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Kinetics Studies the speed of chemical reactions
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Reaction Rate can be measured in: time (sec, min, hr) mass/time (lb/sec, kg/hr) moles/time.
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BATCH
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For a Batch Process the Reaction Rate is calculated by time (sec, min) to complete the reaction
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CONTINUOUS
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Reaction Rate for Continuous Process moles/hr, kg/hr, kg/s, etc. –How much product is being formed per time (manufacturing) –How quickly a reactant is being used per time (pollution control) kJ/hr, J/s, etc. –How much energy is being released/absorbed per time (energy production)
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How is the Rate of a Chemical Rxn Changed?
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Kinetic Theory The kinetic theory of gases & fluids describes a gas as many small particles (atoms or molecules) which are in constant, random motion. The rapidly moving particles constantly collide w/ each other & w/ the walls of the container.
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Collision theory states that reactions occur when reactants hit in the proper orientation with enough force to cause a reaction.
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Petri Dish Demonstration or Video of Kinetic and Collision Theory
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If you can increase the number of collisions or force of the collisions you will change reaction rates.
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Factors that effect the rate because they effect on number of collisions
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Concentration Concentration is defined as the amount of material (mass, mol) per volume. Increasing concentration increases chances of collision because more reactants in same volume.
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Oxidation of Fe Wool Demo
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Surface Area of the Reactants The more exposed the reactants are to each other the greater the chance of a collision. BETTER
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In what state of matter does a reaction proceed most quickly? Gases are the best BETTER
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Water Cooler Gone Wrong
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Mixing If you mix a reaction solution you increase the chances of reactants coming in contact by increasing motion of reactants and exposing reactants.
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Heat increases speed of atoms and molecules making it more likely they will come in contact.
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Factors that effect the force of collision (or the force necessary)
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Heat also increases the force of collisions
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Catalysts lower the amount of force / energy needed.
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Catalysts help convert reactants into products by making a different activated complex
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Catalysts change the reaction by changing the pathway
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Sometimes a single step rxn is broken down into several steps making rxn easier
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List of Factors that Can Effect the Reaction Rate Concentration Energy - Heat, Light Catalysts Surface Area (inc. State of Matter) Mixing
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END
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Heat and Energy –There is always a need for activation energy. This energy is used to break bonds and overcome repulsion forces of valence electrons. Activation Energy
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Determining Rate Laws Page 574 sample problem, 575 sample problem, 582 #12 and 16
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Rate Law A + B C R c = k[A] x [B] y
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Energy Absorbed or Released by a Reaction and the Speed of the Reaction are Different. Fast and Lots of Energy are Explosions
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Notice that just like the instantaneous speed for a car is not the same as its average speed, the instantaneous rxn rate of a chemical rxn is not equal to its average rxn rate
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INSTANTANEOUS Reaction aA + bB cC + dD [A] a [B] b rate = Constant for specific reaction at a specific temperature, reaction vessel, etc. k k
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Solids are not involved in reaction rates because their concentration does not change. Their surface area though would be present in the constant.
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Notice that the length of reaction and reaction rate are inversely proportional. As one goes up the other goes down.
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Many reactions consist of several steps one of which will be RATE LIMITING and so this step will determine the speed for the entire rxn
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2O 3 + hv 3O 2 Important reaction
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Dueling Ozone Rxns in the Atmosphere O 2 (g) + hv 2 O (g) 2 O (g) + O 2 (g) O 3 (g) CFCl 3 (g) CFCl 2 (g) + Cl Cl (g) + O 3 (g) ClO + O 2 (g) BOTTOM RXN IS VERY SLOW
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We will move on to solutions, molarity and equilbrium next
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Dissolving Knowing what factors influence the rate of a chemical reaction, what factors would influence the rate at which a solute would dissolve into the solvent?
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2 SO 2 (g) + 2 NO 2 (g) 2 SO 3 (g) + 2 NO (g) 2 NO (g) + O 2 (g) 2 NO 2 (g) 2 SO 2 (g) + 2 O 2 (g) 2 SO 3 (g) The lead chamber process which used to be a major step in a process to make Sulfuric Acid uses nitrogen dioxide as a catalyst
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