1 / 25

Wednesday 5/2/12

Wednesday 5/2/12 . Pick up the Reaction Rate Note Packet off the front green demo table and date it. Chemical Rxn Rates. Heat of Reaction. The amount of heat released or absorbed during a chemical reaction. Endothermic :. Reactions in which energy is absorbed as the reaction proceeds.

quinn-johns
Download Presentation

Wednesday 5/2/12

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Wednesday5/2/12 • Pick up the Reaction Rate Note Packet off the front green demo table and date it.

  2. Chemical Rxn Rates

  3. Heat of Reaction The amount of heat released or absorbed during a chemical reaction. Endothermic: Reactions in which energy is absorbed as the reaction proceeds. Exothermic: Reactions in which energy is released as the reaction proceeds.

  4. Endothermic Reactions

  5. Exothermic Reactions

  6. Chemical Kinetics The area of chemistry that concerns reaction rates. Key Idea: Molecules must collide to react. However, only a small fraction of collisions produces a reaction. Why?

  7. Collision Model Collisions must have enough energy to produce the reaction (must equal or exceed the activation energy). Orientation of reactants must allow formation of new bonds.

  8. Reaction Rate • Speed at which a chemical reaction takes place • Reaction rate depends on the collisions between reacting particles. • Determined by measuring the change in concentration of a reactant or product per unit of time

  9. Factors Affecting Reaction Rates • Temperature: Measure of average kinetic energy of the molecules in a substance • Pressure: force exerted on unit area of surface little effect on liquids & solids but a big effect on gases • Concentration: amount of molecules present in a unit volume • Catalyst: an agent that speeds up the rate of chemical rxns w/out being permanently changed or used up • Surface area: area of the surface

  10. Temperature • Molecules at higher temp. have higher KE and move fastermore collisionsfaster rxn rate • A 10°C increase in Tempdouble the rate of rxn • Temp Collisions Rxn rate

  11. Pressure • Increase of pressure increases concentration  more effective collisions of molecules & faster rxn rate • Pressure Conc Collisions Rxn Rate

  12. Concentration • Increasing concentration  increases chance of effective collisions  faster rxn rate • Conc Rxn Rate

  13. Catalysts • Provides a shorter pathway for the reactants to follow as they change into products (like a tunnel cut through a mountain) • Lowers Activation Energy • Speeds up rxn rate without being consumed in the rxn • + Catalysts Activation E Rxn Rate

  14. Ea Activation Energy (Ea) • depends on reactants • minimum energy required for a reaction to occur • low Ea = fast rxn rate

  15. Endothermic Reaction witha Catalyst

  16. Exothermic Reaction with a Catalyst

  17. Surface Area • high SA = fast rxn rate • more opportunities for collisions • Increase surface area by… • using smaller particles • dissolving in water • SA Collisions Rxn Rate

  18. Chemical Equilibrium Reversible Reactions: A chemical reaction in which the products can react to re-form the reactants Chemical Equilibrium: When the rate of the forward reaction equals the rate of the reverse reaction and the concentration of products and reactants remains unchanged 2HgO(s)  2Hg(l) + O2(g) Arrows going both directions ( ) indicates equilibrium in a chemical equation

  19. LeChatelier’s Principle When a system at equilibrium is placed under stress, the system will undergo a change in such a way as to relieve that stress.

  20. Le Chatelier Translated: When you take something away from a system at equilibrium, the system shifts in such a way as to replacewhat you’ve taken away. When you add something to a system at equilibrium, the system shifts in such a way as to use up what you’ve added.

  21. Equilibrium Shift • Consider the following reaction N2 + 3H2 2NH3 What is the effect of increasing the amount of ammonia? (which way would the equilibrium shift?)

  22. Equilibrium shift • Consider the following reaction H2O2  H2O + O2 What is the effect of decreasing the amount of H2O2 ? (which way would the equilibrium shift?)

  23. If the pressure on a system of reacting gases is increased, the rate of reaction also increases because the • A) amt. of catalyst present increases • B) conc. of reactants increases • C) temp. increases • D) # of molecules involved in the rxn increases

  24. An increase in temp. speeds the rxn rate because the • A) distance between molecules increases • B) distance between molecules decreases • C) # of collisions increases • D) # of collisions decreases As the # of collisions between reactants increases, the • A) Reaction stops • B) rate of rxn decreases • C) rate of rxn increases • D) rate of rxn remains the same

More Related