Problem 7 - A Complete Resource Book in Chemistry for JEE Main

Question

Ortho and para hydrogen differ (a) in the molecular weight (b) in the number of protons (c) in the nature of spin of electrons (d) in the nature of spin of protons

Step-by-Step Solution

Answer

Ortho and para hydrogen differ in the nature of the spin of protons (d).

Step 1: Understand the Problem

We need to identify the key difference between ortho and para hydrogen. The options suggest differences related to molecular weight, number of protons, spin of electrons, and spin of protons.

Step 2: Recall Hydrogen Properties

Both ortho and para hydrogen are molecular forms of hydrogen (H_2). Since they both consist of Hydrogen atoms, they have the same molecular weight and the same number of protons (Option a and b are incorrect).

Step 3: Focus on Spin

The key difference between ortho and para hydrogen lies in the spin of their protons. In ortho-hydrogen, the spins of the two protons are parallel, whereas in para-hydrogen, the spins are antiparallel.

Step 4: Analyze Electron Spin

There is no actual difference in the spin of electrons for ortho and para hydrogen. Thus, the nature of electron spin does not contribute to the distinction between ortho and para hydrogen (Option c is incorrect).

Step 5: Conclusion

The correct answer is related to the spin of protons, as ortho and para hydrogen differ in this aspect.

Key Concepts

Ortho hydrogen

Ortho hydrogen is a form of molecular hydrogen where the spins of the two protons are aligned in a parallel manner. This means that both protons' spins are going in the same direction. It's like two tops spinning in the same direction. The parallel orientation of the spins isn't just a simple detail; it actually influences the properties of the hydrogen molecules.

• When hydrogen is in the ortho state, it has slightly higher energy compared to para hydrogen.
• This higher energy level affects how ortho hydrogen behaves at different temperatures.

In terms of abundance, ortho hydrogen is more common at room temperature, making up about 75% of hydrogen molecules. It is also important to note that the abundance can vary with changes in temperature.

Para hydrogen

Para hydrogen differs from ortho hydrogen due to the opposite or antiparallel spins of its protons. This means the spins are oriented in opposite directions, like one top spinning clockwise and the other counterclockwise.

• This antiparallel spin configuration provides para hydrogen with a lower energy state.
• Consequently, para hydrogen tends to be more stable and is more abundant at very low temperatures.

At room temperature, para hydrogen accounts for the remaining 25% of hydrogen molecules. Its lower energy state is key in various scientific and industrial processes, like enhancing the efficiency of cryogenic applications.

Proton spin

Proton spin is a fundamental property of protons, similar to the idea of tiny magnets. Every proton has a spin, which can be thought of as a rotation around its axis. In molecular hydrogen, how these proton spins are oriented in relation to each other gives rise to different forms of hydrogen.

• When both proton spins are aligned in the same direction, the result is ortho hydrogen.
• When they are opposed to each other, it forms para hydrogen.

The spin of protons in a hydrogen molecule adds a level of complexity and is essential for understanding its physical behavior. It directly affects the molecule's energy state and stability.

Molecular hydrogen

Molecular hydrogen, represented as \( H_2 \), is a molecule consisting of two hydrogen atoms bonded together. It's one of the simplest and most abundant molecules in the universe. The bond between the two hydrogen atoms is covalent, meaning they share electrons, leading to a very stable form of hydrogen.

• Hydrogen molecules can take the form of either ortho or para hydrogen, depending on the proton spin orientation.
• It plays a crucial role in numerous chemical processes and serves as a fundamental building block in chemistry.

In scientific research and industry, distinguishing between ortho and para hydrogen is significant due to their differing energy states and applications, especially in low-temperature physics and quantum computations.