Chemical Equations & Balancing

What is a chemical equation?

• A standard way to describe a chemical reaction.–This means that scientists worldwide

use this system.

• Show the number and combinations of elements & compounds involved in the reaction.

Chemical Equations …• 2 Parts to a chemical equation:

– Reactants = original substance(s) (substances before any reaction occurs)

– Products = created during the reaction (ending substances)

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General Chemical Equations:

Reactant + Reactant Product + Product

• Not all reactions have 2 reactants and 2 products (could be one or more for each).

Reactantswritten before

the arrow.

Productswritten afterthe arrow.

Arrow representschemical reaction.

For example: Label the reactants and products in this equation.

• How do you say this?

Sodium and chlorine react to form sodium chloride.

2Na + Cl2 2NaCl

Reactants Product

In chemical reactions, the number and kinds of elements are always the same!

Chemical Equations also show Conservation of Mass:

• There must be the same amount of each element in the reactants as in the products (although the element could be part of different compounds). http://media.photobucket.com/image/balance%20scales/

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Coefficients:

• Used to show conservation of mass in a chemical equation.

• Whole number put in front of a reactant or product to show a balanced chemical equation.

2Na + Cl2 2NaCl

• Multiplies the element(s) found in that specific reactant or product.

Balancing Chemical Equations:

• Write each reactant and product. (Remember how ions form chemical bonds.)

• Add coefficients to change the number of atoms within a substance.

• Never change the subscripts!

2 H2O2 2 H2O + O2a. Reactants?

b. H in reactants?

c. H in products?

d. O in reactants?

e. O in products?

f. Mass conserved? Why?

g. Without coefficients – conservation?

H

O

4 =

4 =

H = 2 X 2 = 4

H = 2 X 2 = 4

= 4

= 4

O = 2 X 2 = 4

O = 2 + 2 = 4

YES!

WhenReactants = Products

then massis conserved!

H2O2 H2O + O2

= 2

= 3

2 =

2 =

Does NOT showConservation ofMass because

Reactants do NOTequal Products.