Published on

a supplemental resource for students

Published in: Education, Technology
1 Like
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide


  1. 1. Kinetics: the Rate of Chemical Reaction Lecture 21
  2. 2. It is now time to learn <ul><li>How fast the reaction is proceeding at a given moment; </li></ul><ul><li>What the reactant and product concentrations will be when the reaction is complete; </li></ul><ul><li>Whether the reaction will proceed by itself and release energy or it will require energy to proceed. </li></ul>
  3. 3. Chemical equilibrium in a chemical process is the state in which the chemical activities or concentrations of the reactants and products have no net change over time.
  4. 4. Chemical thermodynamics studies the effects of changes in temperature, pressure, and volume on chemical systems at the macroscopic scale by analyzing the collective motion of their particles.
  5. 5. Chemical kinetics is the study of rates of chemical processes, the changes in concentrations of reactants (or products) as a function of time.
  6. 6. Key factor of reaction rate: concentration <ul><li>Molecules must collide to react. </li></ul><ul><li>Reaction rate is proportional to the concentration of reactants. </li></ul><ul><li>Rate ~ collision frequency ~ concentration. </li></ul>
  7. 7. Key factor of reaction rate: physical state <ul><li>Molecules must mix to collide. </li></ul><ul><li>The more finely divided a solid or liquid reactant, the greater its surface area per unit volume, the more contact it makes with the other reactant, and the faster the reaction occurs. </li></ul>
  8. 8. Key factor of reaction rate: temperature <ul><li>Molecules must collide with enough energy to react. </li></ul><ul><li>At a higher temperature, more collisions occur in a given time. </li></ul><ul><li>Raising the temperature increases the reaction rate by increasing the number and, especially, the energy of the collisions. </li></ul><ul><li>Rate ~ collision energy ~ temperature. </li></ul>
  9. 9. Key factor of reaction rate: catalysis <ul><li>A catalyst effects a lower activation energy, which in turn makes the rate constant larger and the rate higher. </li></ul><ul><li>In more detail - on Wednesday. </li></ul>
  10. 11. Rate is a change in some variable per unit of time.
  11. 12. Rate of motion = change in position x 2 — x 1 ∆x ------------------------- = -------------- = -------- change in time t 2 — t 1 ∆t
  12. 13. Rate of growth = change in height l 2 — l 1 ∆ l ------------------------- = -------------- = -------- change in time t 2 — t 1 ∆t
  13. 14. Reactant concentrations decrease while product concentrations increase. Consider A  B
  14. 15. The change in concentration of reactant A in A  B is always negative.
  15. 16. The change in concentration of product B in A  B is always positive.
  16. 17. Rate of concentration = change in concentration of A = — --------------------------------------- = change in time concentration A 2 — concentration A 1 = — ----------------------------------------------- = t 2 — t 1 ∆ (conc A) = — -------------- ∆ t .
  17. 18. Use square brackets to express concentration in moles per liter: ∆ [A] ∆ [B] Rate = — ------------ or ------------- ∆ t ∆ t
  18. 19. The rate of the reaction itself varies with time as the reaction proceeds. The rate decreases during the course of the reaction.
  19. 22. Reaction rates: different approaches <ul><li>Average rate; </li></ul><ul><li>Instantaneous rate; </li></ul><ul><li>Initial rate. </li></ul>
  20. 23. A sample problem on expressing rate in terms of changes in concentration with time.
  21. 24. THE END