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Revised information on Chemical Reactions By: Kelsey Berry ~Retyped everything except for experiments ENERGY AND CHEMICAL REACTIONS Chemical reactions constantly have to do with a change in energy. Energy can’t be created or destroyed. Energy can be absorbed or released in chemical reactions. Chemical reactions can be endothermic or exothermic reactions. Endothermic Reactions These are the chemical reactions in which energy is absorbed. Endothermic reaction means that energy is required for the reaction to actually occur. Usually the energy that is absorbed is often heated energy or sometimes electrical energy. Adding the electrical energy to some metal oxides can divide them into pure metal and pure oxygen. For example, Adding electrical energy to sodium chloride can cause the table salt to break into its original sodium and chlorine parts. Exothermic Reactions These are the chemical reactions when energy is released. The energy that is released is originally stored in the chemical bonds of the reactants. The heat given off causes the product to feel hot. Any reaction that involves burning is an exothermic reaction. Potential Energy It is called potential energy because it has the ability to be converted into diferent forms of energy, and to acomplish reactions in the process. The standard unit of measure for potential energy is a joule. The term potential energy was coined by the 19th century Scottish engineer and physicist William Rankine. Potential energy is energy that can be stored inside a system. It exists only when there is a force that wants to pull an object back towards its original position, only when the object somehow becomes displaced. This force is usually called a restoring force. For example, when a spring is stretched to the left, it exerts a force to the right so as to return to its original, unstretched position. According to the Principle of Conservation of Energy, energy can’t be created nor destroyed; this means that the energy can’t disappear. Instead it can be stored as potential energy. Chemical Potential energy, for example, the energy stored in fossil fuels, is due to the Coulomb Force which is rearrangement of the positions of the electrons and nuclei, in atoms and the molecules. Activation Energy In chemistry, activation energy is also called midnight energy. It happens to be a term introduced in 1889 by a Swedish scientist called Svante Arrhenius. It is defined as the energy that must be overcome in order for the chemical reaction to take place. Arrhenius’s research was a continuation of the work on the theories of reaction rate done by a Serbian physicist named Nebojsa Lekovic. Activation energy may also be defined as the least amount of energy necessary for a chemical reaction to take place. For a chemical reaction to be noticeable, there should be noticeable number of molecules with the energy equal or greater than the activation energy level. Reactants and products Reactants are the substances that enter into the reaction, and the products are the substances that are present at the end of the reaction, and are due to the chemical reaction of the reactants. An example of a chemical reaction is when you add sodium hydroxide to hydrochloric acid. The reactants are sodium hydroxide and hydrochloric acid, and the products are water and sodium chloride. NaOH (aq) + HCl (aq) = H2O (l) + NaCl (aq) Signs of a Chemical Reaction -Bubbles(like opening a soda can) -heat -cold -giving off light -change of color -formation of gas -odor change -energy produced The Law of Conservation of Mass The Law of Conservation of Mass was officially established in the year 1789 by the French Chemist, Antoine Lavoisier. The Law of Conservation of Mass states that mass is neither lost nor gained in chemical reactions, it states that it simply changes form. For that reason, if you had a certain number of atoms of a certain element on the left side of a chemical reaction equation, then you would have to have the same number of atoms of that element on the right side of the equation. This entails that mass can also be conserved during a chemical reaction. Combustion A combustion reaction can occur when oxygen combines with another compound so it will end up forming water or carbon dioxide. These reactions produce heat so they are called exothermic reactions. EXAMPLE: C10H8 + 12 O2 ---------------10 CO2 + 4 H20 Synthesis During a synthesis reaction two or more simple substances combine which forms a more complex substance. EXAMPLE: Oxygen + hydrogen combine to create water 2 H2 + O2--------------------2H2O Double Replacement During a double replacement reaction the parts of 2 compounds switch places which causes a new compound to form. EXAMPLE: AgNO3 + NaCl-------------------AgCl + NaNO3 Decomposition During a decomposition reaction a complex substance will break down and form into simpler parts. Synthesis and decomposition happen to have the same effect on substances. EXAMPLE: 2 H2O --------------------2 H2 + O2 Single Replacement During a single replacement reaction a single uncombined element replaces another in a compound. EXAMPLE: Zn + 2 HCl-------------------ZnCl2 + H2 Bibliography INFORMATION BIBLIOGRAPHY ~Carpi, Anthony. “Chemical Reactions.” Chemical Reactions. http://web.jjay.cuny.edu/~acarpi/NSC/6-react.htm (19981999). ~”Types of Chemical Reactions.” Chemical Reactions. http://educ.queensu.ca/~science/main/concept/chem/c02/c02mai n.htm. ~Eigen, Manfred; Ostwald, Wilhelm; Herschbach, Dudley R.; Hoff, Jacobus Henricus van ’t. “Chemical Reactions.” Chemical Reactions. http://www.britannica.com/EBchecked/topic/108802/chemicalreaction/49377/Basic-concepts-of-chemical-reactions. ~”Reaction (Overview).” Chemical Reactions. http://www. chem4kids.com/files/react_intro.html (1997-2007). ~Barrans, Richard. “Ask a Scientist.” Chemical Reaction Archive. http://www.newton.dep.anl.gov/askasci/chem00/chem00971.ht m (Feb 3, 2003). ~Helmenstine, Anne. “Types of Chemical Reactions.” Chemical Reactions. http://chemistry.about.com/od/chemicalreactions /a/reactiontypes.htm (2008) ~”Decomposition Reaction Lab.” Chemical Reaction Labs. http://library.thinkquest.org/18406/drlab.htm. ~”Single Replacement Lab.” Chemical Reaction Labs. http://library.thinkquest.org/18406/sdlab.htm. PICTURE BIBLIOGRAPHY (I used Google images for all pictures) ~http://popsci.typepad.com/photos/uncategorized/2007/11/27/s helterbakingsoda_2.jpg. ~http://www.webdesign.org/img_articles/7477/flame-slice_11.gif. ~http://www.freefoto.com/images/33/15/33_15_10---FireFlame-Texture_web.jpg. ~http://www.nugentec.com/images/rust.jpg. ~http://www.lowellfoods.com/files/image/products/grocery/prese rves/vinegar.jpg. ~http://www1.istockphoto.com/file_thumbview_approve/878847 /2/istockphoto_878847_steel_wool.jpg. ~http://www.lakewoodconferences.com/direct/dbimage/5014692 6/Citric_Acid.jpg. ~http://www.maths.tcd.ie/~foams/GALERY/Jelly_20foam.JPG. ~http://www.metalChina.cn/en/wire/shengjiagong/images/dinglei01.jpg. ~http://www.stainedfloor.com/CopperSulfate1.jpg.