ChemCatalyst 2/1/121. 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. 4H2Oc. 5Be(C2H3O2)2

Balancing Chemical Equations

The Law of Conservation of Mass

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.

The Law of Conservation of Mass

Balancing Chemical Equations

Balancing a chemical equation means having the same number of atoms on your reactant side as you have on your products side.

H2 + O2 H2OH= 2O= 2

H= 2O= 1

This equation is not balanced because the Oxygen atoms are not equal

How do we balance?

To balance the chemical equation, you must add Coefficients in front of the chemical formulas in the equation.

You cannot add or change subscripts!5H2OCoefficie

nt Subscript

Balancing Step #1 Draw a line to separate the

REACTANTS from the Products For Each side determine number of

atoms for each element.H2 + O2 H2O

H= 2O= 2

H= 2O= 1

Balancing Step#2 Pick an element that is not equal on

both sides of the equation.

H2 + O2 H2O

H= 2O= 2

H= 2O= 1

Oxygen atoms are not equal !Ask you self what can I multiple the smaller Oxygen to get the larger oxygen?

By 2x

Balancing Step #3

Add a coefficient in front of the formula with that element and adjust your counts.H2 + O2 2H2O

H= 2O= 2

H= 2O= 1

By multiplying the oxygen on the products

side by a coefficient of two, we can change the number of

atoms

H= 4O=2

Balancing Step #4

Continue adding coefficients to get the same number of atoms of each element on each side.

2H2 + O2 2H2OH= 2O= 2

H= 4O=2

Now Hydrogen is not balance,

so repeat steps 2 and 3 to balance hydrogen!

H= 4O=2

Now we are balanced!

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!

2H2 + O2 2H2O

Lets Try Some Practice!

1. __Mg + __O2 ___MgO

2.__Ca + __O2 __CaO

3.__N2 + __H2 __NH3