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WU 4/19

WU 4/19. Suggest at least two reasons why not all collisions result in a reaction. Draw an endothermic reaction pathway LABEL: reactants, products, activated complex, activation energy, enthalpy change. Learning Goals.

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WU 4/19

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  1. WU 4/19 • Suggest at least two reasons why not all collisions result in a reaction. • Draw an endothermic reaction pathway LABEL: reactants, products, activated complex, activation energy, enthalpy change

  2. Learning Goals • Explain the factors that lead to an effective collision and a chemical reaction • Describe the role of a catalyst in a chemical reaction. • Predict the effect of changes in concentration, temperature & pressure on reaction rate

  3. Content Vocabulary • Collision • Orientation • Transition state • Activated complex • Activation energy • Reaction rate

  4. Background Context • Collision Theory = Putting on Pants in the morning

  5. 18-1 Collision Theory • Effective collisions cause reactants to become products. • Not all collisions results in a reaction • Reactants must run into each other (collide) • Reactants must collide with enough energy • Reactants must collide with the proper orientation

  6. Visualizing Collision Theory • 2HI  H2 + I2 • Reactants  Products • requires a transition state characterized by: • instability • high energy • Difficult to control • EX: Child  Adult

  7. Activated complex = teenagers • A transitional structure between reactants and products. • Old bonds break and new bonds are form. • unstable, high energy • All chemical reactions have an activated complex that must form. • Activation Energy: minimum energy needed to form the activated complex. • This is the bump on reaction graphs.

  8. Depicting Reactions • Draw a reaction pathway for methane combusting. • Endothermic or exothermic? • Label the Reactants, Products, and activated complex on the graph • The ΔH is the net difference between products and reactants-- label this

  9. Activation energy • The Eact is the energy from reactants to activated complex—label this • For methane combustion, what is the source of energy to reach the activated complex?

  10. 18-1 Reaction Rate • A measure of the decrease in reactants, or the increase in products over time. • Reaction rate depends on several factors: • Nature of reactants (will they react) • Temperature- • particles move faster (think bumper cars) • Concentration & Pressure of gases • more particles (think high school dance) • Surface area • More opportunities to react

  11. 18-1 Reaction Rates • *In general, the more times you get particles to collide, the higher the rate. • Catalyst: a substance that changes the rate of a reaction, and emerges unchanged • EX: enzymes to break down food. • EX: matchmakers • Increase the RATE of reaction. • Lowers activation energy • Make it easier for activated complex to form. • Emerge UNCHANGED from the reaction

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