Balancing Chemical Equations TEKS 8.5D recognize that chemical formulas are used to identify substances and determine the number of atoms of each element in chemical formulas containing subscripts TEKS 8.5F recognize whether a chemical equation containing coefficients is balanced or not and how that relates to the law of conservation of mass

occurs when the chemical bonds between elements are formed or broken. A chemical reaction er/view/assetGuid/12FC25F B B8DB4A6

This requires a gain or loss of energy.

is a short, simple way to describe a chemical reactions using symbols and formulas instead of words. A chemical equation

are the substances you begin with. Reactants

Fe + 2 HCl FeCl 2 + H 2 reactants products yield sign

Products are the substances you end with.

The yield sign points to the Product. Fe + 2 HCl FeCl 2 + H 2 reactants products yield sign

During a chemical reaction, the atoms rearrange to form new bonds between atoms.

The products formed in a chemical reaction have different properties from the reactants.

Reading a chemical equation: 1 atom of iron reacts with 2 molecules of hydrochloric acid to yield 1 molecule of Iron chloride and 1 molecule of hydrogen Fe+2HClFeCl 2 +H 2

Law of Conservation of Mass Mass can neither be created or destroyed.

Law of Conservation of Mass Before and after a chemical reaction…… atoms cannot be created or destroyed.

Law of Conservation of Mass So the number of atoms at the beginning and end MUST equal.

Law of Conservation of Mass So the mass at the beginning and end MUST equal.

What if the number of atoms in the reactants does not match the number in the products?

C 3 H 8 + O 2 CO 2 + H 2 O mass =76 gramsmass = 62 grams 3-carbon1-carbon 3-carbon1-carbon 8-hydrogen2-hydrogen 8-hydrogen2-hydrogen 2-oxygen3-oxygen 2-oxygen3-oxygen It needs to be balanced!

The Law of Conservation of Mass states that the number of each atom and masses must be equal on both sides of the yield sign.

Rules for Balancing Equations

Chemical formulas CANNOT be changed! H20H20 O2O2 NaCL C 6 H 12 O 6

Subscripts CANNOT be changed! H2OH2O Don’t change me!

Coefficients CAN be added or changed before an element or molecule. H 2H H 2 0 2H 2 0

C 3 H 8 + O 2 => CO 2 + H 2 O 534 Add coefficients to the equation to balance the number of atoms

C 3 H 8 + 5O 2 => 3CO 2 + 4H 2 O 3-carbon8-hydrogen10-oxygen Now the atoms are equal, so the mass is equal.

What is used to balance equations? Coefficients