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Chapter_14

# Chapter_14 - Chapter 14 Rate of Reactions Studying rates of...

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CHM 1220/1225 Chapter 14 1 of 6 Chapter 14: Rate of Reactions Studying rates of reaction allows us to determine the optimum conditions for a reaction and to understand the mechanism of the reaction at a molecular level. Studying rates of reaction allows us to determine the optimum conditions for a reaction and to understand the mechanism of the reaction at a molecular level. Note: These notes omit section14.4 Change of Concentration with Time Reaction Rates 1. Definition of Rate Rate is expressed as the change in concentration of reactant or product per unit time. In order to be able to relate the rate as expressed in terms of each reactant and product, we include a “–“ for reactants (their concentration decreases) and a factor equal to the reciprocal of the coefficient. For the general reaction aA + bB –––> cC + dD 1 D [C] 1 D [D] –1 D [A] –1 D [B] Rate = c D t = d D t = a D t = b D t 2. Rate and Form of Reactant Physical State: Gases and liquids react more quickly than solids because they allow for the mixing of reactant molecules –– collisions Particle Size The smaller the solid particle, the greater the surface area, and the faster the reaction: coal chunks (require lighter fluid) vs. coal dust (explosive) 3. Rate and Concentration of Reactants and Catalyst The relationship between concentration and rate is given by the rate law: rate = k [A] X [B] Y A catalyst speeds up the reaction without being consumed; it must be included in the 4. Rate and Temperature Collision Theory assumes that, in order for a reaction to occur, • a collision is required • the collision must be in the correct orientation • the collision must have a minimum energy called the activation energy, E A Temperature : increases the number of molecules that have the minimum energy, E A Generally, as temperature increases, rate increases. A rule of thumb is that for every 10ºC increase in temperature the rate doubles.

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CHM 1220/1225 Chapter 14 2 of 6 Rate Law For the general reaction aA + bB –––> cC + dD The general rate law is rate = k [A] q [B] r [Catalyst] s
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Chapter_14 - Chapter 14 Rate of Reactions Studying rates of...

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