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Reaction Energy and Kinetics. Chapter 17. Temperature = Thermal Energy. 90 0 C. 40 0 C. Energy Changes in Chemical Reactions. Heat is the transfer of thermal energy between two bodies that are at different temperatures. Temperature is a measure of the thermal energy. - PowerPoint PPT Presentation

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  • Reaction Energy and Kinetics

    Chapter 17

  • Heat is the transfer of thermal energy between two bodies that are at different temperatures.Energy Changes in Chemical ReactionsTemperature is a measure of the thermal energy.greater thermal energy

  • The specific heat (s) of a substance is the amount of heat (q) required to raise the temperature of one gram of the substance by one degree Celsius.The heat capacity (C) of a substance is the amount of heat (q) required to raise the temperature of a given quantity (m) of the substance by one degree Celsius.C = msHeat (q) absorbed or released:q = msDtq = CDtDt = tfinal - tinitial

  • s of Fe = 0.444 J/g 0CDt = tfinal tinitial = 50C 940C = -890Cq = msDt= 869 g x 0.444 J/g 0C x 890C= -34,000 J

  • Constant-Volume CalorimetryNo heat enters or leaves!

  • Constant-Pressure CalorimetryNo heat enters or leaves!6.5

  • Chemistry in Action:Fuel Values of Foods and Other Substances1 cal = 4.184 J1 Cal = 1000 cal = 4184 J

  • 14.5Reaction MechanismsThe overall progress of a chemical reaction can be represented at the molecular level by a series of simple elementary steps or elementary reactions.The sequence of elementary steps that leads to product formation is the reaction mechanism.N2O2 is detected during the reaction!

  • 14.5Intermediates are species that appear in a reaction mechanism but not in the overall balanced equation. An intermediate is always formed in an early elementary step and consumed in a later elementary step.The molecularity of a reaction is the number of molecules reacting in an elementary step.Unimolecular reaction elementary step with 1 moleculeBimolecular reaction elementary step with 2 moleculesTermolecular reaction elementary step with 3 molecules

  • Exothermic ReactionEndothermic ReactionThe activation energy (Ea) is the minimum amount of energy required to initiate a chemical reaction.14.4

  • A catalyst is a substance that increases the rate of a chemical reaction without itself being consumed.ratecatalyzed > rateuncatalyzed14.6

  • The Rate LawThe rate law expresses the relationship of the rate of a reaction to the rate constant and the concentrations of the reactants raised to some powers.Rate = k [A]x[B]yreaction is xth order in Areaction is yth order in Breaction is (x +y)th order overall

  • What is the equation for the overall reaction?What is the intermediate?NO3What can you say about the relative rates of steps 1 and 2?rate = k[NO2]2 is the rate law for step 1 so step 1 must be slower than step 2