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Kinetics (Reaction Rate)

Kinetics (Reaction Rate). How Fast Does the Reaction Go. Collision Theory. In order to react molecules and atoms must touch each other. They must hit each other with enough force and with the correct orientation . The more “frequently” the particles hit, the faster the reaction will go.

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Kinetics (Reaction Rate)

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  1. Kinetics(Reaction Rate) How Fast Does the Reaction Go

  2. Collision Theory • In order to react molecules and atoms must touch each other. • They must hit each other with enough forceand with the correct orientation. • The more “frequently” the particles hit, the faster the reaction will go. • Anything that increase these effectivecollisions will make the reaction faster.

  3. Factors that Affect Rate • Temperature • Higher temperature faster particles. • More and harder collisions. • Faster Reactions. • Concentration • More concentrated closer together the molecules. • Collide more often. • Faster reaction.

  4. Factors that Affect Rate • Particle size • Molecules can only collide at the surface. • Smaller particles bigger surface area. • Smaller particles faster reaction. • Smallest possible are molecules or ions. • Dissolving speeds up reactions. • Getting two solids to react with each other is slow.

  5. Factors that Affect Rate • Catalysts- substances that speed up a reaction without being used up.(enzyme). • Speeds up reaction by giving the reaction a new path. • The new path has a lower activation energy. • More molecules have this energy. • The reaction goes faster. • Inhibitor- a substance that blocks a catalyst.

  6. Potential Energy Diagrams Represent the changes in potential energy that occur during a chemical reaction. The reaction coordinate represents the progress of the reaction.

  7. Remember in terms of energy content HIGH ENERGY =UNSTABLE LOW ENERGY = STABLE

  8. Classification of reactions Exothermic Rx: releases energy. Heat part of the products. Endothermic Rx: absorbs energy. Heat part of the reactants.

  9. Definitions Activation Energy: the minimum amount of energy needed to start up a chemical reaction. Activated Complex: a temporary intermediate product. Highest point of the diagram. Is UNSTABLE.

  10. Catalyzed Reactions Need less energy to start up the reaction. The presence of a catalyst LOWERS THE ACTIVATION ENERGY!!!

  11. Reactants Energy Products Reaction coordinate

  12. Activation Energy - Minimum energy to make the reaction happen Reactants Energy Products Reaction coordinate

  13. Activated Complex or Transition State Reactants Energy Products Reaction coordinate

  14. Reactants Energy Overall energy change (DH) Products Reaction coordinate

  15. Thermochemistry The study of the changes in heat energy that accompany chemical reactions and physical changes.

  16. What is DH? DH is theenthalpy, or “heat of reaction.” The amount of energy released or absorbed during a chemical reaction. By convention DHrxn = Hproducts - Hreactants

  17. What is an exothermic reaction? A reaction that gives off or releases heat. Since... DHrxn = Hproducts - Hreactants then DHrxn will be a negative number

  18. Reactants Energy Overall energy change (DH) Products Reaction coordinate

  19. What is an endothermic reaction? A reaction that absorbs heat. Since… DHrxn = Hproducts – Hreactants then DH will be a positive number.

  20. Products Energy Overall energy change (DH) Reactants Reaction coordinate

  21. Heats of Reaction Table I The new reference table (Table I) shows different heats of reaction for some common reactions.

  22. EXOTHERMIC RX Release heat. DH for reaction is negative The value for DH is the amount of heat released during the rx We write the heat it as PRODUCT in the chemical equation The greater the magnitude of DH the more stable the product will be!!!!

  23. ENDOTHERMIC RX Absorb heat DH for reaction is positive The value for DH is the amount of heat absorbed during the rx We write the heat it as REACTANT in the chemical equation The greater the magnitude of DH the more UNstable the product will be!!!!

  24. PAGE 140 ANSWERS RB 2012 edition 4 2 1 2 2 1 3

  25. INTERPRETING REACTION COORDINATES handout • B • A • G • G • A • F • F • F • F • B • E • I • D • J • C • H • H • A

  26. PE DIAGRAMS FOR RX • EXO • -30 • 20 • 10 • 60 • ENDO • 25 • 20 • 30 • SAME • H • E • B • G • I • F • A • C • D

  27. HEATS OF REACTION MC • 1 • 1 • 4 • 2 • 2 • 2 • 2 • 1 • 1 • 4 • 4 • 1

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