Properties of Hydrogen — Isotopes, ortho/para
Hydrogen
4
JEE Qs
8%
Hard
60
min
Master the distinct properties and stability order of hydrogen isotopes and the conditions for interconversion and equilibrium ratios of ortho/para-hydrogen, as these are common areas for tricky questions requiring specific factual recall.
🧮 Key Formulas
✅ Key Points for JEE
- 1Hydrogen has three isotopes: Protium (¹H), Deuterium (²D or D), and Tritium (³T or T), differing in the number of neutrons and thus atomic mass, leading to distinct physical properties.
- 2Tritium is the only radioactive isotope of hydrogen (β-emitter) with a half-life of 12.33 years, while Protium and Deuterium are stable.
- 3Ortho- and para-hydrogen are nuclear spin isomers of the H₂ molecule, not chemical isomers or allotropes. Ortho-H₂ has parallel nuclear spins, and para-H₂ has anti-parallel spins.
- 4Para-hydrogen is more stable at very low temperatures and exhibits lower boiling point, specific heat, and thermal conductivity compared to ortho-hydrogen.
- 5Interconversion between ortho- and para-forms is slow unless catalyzed (e.g., by activated charcoal, atomic hydrogen, paramagnetic substances) or at high temperatures. At room temperature, the equilibrium ratio is approximately 3:1 (ortho:para); at very low temperatures, equilibrium shifts almost entirely to para-H₂.
⚠️ Common Mistakes
- ✕Confusing ortho/para-hydrogen as chemical isomers or allotropes instead of nuclear spin isomers.
- ✕Misremembering the relative stability and physical property differences (e.g., boiling point, specific heat) between ortho- and para-hydrogen.
- ✕Forgetting the conditions or catalysts required for the interconversion between ortho- and para-hydrogen.
- ✕Not knowing that Tritium is radioactive while Protium and Deuterium are stable isotopes.
📝 Practice Questions
See allQ34.Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: Loss of electron from hydrogen atom results in nucleus of ~1 . 5 × 10 – 3 pm size. Reason R: Proton H+ always exists in combined form. In the light of the above statements, choose the most appropriate answer from the options given below: (1) Both A and R are correct and R is the correct (2) A is correct but R is not correct explanation of A (3) A is not correct but R is correct (4) Both A and R are correct but R is NOT the correct explanation of A
Q41.Which of the following can reduce decomposition of H2O2 on exposure to light (1) Urea (2) Alkali (3) Glass containers (4) Dust
Q31.Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A: Hydrogen is an environment friendly fuel. Reason R: Atomic number of hydrogen is 1 and it is a very light element. In the light of the above statements, choose the correct answer from the options given below (1) A is true but R is false (2) Both A and R are true but R is NOT the correct explanation of A (3) A is false but R is true (4) Both A and R are true and R is the correct explanation of A
Q39.Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Gypsum is used for making fireproof wall boards. Reason (R): Gypsum is unstable at high temperatures. In the light of the above statements, choose the correct answer from the options given below: (1) Both (A) and (R) are correct but (R) is not the (2) (A) is correct but (R) is not correct. correct explanation of (A). (3) (A) is not correct but (R) is correct. (4) Both (A) and (R) are correct and (R) is the correct explanation of (A).
Q47.The water gas on reacting with cobalt as a catalyst forms (1) Methanal (2) Methanoic acid (3) Ethanol (4) Methanol
Q36.Given below are two reactions, involved in the commercial production of dihydrogen H2. The two reactions are carried out at temperature “T1” and “T2”, respectively T1 Cs + H2Og ⟶COg + H2g T2 COg + H2Og CatalystCO2g + H2g The temperatures T1 and T2 are correctly related as (1) T1 = T2 (2) T1 < T2 (3) T1 = 100 K, T2 = 1270 K (4) T1 > T2
NCERT Chapters
- Class 11 Chemistry Ch 10: Hydrogen