CHEM 1200 1nd Edition Lecture 6 Outline of Last Lecture I. Method of initial Ratesa. How to calculate Rate orderi. Rate 2/Rate 1 = [A]^n x [B]^m x [C]^p (for rate 2) / [A]^n x [B]^m x [C]^p (for rate 1)II. Concentration and Timea. Zeroth-Order reactionb. First-Order reactionc. Logarithm Reviewd. Confirming First Order Reactionse. Second-Order ReactionsOutline of Current Lecture I. Half-Lifea. Equations for each orderII. How can we control the rate of a chemical reaction?III. Temperature and Ratea. Collision Modelb. Activation Energyc. Arrhenius EquationCurrent LectureI. Half-Lifea. Half-life = t1/2 = the time required for the concentration of a reactant to decrease to one half its initial valuei. After one half-life, [A] = ½[A] initiallyb. First Order Reactions: after one half-life = ln 2/kThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. Independent of [A] initially!ii. Constantc. Second Order Reactionsi. 1/k[A] initially (After one half-life!)ii. Is not constant-half life gets largerd. Zeroth-Order Reactions: [A] initially/2ki. Is not constant-half-life gets smallerII. How can we control the rate of a chemical reaction?a. Concentration-molecules must collide to reactb. Physical state-molecules must mix to collidec. Temperature-molecules must collide with enough energy to reactd. The use of a catalystIII. Temperature and Ratea. Chemical reaction rates GENERALLY increase with temperature, not always thoughb. The Collision Model (i.e. collision theory)i. Reaction rates depend on collisions which in turn will likely depend on at least 3 factorsii. Collision frequency- the number of collisions per second per liter1. Higher concentration and higher temperature more frequent collisionsiii. Collision energy- the fraction of the collisions that are sufficiently forceful1. Powerful collision reaction2. Gentle collision no reactioniv. Collision orientation- the fraction of the collisions with correctly oriented molecules1. Correct alignment reactionc. Activation Energy: the minimum collision energy required for molecules to reacti. Activate complex = transition stateii. Typically, only a fraction of the molecules in a sample possess sufficient energy to reactiii. Higher the temperature, the higher this fractiond. The Arrhenius Equationi. If the reaction rate varies with temperature, so must the rate constantii. k = Ae^-E/RT1. E: activation energy2. A: frequency factor3. R: gas constant 8.314 J/mol K4. Temperature in kelvin5. Higher T larger K increased
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