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Topic: Kinetics & Equilibrium

This lesson explores the concepts of endothermic and exothermic reactions, focusing on how to determine the heat change (ΔH) associated with chemical reactions. You'll learn that an endothermic reaction absorbs energy while an exothermic reaction releases energy. The course material includes practical examples, the use of a table for heat of reactions, and energy diagrams to visualize reaction processes. Key concepts include the heat of formation and stability of compounds, enabling you to analyze various chemical reactions effectively.

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Topic: Kinetics & Equilibrium

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  1. Topic: Kinetics & Equilibrium • Aim: How do you determine if a reaction is endothermic or exothermic? • DN: Explain why an increase in temperature increases the rate of a reaction. • HW:

  2. Endothermic/Exothermic • Endothermic – energy absorbed • Hreactants = 5 kJ, Hproducts = 10 kJ • ΔH = 10 – 5 = 5 kJ • In endothermic rxns, ΔH is POSITIVE • Exothermic – energy released • Hreactants = 10 kJ, Hproducts = 5 kJ • ΔH = 5 – 10 = -5 kJ • In exothermic rxns, ΔH is NEGATIVE

  3. Heat of Reaction • Substances have potential energy or heat content • Heat of Reaction – amt of heat given off or absorbed in a rxn. • Difference between energy of reactants & energy of products • ΔH (change in heat from beginning to end)

  4. Using Table I • Heats of Reaction at 101.3 kPa and 298 K • List of reactions • Shows if rxn is endo (+) or exo (–)

  5. Reading Table I

  6. Using Table I How much heat is needed to produce 2 moles of HI? • Thought Process: • Find reaction on Table I that produces HI. • How many moles of HI did that rxn yield? (Remember # of mol. = coefficient) • How much heat was required for the reaction? • +53kJ • How much heat is needed to produce 1 mole of HI? • Answer: 53/2 = 26.5kJ

  7. Using Table I Give the ΔH Value & tell if the rxn is endo or exo 1. CH4 + 2O2 CO2 + 2H2O 2. 2CH3OH + 3O2 2CO2 + 4H2O 3. N2(g) + O2(g)  2NO(g) - How much heat is needed to produce 2 moles of NO(g)? - How much heat is needed to produce 1 mole of NO(g)?

  8. Using Table I • Determining the Heat of Formation (Hf) • Heat of Formation -the amount of heat released or absorbed when one mole of a compound is produced from its elements • (- sign indicates exothermic reaction) • What is the Hfof NO ? • +91.3 • Why? 182.6/2

  9. Using Table I • Determining if a compound is stable. Compounds with a negative Heat of Reaction are stable (more negative = more stable) Which is more stable? NH3 (g) or H2O (g) H2O (g)(-483.6) NH3 (– 91.8)

  10. Using Table I How do you draw an energy diagram for a reaction using table I? • Draw the energy diagram for the reaction producing 2 NO2

  11. Thought Question • Draw an energy diagram for an endothermic reaction and indicate with a dashed line what it would look like if a catalyst were added

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