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UB CHE 102 - First/Second Orde Reactions, Half Life, and Temp./ Rate

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Chem 102 1st Edition Lecture 3 Outline of Last Lecture- Chapter 14 part 2I. Colligative Properties cntd.A. Osmotic PressureII. Chemical KineticsA. Thermodynamics vs. KineticsB. Reaction RatesC. Rate LawOutline of Current Lecture I. First-Order ReactionsII. Second-Order ReactionIII. Half-LifeIV. Temperature and RateA. Collision ModelB. Activation Energy/ Arrhenius EquationCurrent LectureI. First-Order Reactions- rate depends upon concentration of 1 reactant raised to the firstpower. The rate doubles as the concentration of a reactant doubles.-A graph of ln[A]t vs. t is a straight lineII. Second-Order Reactions- Rate depends on 1 reactant concentration raised to the 2nd power.These 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.-A graph of 1/[A]t vs. t is a straight line but ln[A]t vs. t is not.III. Half-Life- The time taken for concentration of a reactant to drop to half of it original value. ***Pharmacy students, this is used to tell how long prescription drugs will be in your system*** -First order does not depend on concentration but second order does.IV. Temperature and Rate-Rate and temperature both increase as the other increases, reactions speed up as temperature increase. For example, if you take food out of the fridge it will spoil faster. The temperature is increasing and so is the rate of spoiling. –Temperature also has to do with light. The higher the temperature, the faster the reaction, and the brighter the light. A. The Collision Model- Rate of reactions are affected by concentration and temperature. -Scientists developed a model that explained why rates of reactions increased as concentration and temperature did too. -The collision model showed that the more collisions that happened the faster the rate. -The more molecules that were present, thegreater the probability of collision, therefore, the faster the rate. -However, there was a problem. Not every single collision that took place lead to a product. Actually, only a small fraction of collisions did. This meant that in order for a reaction to occur, the collision had to be in the perfect orientation and energy. But, the higher the temperature, then the greater the energy available to the molecules, and the faster the rate.B. Activation Energy/ Arrhenius Equation-Activation energy-The minimum amount of energy required to initiate a chemical reaction…activate it. -Arrhenius discovered that something like activation energy must exist because in order for the reaction to occur, bonds had to be broken, and energy is required to break bonds. His equation:Arrhenius Equation:-k being the rate constant, Ea is the activation energy, R is the gas constant, T is temperature, and Ae is the frequency factor. Ae is a measure of the probability of a favorable


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