Effect of Temperature on Rate

Effect of Temperature on Rate

Reactant molecules must reach a ____________ energy state to begin the bond-breaking and bond-making processes that make up a chemical reaction. The minimum amount of energy needed for a reaction to occur is called the ____________, Ea. As the activation energy increases, the rate constant ____________ and the reaction proceeds more ____________. The rate constant varies non-linearly with ____________. For similar reactions under comparable conditions, the one with the smallest activation energy will occur most ____________.

 

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A high-energy state in the rearrangement of bonds, called the ____________ state or activated complex, occurs during chemical reactions. These species are very short lived and usually undetectable by most analytical instruments. Because of the strain placed on the bonds that are breaking, the transition state is ____________ in energy than both the reactants and products regardless of the overall energy change, ΔH, of the reaction.

 

The ____________ equation shows the relationship between the rate constant, activation energy, frequency of collisions, orientation, and temperature. The frequency factor found in the equation indicates the number of ____________ that occur with the correct orientation per unit time at a given temperature. ____________ concentrations usually result in more collisions, explaining why reaction rate often ____________ with increasing reactant concentration. These collisions must also occur with sufficient ____________ to penetrate the valence shell and rearrange the electrons to make new bonds. As the temperature increases, so does the average ____________ energy and the number of particles with energy sufficient to overcome the ____________ energy. If the activation energy is much larger than the average kinetic energy of the molecules, the reaction will occur ____________ since only a few fast-moving molecules will have enough energy to react. If the activation energy is much smaller than the average kinetic energy of the molecules, a large fraction of molecules will be adequately energetic and the reaction will proceed ____________.

It is easiest to determine the frequency factor through experiment in which the rate constant is measured at different temperatures. The form of the Arrhenius equation used for the determination of A is

 

 

And the two-point form is used to determine the rate constant at a different temperature or to determine activation energy depending on the data you already have.

 

Practice Problems

 

  1. Rate constants for the reaction 2 NO2(g) → 2 NO(g) + O2(g) are 0.77 M−1·s−1at 603 K and 4.7 M−1·s−1at 656 K.
  2. Calculate the value of the activation energy in kJ/mol.
  3. Calculate the rate constant at 626 K.