 # Law of Conservation of Mass

Law of Conservation of Mass

A chemical equation is

a representation of a chemical reaction that uses symbols to show the relationship between the reactants and the products

From Reactants to Products

Reactants –

a substance or molecule that participates in a chemical reaction

Products –

the substance that forms in a chemical reaction

Using Figure 5 from page 394, label the parts of a Chemical Equation

C   +     O2         ®    CO2

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Page 395The Reason Equations Must Be Balanced

Atoms are never ______lost_____________ or _____gained________ in a chemical reaction.  They are just rearranged.  Every atom in the  reactants_______ becomes part of the ____products____.  When writing a __chemical___ __equation__, make sure the number of atoms of each element in the reactants ____equals___ the number of atoms of those elements in the products.  This is called ___balancing____ the equation.

Law of Conservation of Mass :

mass cannot be created or destroyed in ordinary chemical and physical changes

Let’s Practice! – Use the instructions below to complete A. and B. below.

1)Find the mass or number of atoms in the reactants and products.

2)Explain whether or not the chemical equation follows the law of conservation

of mass.

A.  Making a PB&J Sandwich!

2 slices of bread + 1 tablespoon-Peanut Butter + 1 tablespoon-Jelly ®   PB&J sandwich

(30 g)     +           (14 g)         +     (14 g)              =   40 g

Does it follow the Law of Conservation of Mass?

No because the mass in the product does not equal the mass of the reactants (bread, PB, and Jelly).

B.  2Al + 3Cl2    →          2AlCl3

# of Al =     2          # of Al =2

# of Cl =       6        # of Cl  =  6

Does it follow the Law of Conservation of Mass?

Yes, the number of atoms of each element are the same in the products and the reactants.