The critical temperature of water is higher than that of O2 because H2O molecule has:

A. Fewer electrons than O2

B. Two covalent bonds

C. V-shape

D. Dipole moment

The critical temperature of a substance is the temperature above which it cannot exist as a liquid, regardless of the pressure applied. In the case of water (H2O) and oxygen (O2), the critical temperature of water is indeed higher than that of oxygen. This difference can be attributed to the unique properties of the water molecule, particularly its dipole moment. Therefore, the correct answer to your question is D. Dipole moment.

Understanding the Dipole Moment

A dipole moment arises in a molecule when there is a difference in electronegativity between the atoms involved in a bond. In water, the oxygen atom is more electronegative than the hydrogen atoms. This creates a partial negative charge near the oxygen and a partial positive charge near the hydrogens, resulting in a polar molecule. The V-shape of the water molecule further enhances this polarity, as the angle between the hydrogen-oxygen-hydrogen bonds is about 104.5 degrees.

Why Does This Matter?

The presence of a dipole moment in water leads to strong intermolecular forces known as hydrogen bonds. These bonds occur when the positive end of one water molecule is attracted to the negative end of another. This interaction significantly increases the energy required to separate the molecules, thus raising the critical temperature of water compared to oxygen, which is a nonpolar molecule and does not exhibit such strong intermolecular attractions.

Comparative Analysis of H2O and O2

• Electrons: While it’s true that H2O has fewer electrons than O2 (10 vs. 16), this factor alone does not account for the differences in critical temperature.
• Covalent Bonds: Water has two covalent bonds, but O2 also has a strong double bond between its two oxygen atoms. Thus, the number of covalent bonds does not explain the higher critical temperature of water.
• Molecular Shape: The V-shape of water contributes to its polarity, but it is the dipole moment that is the key factor in determining the strength of intermolecular forces.

Real-World Implications

The high critical temperature of water is crucial for life on Earth. It allows water to remain in a liquid state over a wide range of temperatures, facilitating various biological processes. In contrast, oxygen, with its lower critical temperature, exists as a gas under normal conditions, which is essential for respiration in living organisms.

In summary, the dipole moment of water is the primary reason for its higher critical temperature compared to oxygen. This property leads to stronger hydrogen bonding, which significantly influences the physical state of water at various temperatures and pressures.