). Additionally, the stronger forces between hydrogen peroxide molecules result in a lower vapor pressure compared to water.

Step-by-step solution

Examine Molecular Structures

First, let's examine the molecular structure of both hydrogen peroxide and water. Water has a simple structure with one oxygen atom bonded to two hydrogen atoms at a 104.5-degree angle forming a bent geometry. It is a polar molecule. Hydrogen peroxide is more complex, with a shape resembling an open book - two oxygen atoms are joined by a single bond, and each oxygen atom is bonded to a hydrogen atom. This molecule also has a nonplanar structure, which makes it a polar molecule.

Intermolecular Forces Explication

Now, let's discuss the intermolecular forces (IMF) that explain the differences in physical properties of hydrogen peroxide and water. The key intermolecular force in both molecules is hydrogen bonding. Hydrogen bonds are generally stronger than other intermolecular forces like dipole-dipole interactions and London dispersion forces. In water, the polar nature of the H₂O molecule combined with the relatively high electronegativity of oxygen leads to strong hydrogen bonds between water molecules. In hydrogen peroxide, stronger hydrogen bonds are also observed due to the presence of two oxygen atoms in the molecule. The nonplanar structure of hydrogen peroxide enables the presence of more hydrogen bonding sites than a water molecule.

Connection Between IMF and Physical Properties

Given that hydrogen peroxide has more hydrogen bonding sites when compared to water, it means that there are stronger forces between hydrogen peroxide molecules. These stronger intermolecular forces result in a higher boiling point for hydrogen peroxide. Regarding vapor pressure, the stronger intermolecular forces in hydrogen peroxide also play a role. Since the molecules are strongly attracted to each other, fewer molecules become a gas at a given temperature, which leads to a lower vapor pressure for hydrogen peroxide.

Comparison of The Boiling Points

Lastly, let's compare their boiling points explicitly. Water has a boiling point of \(100^{\circ} \mathrm{C}\), while hydrogen peroxide has a higher boiling point of \(152.2^{\circ} \mathrm{C}\). This can be explained by the stronger hydrogen bonds in hydrogen peroxide. In conclusion, the differences in the physical properties of hydrogen peroxide and water can be rationalized by the differences in their molecular structures and intermolecular forces. Hydrogen peroxide has more hydrogen bonding sites and stronger hydrogen bonds than water, leading to its higher boiling point and lower vapor pressure compared to water.

Key concepts

Hydrogen Bonds

Hydrogen bonds are a special type of intermolecular force that significantly influences the properties of molecules. They occur when a hydrogen atom is bonded to a highly electronegative atom, like oxygen, and interacts with another electronegative atom nearby. This interaction is key to understanding the physical properties of many molecules, including water and hydrogen peroxide.

• In water, hydrogen bonding arises due to the bond between hydrogen and the electronegative oxygen atom. These bonds are strong and numerous, contributing to water's high boiling point and surface tension.
• For hydrogen peroxide, hydrogen bonds also form between the hydrogen and the two oxygen atoms. The structure allows for even more potential bonding sites than in water.

Due to these bonds, molecules like hydrogen peroxide exhibit stronger attraction forces, influencing their boiling points and vapor pressures.

Molecular Structure

The molecular structure of a substance is crucial in determining how it behaves physically and chemically. Water and hydrogen peroxide, though similar in elements, differ in how these atoms are arranged.

• Water (\( ext{H}_2 ext{O}\)) has a bent shape due to the two hydrogen atoms bonded to a single oxygen atom. The 104.5-degree angle between the bonds gives water its polar nature.
• Hydrogen peroxide (\( ext{H}_2 ext{O}_2\)) has a more complex structure often likened to an open book. Two oxygen atoms are joined by a single bond, with each further bonding to a hydrogen atom. This shape is nonplanar and contributes to the molecule's polarity.

The structural differences provide hydrogen peroxide with more hydrogen bonding sites compared to water, affecting their physical properties like boiling points.

Boiling Point

The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure. It's a key characteristic determined by the strength of intermolecular forces in the liquid.

• Water boils at \(100^{\circ} ext{C}\) under normal atmospheric pressure due to its strong hydrogen bonds.
• Hydrogen peroxide has a boiling point of \(152.2^{\circ} ext{C}\) because it forms more and stronger hydrogen bonds compared to water.

Stronger intermolecular forces, like those in hydrogen peroxide, require more energy (in the form of heat) to break. Hence, oxygen-peroxide bonds result in a higher boiling point than in water.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature. The strength of a substance's intermolecular forces plays a crucial role in determining this property.

• Water, with strong hydrogen bonds, exhibits moderate vapor pressure as its molecules are strongly attracted to one another.
• Hydrogen peroxide has even stronger intermolecular forces due to more hydrogen bonding sites, resulting in a comparatively lower vapor pressure.

This lower vapor pressure implies that at any given temperature, fewer hydrogen peroxide molecules escape into the gas phase compared to water. Thus, strong intermolecular forces correlate with low vapor pressures, as seen in hydrogen peroxide.