Balancing Chemical equations Pages 170 - 174

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# Balancing Chemical equations Pages 170 - 174 - PowerPoint PPT Presentation

Balancing Chemical equations Pages 170 - 174. The “Law of Conservation of Mass” states that: the total mass of the reactants in a chemical equation is equal to the total mass of the products.

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### Balancing Chemical equationsPages 170 - 174

The “Law of Conservation of Mass” states that: the total mass of the reactants in a chemical equation is equal to the total mass of the products.

To state the law simply: in a chemical reaction atoms are neither created or destroyed. They are only rearranged. Thus, there must be an equal number of atoms of each element on each side of the arrow in the equation.

An equation that has an equal number of atoms of each element on each side of the arrow is a balanced equation.
• Example: K + S -> K2S
• In this example one atom of potassium is chemically combining with one atom of sulfur to produce a new compound called potassium sulfide.
Example: K + S -> K2S
• The new compound contains 2 atoms of potassium and one atom of sulfur. An atom of potassium has been created. THIS IS NOT POSSIBLE!! Therefore you must have had two atoms of potassium to begin with.
• 2K + S -> K2S
• The coefficient 2 must be added to K on the left side of the arrow.
How to balance an equationBalancing an equation is a process that requires patience. It can be done in 3 steps
• Find the valence number on the periodic table then use them to predict the subscripts for the new product.
• Count the atoms on each side of the arrows and place coefficients in front of the appropriate elements to balance. Note – never change a subscript to balance.

Al3++ S2- -> Al2S3

reactant reactant product

2Al + 3S -> Al2S3

3. Count the number and types of atoms on each side of the arrows.

Two aluminum plus there sulfur produce two aluminum, three sulfur

Aluminum plus sulfur produce aluminum sulfide

Names and Formulas for polyatomic Ions Page 159
• Polyatomic ions consist of two or more different non metals , which are joined together by a covalent bond.
• Ammonium ion NH4+
• Hydroxide ion OH-
• Carbonate CO32-
• Nitrate CO32-
• Sulfate SO42-
• Hydrogen carbonate HCO3-
• Hydrogen sulfate HSO4-
• Phosphate PO43-
Diatomic Molecules
• There are 7 elements that do not like to be left alone. They form a covalent bond with their twin. I call them my HOBrFINCl ‘s
• H2
• O2
• Br2
• F2
• I2
• N2
• Cl2