Class14

Class14 - Chemical Technologies and their Natural...

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Chemical Technologies and their Natural Limitations (cont.) Making decisions about technologies
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How can a technology based on a reversible reaction that has a low equilibrium yield be made economically viable? If a given amount of reactants are kept together until equilibrium is established, the equilibrium yield is called the yield/batch Industry depends on daily production yield = (yield/batch)(# batches/day) If the yield/batch is small, the daily production yield can still be made acceptable if the #batches/day can be made sufficiently large The #batches/day can be increased by speeding up the reaction so that it takes less time to make each batch
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The collision theory is very helpful in under- standing the factors that affect rates of reactions Collision Theory - for a reaction to occur, particles of the reactants must collide with sufficient energy to initiate the reaction (called the energy of activation, E a ) • Only collisions having E a produce products and hence are called fruitful collisions Rate of reaction is proportional to the product: (collision frequency) (fraction of fruitful collisions) How can the speeds of chemical reactions be increased?
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http://www.chemguide.co.uk/physical/basicrates/catalyst.html#top E a determines the fraction of fruitful collisions High E a , low fraction of fruitful collisions, means slow reaction (fruitful collisions) (Unfruitful collisions)
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http://www.wpbschoolhouse.btinternet.co.uk/page03/3_31rates.htm Concentration - increasing concentration increases collision frequency and hence increases speed Surface area - increasing surface area of a solid reacting with gases or liquids increases collision frequency and hence increases speed Speeds of reactions depend on the collision frequency and on the fraction of collisions having E a
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Temperature - increasing temperature increases both the collision frequency and the fraction of fruitful collisions http://www.wpbschoolhouse.btinternet.co.uk/page03/3_31rates.htm As temperature increases, molecules move faster and collide more frequently.
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As temperature increases, the fraction of molecules having E a also increases Increasing temperature by 10 ºC doubles to triples speeds of many reactions http://www.chemguide.co.uk/physical/basicrates/catalyst.html#top
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This note was uploaded on 10/19/2011 for the course CHEM 83 taught by Professor Bonk,j during the Fall '08 term at Duke.

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Class14 - Chemical Technologies and their Natural...

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