Problem 12 - Chemistry in 30 days

Question

Ortho and para hydrogen differ (a) In the number of protons (b) In the molecular mass (c) In the nature of spins of protons (d) In the nature of spins of electrons

Step-by-Step Solution

Answer

(c) In the nature of spins of protons.

Step 1: Understand the Concept

Ortho and para hydrogen are two forms of molecular hydrogen ( H_2 ) that differ in the relative spins of their protons. They are not different in terms of the number of protons or molecular mass. Instead, the difference lies in the orientation of nuclear spins in the hydrogen molecule.

Step 2: Examine the Spin Orientation

In ortho hydrogen, the spins of the two protons are aligned parallel to each other, meaning their spins are in the same direction. In para hydrogen, the spins of the protons are antiparallel, which means they spin in opposite directions. This difference in spin alignment influences the properties of the hydrogen molecule.

Step 3: Analyze the Options

Given the options: (a) Number of protons - both forms have the same number of protons. (b) Molecular mass - both have the same molecular mass. (c) Nature of spins of protons - ortho and para hydrogen differ in this aspect. (d) Nature of spins of electrons - they do not differ in electron spin. The difference is clearly in the nature of proton spins.

Step 4: Select the Correct Option

Based on the analysis, the correct answer is: (c) In the nature of spins of protons.

Key Concepts

Spin Orientation

Spin orientation refers to the direction in which atomic particles, such as protons, exhibit their intrinsic angular momentum or spin. In molecular hydrogen, which exists primarily as a diatomic molecule (\(H_2\)), the way these spins align significantly affects the molecule's properties.

• In ortho hydrogen, the spins of the two protons are oriented in the same direction, meaning they are parallel.
• In para hydrogen, the spins are oriented opposite to each other, or antiparallel.

The parallel and antiparallel orientations give ortho and para hydrogen their distinct characteristics. These spin configurations also define the specific quantum states of hydrogen molecules, which in turn influence how they interact with their environment.

Proton Spin

Protons possess a property called spin, which is a type of quantum angular momentum. This property is an innate feature of protons, meaning it is a basic characteristic present in all protons.

The spin of a proton can have a significant impact on the behavior of molecules when these protons are part of molecular hydrogen. Here’s what happens:

• When proton spins are parallel, as in ortho hydrogen, the molecule has a total spin value of 1. This configuration is considered a triplet state.
• When proton spins are antiparallel, as in para hydrogen, the total spin value is 0, indicating a singlet state.

The distinction between triplet and singlet states is important because it determines the energy levels, stability, and magnetic properties of the hydrogen molecules. Understanding proton spin helps us grasp why ortho and para hydrogen exhibit differences in physical properties, such as boiling points and rotational spectra.

Molecular Hydrogen

Molecular hydrogen (\(H_2\)) is the simplest form of a molecule composed of two hydrogen atoms bonded together. This molecule is fundamental in chemistry and physics due to its simplicity and the role it plays in various chemical processes.

In the context of ortho and para hydrogen:

• Molecular hydrogen has two identical protons whose spins can couple in different ways, leading to two distinct forms - ortho and para hydrogen.
• The relative abundance of ortho and para hydrogen can vary with temperature, affecting the physical properties of hydrogen gas significantly.
• This dual nature showcases the significance of quantum mechanical principles in determining the characteristics and behavior of molecules.

Studying molecular hydrogen is crucial for scientists because it helps in understanding broader principles of quantum chemistry and physics, as well as providing insights into more complex molecular systems.