By: Seamus O’Brien

 In a chemical reaction the elements bond to each other through the taking or sharing of valence electrons.  During chemical reactions energy changes one form of matter into another.  The elements going into the chemical reactions are called reactants. After the elements have reacted they create a product.  Signs of a chemical reaction are bubbling, change in color, or a change in temperature. ps/chm/100/dgodambe/thedisk/chemrxn/signs2.htm ps/chm/100/dgodambe/thedisk/chemrxn/signs2.htm  The law of conservation of matter states that matter cannot be created nor destroyed. During chemical reactions matter seems to be created or destroyed, but really the atoms or molecules are just being rearranged.  Pictures

 Every substance has energy from its electrons. Most things have potential energy as well.  Potential energy is the energy stored in something, this energy has the potential to be turned into other types of energy, hence the name “potential energy”.  To start a chemical reaction you will need some form of energy. This is called activation energy. This type of energy is needed because sometimes the elements need a little push to collide.  Reactions that release heat, light or sound are exothermic reactions, they can occur spontaneously. Ex) the mixing or sodium and chlorine combine to make table salt.  Endothermic reactions absorb energy instead of producing it. These decrease in temperature. Ex) Photosynthesis  

Synthesis, Decomposition, Combustion, Single Replacement, and Double replacement.

 Synthesis is when two reactants are put together to form one product.  The basic form is: A + B  AB A and B are elements or compounds, and AB is the products that the elements or compounds create. A and B are known as reactants.  2Na + Cl 2  2 NaCl is the formula to form of table salt.  4 Fe + 3 O 2  2 Fe 2 O 3 is the formula of iron rusting. o

o Decomposition is the splitting of a compound into two different elements. o The basic form of decomposition is: AB  A + B  AB is a chemical compound.  A and B are the elements that are forms after decomposition has occurred.  2H 2 O 2  2H 2 O + O 2 is and example of hydrogen peroxide, which will decompose into water and oxygen. o H 2 CO 3  H 2 O + CO 2 is carbonic acid it will decompose over time into carbon dioxide and water. o

 Combustion is a series of exothermic chemical reactions involving a type fuel and an oxidant.  These reactions give off heat, light, or both usually in flames or a glow.  There is no basic formula for combustion, however it will always contain oxygen in it.  2H 2 + O 2  2H 2 O(g) + heat, is an example of combustion. This is the combustion of hydrogen and oxygen. The result is water vapor. 

 Single replacement is when an ion or an element switch from one compound to another.  The basic form is A + BX  AX + B. Single replacement will occur if A is more reactive than B. A and B must either be metals, this makes X an anion, or A and B can be halogens, this will make X a cation.  Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) is an example of single replacement. In this reaction magnesium, and hydrochloric acid, form magnesium chloride, and hydrogen.  The guy in the orange shirt steals the date of the other guy. So, a part of one of the reactants trades places and is in a different place among the products.

 Double replacement involves the exchange of bonds between the two reacting chemical species.  It creates products with similar or identical bonding affiliations.  The formula for double replacement is AB + CD  AD + CB These chemical species can either be ionic or covalent.  HCl(aq) + NaOH(aq)  NaCl(aq) + H 2 O(l) is an example of double replacement. This reaction creates a solution of salt and water. 

 Chemical Reactions  Signs of a Chemical Reaction ps/chm/100/dgodambe/thedisk/chemrxn/signs2.htm ps/chm/100/dgodambe/thedisk/chemrxn/signs2.htm  Law of Conservation of Matter onservation/LawofConservation.htm onservation/LawofConservation.htm  Endothermic and Exothermic Reactions  Chemical Synthesis  Chemical decomposition  Combustion  Single Displacement Reaction  Metathesis Reaction