Question

Select the correct statement. (1) Para hydrogen has a lower internal energy than that of ortho hydrogen. (2) Para hydrogen is more stable at lower temperature. (3) Ortho and para hydrogen are different due to difference in their electron spins. (4) Ortho and para hydrogen are different due to difference in their nuclear spins. (a) \(1,2,3\) (b) \(1,2,4\) (c) \(2,3,4\) (d) 3,4

Short answer

(b) 1,2,4

Step-by-step solution

Understand Ortho and Para Hydrogen

Ortho and para hydrogen are two forms of molecular hydrogen that differ based on the nuclear spins of the hydrogen atoms. In ortho hydrogen, the spins of the hydrogen nuclei are aligned in the same direction, whereas in para hydrogen, the spins are antiparallel or aligned in opposite directions.

Analyze the Stability and Energy

Para hydrogen has a lower internal energy compared to ortho hydrogen, making it more stable at lower temperatures. This is because the antiparallel spin configuration of para hydrogen is energetically more favorable at lower temperatures.

Evaluate the Statements

Evaluate each statement: 1. True: Para hydrogen has a lower internal energy than ortho hydrogen. 2. True: Para hydrogen is more stable at lower temperatures. 3. False: The main difference between ortho and para hydrogen is not due to electron spins. 4. True: The difference is due to the nuclear spins.

Select the Correct Answer

Based on the analysis in the previous steps: - Statements 1, 2, and 4 are correct, whereas 3 is incorrect. - Therefore, the correct option that includes these is (b) 1,2,4.

Key concepts

Nuclear Spins

Ortho and para hydrogen are two distinct forms of molecular hydrogen. However, what sets them apart isn't as obvious as it might seem at first glance. The primary difference lies in the orientations of the nuclear spins of the two hydrogen atoms within the molecule.
In ortho hydrogen, these nuclear spins are parallel. This means they are aligned in the same direction. In contrast, in para hydrogen, the spins are antiparallel. This implies they are aligned in opposite directions.
This difference in nuclear spins is crucial. It affects the overall properties of the hydrogen molecule, influencing factors such as its internal energy and stability at various temperatures.

Para Hydrogen Stability

Why is para hydrogen more stable at lower temperatures? It's all about energy.
The antiparallel spin configuration in para hydrogen results in a lower internal energy compared to ortho hydrogen. At lower temperatures, systems generally prefer states with minimal energy for stability.
Due to its lower internal energy, para hydrogen is more favored and stable when temperatures drop. It acts as the "preferred" form because it can maintain equilibrium more efficiently than ortho hydrogen under cooler conditions.

• Lower energy means less excitation is needed for molecular transitions.
• This makes para hydrogen energetically favorable at low temperatures.

Internal Energy of Hydrogen

The internal energy of a molecule encompasses the kinetic and potential energy from the motion and interactions between its component atoms. For molecular hydrogen, this internal energy is significantly influenced by the nuclear spins.
Ortho hydrogen, with its parallel nuclear spins, has a higher internal energy. The alignment of spins results in an elevated state of energy. Conversely, in para hydrogen, the antiparallel spins create a scenario where the internal energy is minimized.
This difference directly correlates to their respective stabilities. In essence, the lower internal energy of para hydrogen makes it not just less "energetic," but more stable, especially noticeable at lower temperatures.

• Ortho hydrogen has higher potential energy due to the spin configuration.
• Para hydrogen's lower energy state contributes to its stability.