Answer: H 2 is thermally stable; significant energy must be supplied to create atomic hydrogen.
- A H<sub>2</sub> is thermally stable; significant energy must be supplied to create atomic hydrogen
- B H<sub>2</sub> is an inherently unstable molecule that decomposes readily at room temperature
- C Free hydrogen atoms are more thermodynamically stable than H<sub>2</sub> molecules
- D The dissociation reaction proceeds spontaneously without any energy input
Correct answer: A. H<sub>2</sub> is thermally stable; significant energy must be supplied to create atomic hydrogen
Explanation: The high H-H bond dissociation enthalpy means H<sub>2</sub> is very stable thermally; atomic H is highly reactive and rare under normal conditions.
Each water molecule's O-H bonds (covalent, solid) can hydrogen-bond (dashed) to neighbouring molecules, forming an extended network responsible for water's unusually high boiling point and density anomaly.
Concept context
The simplest and most abundant element in the universe. Study its unique position in the periodic table, isotopes (protium, deuterium, tritium), properties of water and hydrogen peroxide, and industrial uses.