Teacher Notes: This slide defines activation energy as the energy necessary to get the reaction started. Click on the link to see a simple representation of a collision with not enough energy to react <EA ,enough > or = EA energy to react, and orientation. Use the pull down menu to show a type of collision, then click on run. Once completed, use the pull down menu to show a different collision and click on run. You will do this three times.Have students read the explanation on the bottom of the animation and rewrite the concepts in their own words (paraphrase).
Diagram A vs B, The more reactant molecules, the more collisions therefore increased reaction rate.
Graph shows “hump” many reactions must overcome in order to create products.Catalysts provide an easier path for reactions to follow Enzymes are protein compounds that act as biological catalystsTeacher Notes: Definition of a catalyst. It is very important to emphasize that this foreign substance (It is not placed in the reactants or products, but placed on top of the arrow or yield sign) is not used up in the reaction. In industry some catalysts are very expensive. However, because the catalyst is not used up, it can be used over and over again. A good analogy for a catalyst is that of a matchmaker. A matchmaker makes it easier for future partners to get to know each other but after the relationship is established, the matchmaker is not involved any longer. In a way, a matchmaker reduces the tension that usually keeps people apart. That tension is like the activation energy.
Explain to students that normally hydrogen peroxide will decompose into water and oxygen over time when exposed to light. (Note the brown bottle it comes in).Prepare ahead 4 to 5 ziploc bags with hydrogen peroxide.To the first ziploc bag add a small piece of meat or potato containing the enzyme catalase. Students should note their observations.Ask students if that same enzyme or piece of meat/ potato will work in the second bag. What about the third?Enzymes ARE NOT used up.Take that piece of meat and cut it in half. Immerse a half in acid, and the other half in hotwater and leave for a min.Place each half in separate ziploc bags. Do they work? Why not?
Teacher Notes:Discuss with students chemical reactioncatalyst
Factors that affect reation rates sca144 revised music
FCAT SCA 1.4.4 Factors that Affect Rate of Reactions<br />
Chemical reactions occur when atoms rearrange.<br />Methane (CH4) and oxygen (O2) (reactants) react to form carbon dioxide (CO2) and water (H2O) (products)<br />Notice how atoms have switched partners or rearranged.<br />2<br />What is a Chemical Reaction?<br />
Collision Model <br />For reactions to occur particles must collide.<br />In order for collisions to be effective, the molecules must collide with sufficient energy called Activation Energy<br />Molecules must also collide with proper orientation <br />The rate of reaction is effected by the number of collisions of reactant molecules<br />Applet showing collision of particles with different energy (<EA and > or = EA) and orientation.<br />
Rate of Reaction <br />Rate of reaction = Quantity of product produced <br /> Time Required <br />Chemical reactions occur at different rates <br />Today we will consider some of the key factors that influence the rate of reaction <br />
Collision Model <br />Factors we will examine<br />Concentration<br />Pressure<br />Catalyst & pH<br />Temperature<br />Surface area (particle size)<br />These influence the reaction by: <br />Increasing the number of collisions OR <br />Increasing the fraction of collisions that will be successful <br />
“Back That Thang Up”<br />Roles:<br />Timer (one per class)<br />Recorder (one per class)<br />Molecule A both arms on hips<br />Molecule B one arm on hip, other arm straight on your side<br />Enzymes<br />Materials<br />Radio w/ music or CD<br />Rope<br />4 chairs or stools <br />
Concentration <br />Concentration: the amount of a substance (solute) present in a given volume of solution<br />“Packing” in more reactant molecules increases the number of collisions <br />Therefore a more concentrated solution = increased rate of reaction (makes more products)<br />A<br />B<br />
Pressure: reactant molecules are compressed in a smaller area.<br />Again reactant molecules are forced together<br />Therefore the greater the pressure = more collisions = increased reaction rate<br />Pressure<br />B<br />A<br />
What is a Catalyst ?<br />Substance that enhances the rate of chemical reaction.<br />They decrease the amount of collision energy needed to break bonds and form new ones making the fraction of successful collisions more effective, thus….<br />Catalysts lower the activation energy (collision energy)<br />
10<br />Effect of a Catalyst<br />The blue line represents a reaction without a catalyst.<br />The red line represents a reaction where a catalyst was added.<br />The activation energy is lower so the reaction will go faster.<br />
A catalyst = enzyme = protein<br /><ul><li>Can catalyst be reused? Are they consumed/ used up once a reaction occurs?
Lets look at the decomposition of hydrogen peroxide (H2O2) into water & oxygen.</li></ul>H2O2(l) H2O(l) + O2(g)<br /><ul><li>Catalysts ARE NOT being consumed itself but may be denatured by temperature or pH.
Therefore presence of catalyst @ optimal temperature and pH= increased rate of reaction </li></li></ul><li>Other Factors that influence Reaction Rates<br />Temperature &<br />Surface Area<br />
In groups of three obtain materials.<br />Select trial group:<br />Ice water: to 20 mL of water add 7 to 8 ice cubes<br />Warm water: heat about 20 mL of water in the microwave<br />Lab: Effects of Temperature & Surface Area on Reaction Rates<br />
Temperature<br />Increases energy of particles due to increase of temperature <br />Increase speed of particles and there are more successful collisions because molecules to contact one another more readily and with harder force <br />Therefore increased temperature = increased rate of reaction <br />
Surface Area<br />If particles are in the same phase (liquid/liquid or gas/gas) then it is easy for them to mix with each other<br />This gives particles maximum opportunity to collide <br />But if one of the reactants is a solid, the reaction can only take place on the SURFACE of the solid <br />The smaller the size of the particles, the greater the surface area that the reaction can take place in <br />Therefore, smaller surface area = increased rate of reaction <br />
Concentration: <br /> more reactants means faster reaction rate<br />Pressure: <br /> more collisions means faster reaction rate<br />Catalyst: <br /> lower activation energy means faster reaction rate<br />pH<br />Optimal pH means faster rate of reaction<br />Temperature: <br /> more collisions means faster reaction rate<br />Surface Area<br />Greater surface area means more collisions for a faster reaction rate<br />16<br />Factors that Affect Reaction Rate Summary<br />
Multiple Choice (MC) FCAT Question<br />Catalysts may reduce the amount of activation energy required for a chemical reaction to occur. Platinum (Pt) is a catalyst that is used in the catalytic converters in automobiles. In the graphs below, pathway x is a solid line representing the uncatalyzed reaction. The dotted line shows the catalyzed reaction. Which graph best illustrates the changes in a reaction when the catalyst reduces the amount of energy required?<br />
Short-Response (SR) FCAT Released Question<br />REPORT ON THE 2006 FCAT SCIENCE RELEASED ITEMS<br />
Student Responses<br />1<br />SCORE:<br />Catalysts are not used up in a reaction!<br />
To produce sulfuric acid (H2SO4), one industrial plant uses the “contact process,” which consists of several reactions. The initial reaction in this process uses sulfur dioxide (SO2 ) and oxygen (O2 ) in the presence of vanadium oxide (V2 O5) pellets to produce sulfur trioxide (SO3) as shown below.<br /> V2O5<br /> Pellets<br /> 2S02 (g) + O2 (g) ---------------- 2SO3 (g)<br /> Sulfur Oxygen Sulfur<br /> Dioxide trioxide<br />20<br />Short Response SC.A.1.4.4<br />Part A In the reaction between SO2 and O2, what is the role of the V2O5 pellets?<br />The vanadium oxide pellets serve as a catalyst in the reaction between SO2 and O2.<br />Part B Explain what the industrial chemist could do to increase the efficiency of the reaction.<br />To increase the reaction’s efficiency, the chemists could increase the temperature at which the reaction occurs. <br />