Chemical Reactions Conservation of Mass

Law of Conservation of Mass In a chemical change, matter is neither created or destroyed. Mass of Reactants = Mass of Products # of Reactant Atoms = # of Product Atoms

Conservation of Mass

Counting Atoms

Atoms are Conserved in a Chemical Reaction The identities (formulas) of the compounds must never be changed in balancing chemical equations. DO NOT change the Subscripts. You may only change the coefficients in an equation to balance the equation.

Steps To Balancing an Equation Here are the basic steps to follow when balancing equations. You should always use pencil when balancing equation so that you can erase any mistakes. 1st  Count the atoms of each element on each side of the arrow in an equation. Ex. CH4 + O2  CO2 + H2O C = 1 C = 1 H = 4 H = 2 O = 2 0 = 3

Steps To Balancing an Equation 2nd We need to add compounds to get equal numbers of each element. You can only add whole amounts of a molecule. Ex. CH4 + O2 + O2  CO2 + H2O + H2O C = 1 C = 1 H = 4 H = 4 O = 4 O = 4

Steps To Balancing an Equation The correct way to write this is to put a coefficient to represent multiple molecules or formula units. - A coefficient is placed before a molecule. - A coefficient pertains to every element in the compound, regardless of parenthesis. Ex. CH4 + 2O2  CO2 + 2H2O C = 1 C = 1 H = 4 H = 4 O = 4 O = 4 The equation is now balanced because there are equal amounts of carbon, hydrogen, and oxygen on the reactant side and on the product side.

Na + Br2  NaBr

Ca(OH)2 + HNO3  Ca(NO3)2 + H2O

Al2O3  Al + O2