Slide 1

Rates Because diamonds aren't forever... Especially not once you heat them to 1700 o C Slide 2 Consider Two Reactions Magesnium burningIron Rusting 2Mg (s) + O 2 (g) 2MgO (s)4Fe (s) + 3O 2 (g) 2Fe 2 O 3 (s) These are basically the same reactioncombustion of a metalbut one is an unquenchable fireball of doom, and the other slowly rots your car apart. Slide 3 Why? The only real difference is rateone of these reactions is an F1 Mclaren, and the other is a horse and buggy. Slide 4 So What Makes a Reaction Fast? There are a few factors that affect the rate of a reaction: 1. Intrinsic speed 2. Surface area 3. Temperature 4. Presence of a catalyst 5. Concentration Slide 5 Intrinsic Speed Just like our horse and buggy, some things are just naturally slower than others. There are two basic reasons for this: 1. Collision orientation: Some reactions need everything to line up perfectly to react. For others, it doesn't matter as much. Slide 6 Intrinsic Speed Just like our horse and buggy, some things are just naturally slower than others. There are two basic reasons for this: 2. Activation Energy: Every reaction has an activation energysome energy that must be put in to get over the hill. The bigger the hill is, the slower the reaction will go. Slide 7 Surface Area If two things are going to react, they have to actually bump into each other There's a reason we do things in aqueous solution a lotit provides the most opportunity for one molecule or ion to whack into another. But some things won't dissolve, or would react with water. In that case...chop them up. More atoms/molecules/ions can meet up at once. Slide 8 Temperature Remember that activation energy? One way to get stuff over a hill faster is to give it a big kick: Raising the temperature gives each molecule/ion more energy to get over that hill, so it's more likely to get there quickly. Slide 9 Catalyst Alternately, just bulldoze the hill: A catalyst is something that is NOT part of the reaction equationit comes out unchangedbut lowers the activation energy. Slide 10 Concentration The simplest way to make things react faster is to have them whack into each other more often. And the simplest way to make them whack into each other more often is to just put more concentrated stuff in: Note: this only applies to solutions and gasses. Solids and liquids don't really have concentrations. Slide 11 A Question Is it linear? For example, if I double the surface area, will my rate double? Triple? Quadruple? What if I double the concentration instead? Slide 12 An Answer Is it linear? For example, if I double the surface area, will my rate double? Triple? Quadruple? What if I double the concentration instead? Take AP Chemistry and find out... (or do your own research) Slide 13 Summary Some reactions are faster than others This intrinsic speed depends on collisions and activation energy You can speed up reactions by: 1. Increasing surface area of solids 2. Heating them up 3. Adding a catalyst 4. Increasing the concentration of solutions