Controlling Chemical Reactions
This Wiki, Controlled Chemical Reactions, shows how a reaction can change within certain circumstances.
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Table of Contents
Activation Energy
Endo and exo thermic reactions
How to control chemical reactions
Controlling chemical reaction video
Enzymes

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Activation Energy
"The activation energy is the minimum amount of energy needed to start a chemical reaction."
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An example of activation energy is when you boil water. The activation energy used to boil water is heat from the stove.
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Endo- and Exo- thermic Reactions
As discussed in the previous topic, every chemical reaction needs energy to start. But whether or not a reaction needs more energy from the environment to keep going depends on if it's an exothermic or endothermic.
An exothermic reaction is a "chemical reaction where the energy content of the products is less than that of the reactants; heat is given out from the system." (matter.org.uk) this means that after the chemical reactions, the product has less energy than the reactant, releasing heat in the process.

An endothermic reaction is a "chemical reaction where the energy content of the products is more than that of the reactants; heat is taken in by the system." (matter.org.uk) this means that the amount of energy one substance increases after the chemical reaction occurs.
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How to Control Chemical Reactions
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There are a series of factors you can alter to decrease/increase chemical reactions:

  • If you increase surface area, it will speed up the reactions, and vice versa.


If you have a large piece of a solid, its surface area is very limited. When the reaction occurs between a solid and a liquid, the particles on the surface of the object comes in contact with the reactant making only a small fraction of the reactant (the solid) reacts initially with the reactant the liquid. If another experiment under the same circumstances occurs, but you take the first reactant (the solid) and slice it in to several pieces, the chemical reaction will happen much more vigorously and in less time than the reaction with the non-altered object. This happens because the surface area of the object is bombarded with the reactant, thus, making the reaction increase in speed.
  • If you increase the temperature, particles will increase in speed, causing the reaction to speed up, and vice versa.



When you increase the temperature, the particles in both the substance and the reactant’s particles increase in speed. When the two substances come in contact, the particles, which are moving much faster (due to the increase in temperature), are far more likely to come in contact with each other. Also, particles that move around more rapidly have much more energy, therefore, making the chemical reaction having much more energy. This relationship between the two can be expresses.this realationship can be expressesd through the equation K=Ae to the -Ea/RT . This could be shown in the example below:
In our video (which is below this section) we used Ascorbic Acid (Vitamin C), water, iodine, a hot plate, and an ice tub. We separated the Vitamin C and water to 3 separate containers, each exposed to different temperatures. One is settled on-top of a hot plate that is set to 75 degrees Celsius. Another is placed in an ice bath to lowers the temperature to about 10 degrees Celsius. And the last beaker is left alone in room temperature
  • If you give more of the reactant to the chemical reaction, the speed of it will increase, and vice versa.

Another way to increase or decrease a chemical reaction rate is through something called concentration. Concentration is simply just taking away or adding the volume or quantity of one reactant. If thought of correctly, it can be catagorized as common sense; if something is causing a reaction at a certain rate, and then you take some of that away, the reaction will occur slower depending on how much you take away. This also increases the rate of the reaction if you add more of the reactant.
  • By adding the reactant material it speeds up the reaction without being consumed.
The scientific name for a substance that increases the rate of a chemical reaction is a catalyst. A catalyst is what really makes the chemical reaction occur in the first place. It combines with the reactant but it never is destroyed making the chemical equilibrium of the reaction not altered at all. It can go fast and in a more selective manner, making it very ideal and important in industrial chemistry.

  • Adding a material that stops chemical reactions slows it down.

A material that slows down a chemical reaction is called an inhibitor. Inhibitors are, in a way, the exact opposite of a catalyst. Were a catalyst is something that speeds up a chemical reaction, an inhibitor is a substance that slows or stops a chemical reaction.




Enzymes


At last, we will discuss enzymes and why they are relevant to this topic: controlling chemical reactions. They are significant to this topic because enzymes are biological catalysts. They have three main functions.
1. As we said before, catalysts are substances that increase a chemical reaction rate, therefore, a enzyme is something that increases the rate of a given biological chemical reaction
2. Enzymes are normally with only one reactant (a substrate) to produce products out of chemical reactions.
3.Enzymes are regulated form a state of low activity to high activity and vice versa. Each enzyme is very important. Out of about 3,000 enzymes, if one is defective, the effect is disastrous.






Works Cited
"Role of Enzymes in Biochemical Reactions." Elmhurst College: Elmhurst, Illinois. Web. 18 May 2011. <http://public.elmhurst.edu/>.
Chang, Raymond. Chemistry. 5th ed. New York: McGraw Hill, 1994. Print.
"MATTER." M A T T E R - Materials Science & Engineering Educational Software. Web. 17 May 2011. <http://www.matter.org.uk/>.
Padilla, Michael J., Ioannis Miaoulis, and Martha Cyr. Prentice Hall Science Explorer. Vol. L. Upper Saddle River, NJ: Pearson/Prentice Hall, 2009. Print. Chemical Interactions