Answer: Reactions with lighter isotopes (H) are faster than with heavier ones (D) because zero-point energy is higher for C-H.
- A Reactions with lighter isotopes (H) are faster than with heavier ones (D) because zero-point energy is higher for C-H
- B All isotopes of a given element react at exactly the identical measured rate under most conditions encountered as frequently observed in practice
- C Heavier isotopes such as deuterium consistently react faster than ordinary protium in many documented cases according to conventional understanding
- D Changing the reaction temperature has little measurable effect on isotope-substituted reactions in routine practice
Correct answer: A. Reactions with lighter isotopes (H) are faster than with heavier ones (D) because zero-point energy is higher for C-H
Explanation: Primary KIE: C-H bonds break faster than C-D bonds because C-H has higher zero-point energy, lower activation barrier.
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.