Activation energy is the:

Question

BlackTom AI · Accepted Answer

Activation energy is the minimum energy barrier that reactant molecules must overcome for a reaction to proceed and form products.

1. Relevant knowledge points and concepts
- Activation energy (Ea): the energy threshold between reactants and the transition state on a reaction coordinate diagram.
- Transition state: a high-energy, unstable arrangement of atoms at the peak of the energy barrier.
- Arrhenius equation: k = A·e^(-Ea/RT), showing reaction rate depends exponentially on Ea.
- Enzymes/catalysts: lower Ea, increase rate, but do not change overall energy released or absorbed (ΔH).

2. Step-by-step reasoning
- Reactions do not proceed spontaneously at molecular scale unless colliding molecules have sufficient kinetic energy to reach the transition state.
- The activation energy quantifies that required kinetic/thermal energy per collision.
- Lowering Ea (e.g., by a catalyst) increases the fraction of collisions with energy ≥ Ea, raising the reaction rate, consistent with the Arrhenius factor e^(-Ea/RT).

3. Intermediate steps / illustrative relation
- If Ea is large, e^(-Ea/RT) is small → small rate constant k.
- Example: doubling Ea (at fixed T) reduces e^(-Ea/RT) dramatically, slowing reaction; decreasing Ea increases k.
- No numerical computation is required here, but the Arrhenius relation demonstrates the role of Ea in starting reactions.

4. Why the correct answer is correct
- "Energy required to start a reaction" directly describes Ea: the minimum energy needed to reach the transition state and initiate product formation.

5. Why the other options are incorrect
- "Energy released during reactions": refers to enthalpy change (ΔH), not activation energy.
- "Energy stored in ATP": specific chemical energy in ATP molecules, unrelated to the general concept of Ea.
- "Energy of enzymes": enzymes are proteins that affect Ea (lower it); they are not the energy itself.

6. Conclusion
The correct choice is "Energy required to start a reaction," which matches the given authoritative answer.

Activation energy is the:单项选择题

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No activation energy is required for an exergonic reaction

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The energy diagram for the elementary reaction, X(g) + Y(g) ⇌ Z(g) + R(g) is shown below. What would happen if the kinetic energy of the reactants was not enough to provide the needed activation energy?

The rate constant of a reaction is measured at different temperatures. A plot of the natural log of the rate constant as a function of the inverse of the temperature (in kelvins) yields a straight line with a slope of –8.55 103 K–1. What is the activation energy (Ea) for the reaction?

The rate constant of a reaction is measured at different temperatures. A plot of the natural log of the rate constant as a function of the inverse of the temperature (in kelvins) yields a straight line with a slope of –8.55 × 103 K–1. What is the activation energy (Ea) for the reaction?

A reaction is followed and found to have a rate constant of 3.36 × 104 M-1s-1 at 344 K and a rate constant of 7.69 M-1s-1 at 219 K. Determine the activation energy for this reaction.

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