1. What does The Law of Conservation of Mass State? 2. How many atoms of each elements do you have in the following compounds: a. Mg(OH) 2 b. 4H 2 O c. 5Be(C 2 H 3 O 2 ) 2

The Law of Conservation of Mass

 Mass (atoms) can not be created or destroyed during a chemical reaction. mass of the reactants = mass of the products  In order for the Law of Conservation of Mass to apply there must be the same number of atoms on each side of the chemical reaction.

 Balancing a chemical equation means having the same number of atoms on your reactant side as you have on your products side. H 2 + O 2  H 2 O H= 2 O= 2 H= 2 O= 1 This equation is not balanced because the Oxygen atoms are not equal

 To balance the chemical equation, you must add Coefficients in front of the chemical formulas in the equation.  You cannot add or change subscripts! 5H 2 O Coefficient

 Draw a line to separate the REACTANTS from the Products  For Each side determine number of atoms for each element. H 2 + O 2  H 2 O H= 2 O= 2 H= 2 O= 1

 Pick an element that is not equal on both sides of the equation. H 2 + O 2  H 2 O H= 2 O= 2 H= 2 O= 1 Oxygen atoms are not equal ! Ask you self what can I multiple the smaller Oxygen to get the larger oxygen? By 2x

 Add a coefficient in front of the formula with that element and adjust your counts. H 2 + O 2  2H 2 O H= 2 O= 2 H= 2 O= 1 By multiplying the oxygen on the products side by a coefficient of two, we can change the number of atoms H= 4 O=2

 Continue adding coefficients to get the same number of atoms of each element on each side. 2H 2 + O 2  2H 2 O H= 2 O= 2 H= 4 O=2 Now Hydrogen is not balance, so repeat steps 2 and 3 to balance hydrogen! H= 4 O=2

 The number of hydrogen atoms and oxygen are equal on each side of the chemical equations! Its like a fun puzzle! DON’T GIVE UP! 2H 2 + O 2  2H 2 O

1. __Mg + __O 2  ___MgO 2. __Ca + __O 2  __CaO 3. __N 2 + __H 2  __NH 3