Explain why water (H2O) boils at 100 oC whereas H2S boils at -61 oC, even though sulfur has a higher atomic weight than oxygen.

Read about hydrogen bonding. That's the secret.

c. Explain why water, (H2O) boils at 100oC at room temperature and hydrogen sulfide (H2S) at –60 oC?

The boiling point of a substance is determined by the strength of the intermolecular forces between its molecules. In the case of water (H2O) and hydrogen sulfide (H2S), both substances exhibit intermolecular forces known as hydrogen bonding.

Hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom, such as oxygen (O) or sulfur (S), and is attracted to another electronegative atom in a neighboring molecule. This creates a relatively strong dipole-dipole interaction.

In water, each molecule forms hydrogen bonds with neighboring molecules, resulting in a network of interconnected molecules. These hydrogen bonds are relatively strong and require a significant amount of energy to break down. As a result, water boils at a relatively high temperature of 100 °C.

On the other hand, hydrogen sulfide also forms hydrogen bonds but to a lesser extent compared to water. The S-H bond is weaker than the O-H bond due to sulfur's lower electronegativity. The hydrogen bonds in hydrogen sulfide are not as strong as those in water. Therefore, hydrogen sulfide boils at a much lower temperature of -61 °C.

Although sulfur has a higher atomic weight than oxygen, the strength of the intermolecular forces is determined by the nature of the chemical bonds and the electronegativity of the atoms involved, rather than the atomic weight. In this case, the electronegativity difference between oxygen and hydrogen is greater than the electronegativity difference between sulfur and hydrogen, leading to stronger hydrogen bonding in water and a higher boiling point.

To understand why water (H2O) boils at 100°C and hydrogen sulfide (H2S) boils at -61°C, we need to consider the concept of intermolecular forces and molecular structure.

First, let's discuss intermolecular forces. These forces are interactions between molecules and greatly influence a substance's boiling point. The strength of these forces varies depending on the type of molecules and the atoms they contain.

Water molecules are polar due to the electronegativity difference between oxygen and hydrogen atoms. This polarity creates hydrogen bonding, which is a strong intermolecular force. Hydrogen bonding occurs when the hydrogen atom in one molecule is attracted to the electronegative atom (oxygen) in another molecule. These hydrogen bonds are relatively strong and require more energy to break, thus raising the boiling point of water.

On the other hand, hydrogen sulfide molecules are nonpolar because the electronegativity of sulfur is similar to that of hydrogen, resulting in a negligible dipole moment. As a result, hydrogen sulfide experiences weaker intermolecular forces called London dispersion forces or Van der Waals forces. These forces arise from temporary dipoles induced by fluctuations in electron density. Since London dispersion forces are weaker compared to hydrogen bonding, less energy is required to overcome them, resulting in a lower boiling point for hydrogen sulfide.

Now, let's discuss the molecular structure. Aside from intermolecular forces, molecular size and shape also affect boiling points. In the case of water, the presence of two lone pairs of electrons on the oxygen atom creates a bent molecular shape. This arrangement allows for more efficient hydrogen bonding as the oxygen atom is partly negatively charged. In contrast, hydrogen sulfide has a linear molecular shape, with sulfur as the central atom bonded to two hydrogen atoms. This linear geometry reduces the opportunity for intermolecular attractions between hydrogen sulfide molecules.

In summary, the differences in boiling points between water and hydrogen sulfide can be attributed to the presence of strong hydrogen bonding in water due to its polar nature and bent molecular structure. Hydrogen sulfide lacks these strong intermolecular forces due to its nonpolar nature and linear molecular structure, resulting in a lower boiling point.