By Ollie Auerbach

A chemical Reaction  A process in which atoms of the same or different elements rearrange themselves to form a new substance. While they do so, they either absorb heat or give it off

Chemical Reaction Basics  What is happening during a chemical reaction?  Reactants react to form products.  Reactants- the materials that exist before the chemical reaction  Products- substances that are created by the chemical reaction  Atoms are only rearranged.  No new atoms are created.  What part of atoms are affected by chemical reactions?  A chemical reaction involves the motion of electrons in the forming and breaking of chemical bonds. 

Signs of a chemical reaction  Bubbling  Change in temperature  Light is emitted  Change in color  Energy is produced  A gas is produced  A precipitate forms ( chemical reaction that forms a solid powder from two liquid substances)  

Law of Conservation Mass  In a chemical reaction, matter is neither gained or lost  Or more simply put, the mass of substances produced (products) by a chemical reaction is always equal to the mass of the reacting substances (reactants).  

Energy in Chemical Reactions  Chemical reactions always involve a change in energy. Energy is neither created or destroyed. Energy is absorbed or released in chemical reactions. Chemical reactions can be described as endothermic or exothermic reactions.

Exothermic/ Endothermic Reactions ExothermicEndothermic  Energy is released  The energy released was originally stored in the chemical bonds of the reactants.  Any reaction that involves combustion (burning) is an exothermic chemical reaction.  Often the heat given off causes the product(s) to feel hot  Ex. – Dissolving ammonia chloride into water,  Ex. - 2H 2 +O 2 changes to 2H 2 O  type.htm type.htm  Energy is absorbed  Energy is required for reaction to happen  Energy absorbed is usually electrical energy or heat energy  Ex. –Photosynthesis,  sunlight + 6CO 2 (g) + H 2 O(l) = C 6 H 12 O 6 (aq) + 6O 2 (g)

Activation Energy  Energy that must be overcome for a chemical reaction to occur  The energy often needed to initiate a certain process   

Chemical Potential Energy  Energy that is stored and can be transformed into other forms of energy  Sound  Heat  Electricity  Light

Combustion  The act or process of burning  O 2 will always be a reactant in a combustion reaction  When something burns it is almost always a combustion reaction  Combustion reactions are almost always exothermic (Give off heat)  An example- the combustion of hydrogen and oxygen, which is a commonly used reaction in rocket engines:  2H 2 + O 2 → 2H 2 O(g) + heat. The result is water vapor.   

Decomposition  The state of being reduced into original elements. (breaking down, disintegration)  Opposite of combination reactions  Compound decomposes (splits up)  Basic formula- AB ---> A + B  An example- Water broken down into hydrogen and oxygen  2H 2 O → 2H 2 + O 2 

Synthesis  The combining of separate elements or substances to form a whole.  Basic Formula- A + B ---> AB  Examples-  2Na + Cl 2 → 2 NaCl (formation of table salt)  4 Fe + 3 O 2 → 2 Fe 2 O 3 (iron rusting)  

Single Displacement  An element trades places with another element in a compound.  Basic Formula- A + BC ---> AC + B  An example- magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas  Mg + 2 H 2 O ---> Mg(OH) 2 + H 2  

Double Displacement  Cations and Anions of two different molecules switch places two form to totally different compounds.  Basic Formula- AB + CD ---> AD + CB  An example- The reaction of lead nitrate with potassium iodide to form lead iodide and potassium nitrate  Pb(NO 3 ) KI ---> PbI KNO 3  

Bibliography  “Chemical Reaction Definition-”   “Chemical Reactions”   “Ten Signs of a Chemical Change”   “The Law of Conservation Mass”   “Law of Conservation Mass- Definition”   “Types of Chemical Reactions”   “Activation Energy”    “Combustion”   “Combustion Reactions” 

Bibliography Continued  “Chemical Decomposition”   “Chemical Synthesis”   “The Six Types of Chemical Reactions” 

Chemical Reaction Power Point By Ollie Auerbach