 A chemical change: any change in which a new substance is formed. Evidence of a Chemical Change:  Release of energy as heat  Release of energy as light  Change in color  Formation of a gas  Change in odor

4 types of chemical reactions 1. Synthesis reaction 2. Decomposition reaction 3. Single-replacement reaction 4. Double- replacement reaction

 Synthesis reactions- (aka Formation reactions) in which two or more substances combine to form a single compound.  A + B  AB  where A and B represent elements

Elements that form ionic compounds: Sodium metal and chlorine gas combine to form sodium chloride.  2Na + Cl 2  2NaCl Elements that form covalent compounds: Nitrogen gas and oxygen gas join to form dinitrogen monoxide.  2N 2 + O 2  2N 2 O

 Decomposition reactions-is a reaction in which a single compound breaks down to form two or more simpler substances.  AB  A + B where A and B represent elements

 Covalent compounds may decompose into elements, like the following:  2H 2 O  2H 2 + O 2  By running electricity through water, the water molecules decompose into hydrogen and oxygen gases.

 Example: 2HgO General: AB  A + B  OHg O OO +

 Decomposition reaction 

 Single replacement reactions- replace one element from a compound with another element.  A + BC  B + AC where A is a metal, or  A + BC  C + BA where A is a non-metal

 A compound and an element react, and the element switches places with part of the original compound.  Example: Zn + CuCl 2 General: AB + C  AC + B Cl Zn Cu +  Zn Cl Cu +

 Double replacement reactions- is a reaction in which ions in two compounds switch places. AB + CD  AD + CB

 The swapping of elements between 2 compounds that react together form two new compounds.  Example: MgO + CaS S O  Mg Ca + O S Mg Ca +

 types of chemical reactions    Chemical reaction song  

 Combustion - is a reaction between a fuel (organic) in the presence of oxygen and an initial starter of energy (heat) forming carbon dioxide + water and energy (heat or light).