Q.How do you convert para hydrogen into ortho hydrogen?

Para hydrogen is converted back into ortho hydrogen by heating it to a high temperature (or by exposing it to a catalyst such as charcoal, or to electric discharge/atomic hydrogen), since ordinary hydrogen at high temperature is an equilibrium mixture rich in the ortho form.

Hydrogen exists as two spin isomers depending on the relative spin orientation of the two nuclei in the H2 molecule:

• Ortho-hydrogen: both nuclear spins are parallel (same direction).
• Para-hydrogen: the two nuclear spins are antiparallel (opposite direction).

At very low temperatures (close to absolute zero), hydrogen exists almost entirely as para-hydrogen (the lower-energy form). As temperature increases, the equilibrium mixture shifts towards a higher proportion of ortho-hydrogen; at room temperature and above ("normal" hydrogen), the equilibrium composition is about 75% ortho and 25% para, and above roughly 800 K it approaches this 3:1 ortho:para ratio essentially completely.

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Heating pure para-hydrogen to a high temperature (around 1000 K) converts a fraction of it into ortho-hydrogen, because the ortho form is entropically favoured at higher temperature; at equilibrium at high T, hydrogen exists as the "normal" roughly 3:1 ortho:para mixture.

Hydrogen exists as two nuclear-spin isomers depending on the relative orientation of the two proton (nuclear) spins in the H2 molecule:

• Para-hydrogen: the two nuclear spins are opposed (antiparallel/paired) -- this is the lower-energy, lower-entropy form.
• Ortho-hydrogen: the two nuclear spins are aligned in the same direction (parallel) -- this is the higher-energy, higher-entropy form (it has 3 possible spin states versus para's 1, giving it greater degeneracy/entropy).

At absolute zero, hydrogen exists as essentially 100% para-hydrogen (the lowest-energy state). As temperature is raised, thermal energy allows population of the higher-energy ortho states, and the equilibrium mixture shifts towards the ortho form. At room temperature and above, the equilibrium ("normal") mixture is about 75% ortho-hydrogen and 25% para-hydrogen (statistical spin-state ratio of 3:1).

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Heating pure para hydrogen to a high temperature (or exposing it to a catalyst/electric discharge) converts some of it into ortho hydrogen, until the equilibrium 3:1 ortho:para ratio (ordinary/normal hydrogen) is reached.

Hydrogen exists in two nuclear-spin isomeric forms, differing in whether the spins of the two nuclei (protons) in the H2 molecule are aligned in the same direction (ortho hydrogen, parallel spins) or in opposite directions (para hydrogen, antiparallel spins). Ortho hydrogen is slightly higher in energy than para hydrogen, and at very low temperatures (near absolute zero) essentially all hydrogen exists as para hydrogen, since it is the lower-energy, more stable form under those conditions.

As the temperature is raised, some of the para hydrogen molecules absorb enough energy to flip one nuclear spin and convert into ortho hydrogen. This conversion is normally very slow because it requires a change of nuclear spin, which is a spin-forbidden, and hence sluggish, process. To make the conversion happen at a useful rate, the sample is either:

1. Heated strongly (to around 800 degree C, i.e., about 1073 K), which supplies enough thermal energy for spin-flipping to occur, or

2. Passed through an electric discharge, or

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