Question

Deuterium resembles hydrogen in properties but :

• A. reacts vigorously than hydrogen
• B. emits \(\beta^+\) particles
• C. reacts slower than hydrogen
• D. reacts just as hydrogen

Hint:

Remember the kinetic isotope effect: bonds involving heavier isotopes are generally stronger and break more slowly. This is a fundamental concept that explains why D\(_2\)O has a higher boiling point than H\(_2\)O and why reactions involving D are slower than those with H.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for a key difference in the chemical reactivity of deuterium (D or \(^2\)H) compared to protium (H or \(^1\)H), the most common isotope of hydrogen.
Step 2: Key Formula or Approach:
Deuterium and hydrogen are isotopes, meaning they have the same number of protons and electrons, and thus very similar chemical properties. However, deuterium has a neutron, making it twice as massive as protium. This mass difference leads to differences in the rates of chemical reactions, a phenomenon known as the kinetic isotope effect.
Step 3: Detailed Explanation:
The bond dissociation enthalpy of the D-D bond (443.35 kJ/mol) is greater than that of the H-H bond (435.88 kJ/mol). Similarly, a C-D bond is stronger than a C-H bond. This is because the heavier deuterium atom has a lower zero-point vibrational energy, meaning the bond sits lower in its potential energy well and requires more energy to be broken.
Since chemical reactions often involve the breaking of bonds, reactions involving deuterium will require a higher activation energy to break the stronger bonds compared to the same reactions with protium. A higher activation energy leads to a slower reaction rate.
Therefore, deuterium reacts slower than hydrogen.
Let's analyze the other options:
(A) reacts vigorously than hydrogen - Incorrect. It reacts slower.
(B) emits \(\beta^+\) particles - Incorrect. Deuterium is a stable, non-radioactive isotope. Tritium (\(^3\)H) is the radioactive isotope that undergoes \(\beta^-\) decay.
(D) reacts just as hydrogen - Incorrect. While chemically similar, their reaction rates are different due to the isotope effect.
Step 4: Final Answer:
Deuterium resembles hydrogen in properties but reacts slower than hydrogen.