Question

The reactions with low activation energy are:

• A. Slow
• B. Fast
• C. Non-spontaneous
• D. Always spontaneous

Hint:

Low activation energy \(\Rightarrow\) high rate constant \( k \) \(\Rightarrow\) faster reaction. Spontaneity depends on \( \Delta G \), not \( E_a \).

Answer 1

The Correct Option is B

Step 1: Understanding Activation Energy
Activation energy (\( E_a \)) is the minimum energy required for reactants to transform into products by crossing the energy barrier. The lower the \( E_a \), the more readily the molecules can overcome this barrier. Step 2: Link to Reaction Rate
According to the Arrhenius equation: \[ k = A e^{-E_a / RT} \] where:
\( k \): rate constant,
\( E_a \): activation energy,
\( R \): gas constant,
\( T \): temperature. From this relation, a lower \( E_a \) leads to a larger \( k \), resulting in a faster reaction rate. Step 3: Clarifying Misconceptions
- Spontaneity is determined by Gibbs free energy change (\( \Delta G \)), not activation energy.
- A fast reaction doesn’t mean it’s spontaneous, and a spontaneous reaction might still be slow if \( E_a \) is high. Conclusion: Reactions with low activation energy tend to be fast, regardless of spontaneity.