Chemical Reactions

definition  Process in which one or more substances are converted into a new substance with different physical and chemical properties  In a chemical reaction, the atoms of the starting substance (reactants) are rearranged to produce a new substance (products).  The law of conservation of mass/matter is obeyed. This law states mass/matter can’t be created or destroyed, it simply changes form.

Clues a chemical reaction has occurred. 1. Energy is absorbed or released (Δ temp) 2. Change in color 3. Precipitate (solid) is formed 4. Gas (bubbles) are formed 5. Change in odor

Representing Chemical Reactions  Word Equation 1.Iron and chloride react to produce iron (III) chloride 2.The reaction between carbon and sulfur yields carbon disulfide  Skeleton Equation 1.Fe + Cl 2 -  FeCl 3 2.C(s) + S(s) -  CS 2

Cont’d  Chemical Equation- must be balanced because of the law of conservation of mass.  Same # of atoms of each element on both sides of the equation (arrow)

Method for balancing Equation 1. Write skeleton equation 2. Count the atoms of each element on reactant 3. Count the atoms of each element on product 4. Use coefficients to make the number of atoms of each element equal on both sides of equation 5. Write coefficients in their lowest possible ratio 6. If an element is in more than one compound on the same side of equation, wait until you have balanced all the other elements