In collision theory, what is activation energy?

• A. The minimum energy required for a collision to result in a reaction.
• B. The total energy released during a reaction.
• C. The energy of the products after the reaction.
• D. The energy input to start the experiment.

Answer: (A)

Activation energy is the minimum energy that colliding particles must have for a reaction to occur. In collision theory, a collision only leads to product formation if the particles have enough energy to reach the transition state where old bonds break and new ones form. If their energy is below this barrier, the collision will not result in a reaction, no matter how often they meet. Temperature and catalysts influence reaction rate by increasing the number of particles that have enough energy to cross that barrier or by lowering the barrier itself. The other statements refer to different concepts: the total energy released during a reaction is the reaction’s enthalpy change, not the threshold for reacting; the energy of the products is determined after the reaction occurs; and the energy input to start the experiment isn’t the concept described by activation energy.