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Difficulty: EasyRate of Reaction and Collision Theory

When the temperature of a reacting system is increased, the rate of reaction increases. According to collision theory, which of the following best explains this increase?

  1. The fraction of colliding particles with kinetic energy equal to or greater than the activation energy increases significantly.Answer
  2. B
    The activation energy of the chemical reaction is lowered by the increase in thermal energy.
  3. C
    The enthalpy change (ΔH\Delta H) of the reaction increases, making the reaction more exothermic.
  4. D
    The total number of reactant molecules increases, raising the molar concentration of the system.

Answer

The rate of reaction increases because higher temperature increases the fraction of colliding particles possessing kinetic energy equal to or exceeding the activation energy.
According to collision theory, increasing temperature increases the average kinetic energy of the molecules. This results in a much larger fraction of colliding molecules having energy equal to or greater than the activation energy (EaE_a), thereby dramatically increasing the rate of successful collisions.

Step-by-Step Solution

1
Recall the two main requirements for an effective collision according to collision theory.
Effective collisions require particles to collide with correct orientation and with energy greater than or equal to the activation energy (EaE_a).
Collision theory states that not all collisions produce products.
2
Analyze the impact of increasing temperature on molecular kinetic energy.
Higher temperature increases the average kinetic energy of reactant particles, broadening the Maxwell-Boltzmann energy distribution curve.
Temperature is a measure of the average kinetic energy of particles.
3
Determine why this leads to a faster reaction rate.
A significantly larger fraction of collisions now possess energy E≥EaE \ge E_a, leading to a higher frequency of successful (effective) collisions.
This exponential increase in effective collisions is the primary reason for the increased rate of reaction.

Key Concept

Effect of Temperature on Kinetic Energy and Activation Energy in Collision Theory
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Topics

Rate of Reaction and Collision Theory