2003 Benazzi - New Insights Into Parameters Controlling the Selectivity in Hydrocracking Reactions
Controlling Chemical Reactions - Merryhill School
Transcript of Controlling Chemical Reactions - Merryhill School
![Page 1: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/1.jpg)
Controlling Chemical Reactions
![Page 2: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/2.jpg)
Getting Reactions Going
• Activation Energy: the minimum amount of energy needed to start a chemical reaction
• All chemical reactions need a certain amount of activation energy to get started.
![Page 3: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/3.jpg)
Activation Energy: Example
• Consider the reaction in which hydrogen and oxygen form water. This reaction gives off a large amount of energy, but if you just mix the two gases together, they can remain unchanged for years. For the reaction to start, a tiny amount of a citation energy is needed — even just an electric spark. Once a few molecules of hydrogen and oxygen react, the rest will quickly follow because the first few reactions provide activation energy for more molecules to react.
![Page 4: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/4.jpg)
Another Look at Types of Reactions
• Exothermic Reaction (release energy): At the end of the reaction, the products have less energy than the reactants.
• Endothermic Reaction (take in energy): At the end of the reaction, the products have more energy than the reactants.
![Page 5: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/5.jpg)
Rates of Chemical Reactions
• Chemical reactions don’t all occur at the same rate.
• Some happen quickly, for example, explosions.
• Some happen much slower, for example, rusting of metal.
• If you want to make a chemical reaction happen faster, you need to get more reactant particles together more often and with more energy. To slow down a reaction, you need to do the opposite.
![Page 6: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/6.jpg)
Controlling Rates of Reactions
• Chemists can control rates of reactions by changing or using the following factors:
1. surface area
2. temperature
3. concentration
4. catalysts
5. inhibitors
![Page 7: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/7.jpg)
Surface Area
• When a chunk of solid substance reacts with a liquid or gas, only the particles on the surface of the solid come into contact with the other reactant.
• If you break the solid into smaller pieces, more particles are exposed and the reaction happens faster.
• Example: Chewing your food breaks it into smaller pieces that your body can digest more easily and quickly.
![Page 8: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/8.jpg)
Temperature• When you heat a substance, the particles move faster.
This increases the reaction rate in two ways.
1. More reactant particles come in contact more often, meaning there are more chances for a reaction.
2. Faster-moving particles have more energy causing more reactant particles to get over the activation energy “hump."
• In contrast, reducing temperature slows down reaction rates.
![Page 9: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/9.jpg)
Concentration
• Concentration is the amount of substance in a given volume.
• Increasing the concentration of reactants supplies more particles to react.
![Page 10: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/10.jpg)
Catalysts• A catalyst is a material that increases the rate of reaction
by lowering the activation energy.
• Although catalysts affect a reaction’s rate, they are not permanently changed by a reaction; therefore, they ar not reactants.
• Think of a catalyst as:
• a minister at a wedding
• a toolbox
![Page 11: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/11.jpg)
Enzymes: Biological Catalysts
• Many chemical reactions happen at temperatures that would kill most living things, but some of these reactions are necessary for life.
• Your body contains thousands of different biological catalysts called enzymes to allow these reactions to happen at a low temperature.
• Each enzyme is specific affecting only one chemical reaction.
![Page 12: Controlling Chemical Reactions - Merryhill School](https://reader031.fdocuments.in/reader031/viewer/2022012200/619d9bf938daeb2a1c53eeac/html5/thumbnails/12.jpg)
Inhibitors
• An inhibitor is a material used to decrease the rate of reaction.
• Most inhibitors work by preventing reactants from coming together.
• Usually they combine with one of the reactants either permanently or temporarily.
• Example: Adding preservatives to food