Review of Kinetics

  1. Rate of a chemical reaction is the change in concentration of reactants and products over time.
  2. For every mole of propane that reacts 5 moles of oxygen react, therefore, the rate of loss of oxygen is 5 times the rate of loss of propane.
  3. A) changes in concentration of any species, and appearance of blue Cu(NO3) solution

B) changes in concentration of any species, and pressure or volume changes

C) changes in concentration of any species, and pressure or volume changes

D) changes in concentration of any species, and change in pH

  1. Temperature, surface area (for heterogeneous reactions), concentration, nature of reactants, addition of a catalyst.
  2. A) rapid because reactants are simple ions in aqueous solution

B)slower than A) because the ions are more complex, but still relatively fast because they are ions in solution

C)slowest because they are uncharged atoms that must rely on collision frequency and effective collisions to overcome the activation energy barrier and form product

  1. An activated complex is a short lived, high-energy intermediate particle formed at the peak of the activation energy barrier.


  2. An increase in temperature increases both the collision frequency and the fraction of effective collisions. At higher temperatures, more particles collide and collisions occur with more force. Increasing the temperature by 10°C effectively doubles the number of particles with sufficient activation energy to form the activated complex, and, hence, product.
  3. The spark provides the activation necessary to get the reaction going. Once the reaction proceeds, there is enough energy in the system for it to be self-sustaining.
  4. The activation energy barrier is high enough that an initial input of energy is required to get the combustion reaction going. Once the reaction proceeds, there is enough energy in the system for it to be self-sustaining.
  5. Collision theory explains how molecules must collide with the correct collision geometry and the requisite activation energy in order to react and how modifying specific factors affect the speed at which reactions occur.
  6. Simple ions in aqueous solution react readily because they have a medium within which they can move and, due to their opposing charges, they will attract. Complex, uncharged molecules must rely on collisions with the correct orientation and with sufficient energy to overcome the activation energy barrier and form product. Meeting all of these conditions makes product formation much less probable, and therefore, much slower.
  7. The highest point on an energy diagram of a reaction represents the energy of the activated complex at the peak of the activation energy barrier.
  8. The activation energy of a reaction is the minimum energy required for molecules to come together and form the activated complex, the first step in the successful formation of product.
  9. A homogeneous catalyst is a catalyst that is present in the same phase as the reactant particles. For example, solid sodium chlorate decomposes in the presence of solid manganese dioxide catalyst. A heterogeneous catalyst is a substance present in a different phase than the reactant species. The decomposition of hydrogen peroxide proceeds at a rapid rate upon the addition of solid manganese dioxide.
  10. The rate of a reaction is fastest at the beginning of the reaction because the concentration of all reactant particles is greatest. More reactant particles mean a greater number of collisions, resulting in the formation of more product particles.
  11. The answer is C.
  12. The order of a chemical reaction is the relationship between the initial concentration of a reactant, raised to the appropriate exponent, to the reaction rate.
  13. The order of a reaction must be determined experimentally by systematically varying the initial concentrations of each reactant species and observing the quantitative effect on the reaction rate.
  14. Rate is a measure of the change in concentration of reactant or product species over time. The rate constant is an unchanging variable in the rate law which is expressed in the form

Rate = k [A]xfor the reaction A  B

  1. A) No, concentration is a separate variable

B)No, pressure is related to volume, and volume is related to moles, which is part of concentration

C)Yes, when temperature is increased, the rate is affected by more than only changes in concentration, therefore, the value of k must change

  1. A) 1st order with respect to concentrations of A and B, and 2nd order overall

B)2nd order with respect to the concentration of B, and 2nd order overall

C)1st order with respect to the concentration of A, 2nd order with respect to the concentration of B, and 3rd order overall

  1. An elementary reaction is one step in the series of steps leading to the overall reaction. The rate law of an elementary reaction can be determined stoichiometrically.
  2. An elementary reaction is one step in the series of steps leading to the overall reaction. The series of elementary steps is called the reaction mechanism.
  1. A) exothermicB) endothermicC) endothermicD) exothermic
  1. Enthalpy of reaction is negative when oil burns. Heat is released and the reaction is highly exothermic.
  1. A) positiveB) negativeC) negativeD) negative
  1. A) Reaction is first order with respect to concentrations of NH4+ and NO2-, and second order overall.

B) Rate = k [NH4+]1[NO2-]1

C)k = 2.7 x 10-4 L/mol•s

D)1.7 x 10-4 (mol/L•s)

E)change in conductivity, pressure, volume, and, of course, changes in concentration