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Chem 2AB

Chem 2AB. Rates of Reaction. Reaction Rates. 2H 2(g) + O 2(g)  2H 2 O + Energy. H 2(g) + O 2(g) can be mixed without reacting. Enthalpy. - H. Reaction Progress. Knowing the energy profile of a reaction does not tell us anything about the speed of the reaction.

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Chem 2AB

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  1. Chem 2AB • Rates of Reaction

  2. Reaction Rates 2H2(g) + O2(g) 2H2O + Energy H2(g)+ O2(g) can be mixed without reacting Enthalpy -H Reaction Progress Knowing the energy profile of a reaction does not tell us anything about the speed of the reaction

  3. Reactions occur at different rates Fast: Oxidation: Paper burning Slow: Oxidation: Nails rusting Paper turning yellow

  4. Reactions occur at different rates The speed of a reaction is called the rate of the reaction. rusting baking explosion slow fast very fast

  5. Collision theory • For a reaction to occur reactants must collide.

  6. Successful collisions A reaction won’t happen if there is: Insufficient energy to break bonds. N2 O2 N2 O2 Molecules are not alignedcorrectly.

  7. Effective collisions For reactants to make products: • 1. Molecules must collide with sufficient energy • They have to collide in the correct • orientation

  8. Activation Energy • The activation energyEa • is the minimum energy needed for a reaction to take place

  9. Energy diagrams A temporary state where bonds are reforming. Show the DE during a reaction. Activated Complex Activation energyEa Energy -H

  10. Factors Influencing Rates • Reaction rates can be affected by the nature of reactants • Precipitation reactions are fast as they have a lower Ea • Reaction that require bond breaking are slower as the Ea is higher.

  11. Changing the rate of reactions Anything that increases the number of successful collisions between reactant particles will speed up a reaction. • Factors are: • temperature • increased concentration of dissolved reactants, and increased pressure of gaseous reactants • increased surface area of solid reactants • use of a catalyst.

  12. Reaction Rates When temperature increases • More particles have higher average kinetic energy so • more particles have greater than or equal to the activation energy • leading to more successful collisions • therefore an increase in rate

  13. Reaction Rates Concentration of solutions or gases : • If • The reactant concentration increases • there is an increase in the no of collisions • and so an increase in the % of successful collisions • Therefore an increase in reaction rate.

  14. 8 blocks: 34 surfaces 8 blocks: 24 surfaces Reaction Rates State of subdivision of solids: • More Reactants: More surface area  More collisions

  15. Uncatalysed reaction Catalysed reaction Reaction Rates Catalyst: provides an alternative pathway with a lower activation energy The catalyst Is not used up during the reaction.

  16. Uncatalysed reaction Catalysed reaction Lower activation energy Reaction Rates Catalyst: • Adding a Catalyst: Lower Eact More collisions Enzymesare biological catalysts.

  17. Catalytic Converter

  18. Catalytic Converter

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