Balancing Equations Pre Ap

Chemical Equations & Balancing Equations

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Chemical Reactions occur when there is a chemical change. Indicators for a chemical change    

Energy change (heat or light) Production of Gas Formation of a solid (precipitate) Color Change

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A properly written chemical equation must have the following requirements: 

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The equation must represent known facts The equation must contain the correct formulas for the reactants and products The law of conservation of mass must be satisfied – the mass of the

Writing Chemical Equations 

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In a chemical equation, formulas of reactants (left side) & products (right side) are connected by an arrow. (Read the arrow as “yields”.) Chemical equations describe chemical reactions & include symbols to show the phase of each chemical involved. 

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(s) = solids, (l) = liquids, (g) = gaseous, (aq) = aqueous or in water. Bonds are broken & reformed in equations-atoms are rearranged, but matter is not created or destroyed.

More on Chemical Equations 

Catalysts—speed up chemical reactions. Catalysts are not changed by a reaction, they can be removed after the reaction and the same amount will be there as at the start. 

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Catalysts are written over the arrow. Heat, temperature, & pressure may also be written over the arrow.

Double arrows indicate an equilibrium— the reaction can go in both directions. Numbers in front of the chemicals are coefficients. They show the ratio of the

Steps to Successful Balancing 1.) Equations must have the same amount of each type of atom on each side of the arrow. (Law of Conservation of Mass) Ex. 2H2 + O2 2H2O H4

O2

H4

O2

2.) Count how many of each element is on the reactant side. 3.) Count how many of each element is on the product side.

Steps to Successful Balancing 4.) If an element on the reactant side does not equal the same amount on the products side, multiply by an amount such that they become equal. 5.) Continue multiplying until all elements equal the same amount on both the reactant and product side.

Helpful Hints 

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Start balancing your compounds first. Leave Oxygen and Hydrogen until the end to balance. Leave elements until the end to balance.

Example #1 BaS + NaI -> BaI + Na S 2

Reactants: 1 – Ba 1–S 1 – Na 1–I

2

Products: 1 – Ba 1–S 2 – Na 2–I

Example #1 BaS +2 NaI -> BaI + Na S 2

Reactants: 1 – Ba 1–S 1 – Na x 2 2 1–I

Products: 1 – Ba 1–S 2 – Na 2–I

2

Example #1 BaS + 2NaI -> BaI + Na S 2

Reactants: 1 – Ba 1–S 2 – Na 2–I

2

Products: 1 – Ba 1–S 2 – Na 2–I

Example #2 KF + CaBr -> CaF + KBr 2

Reactants: 1–K 1–F 1 – Ca 2 – Br

2

Products: 1–K 2–F 1 – Ca 1 – Br

Example #2 2 KF + CaBr2 -> CaF2 + 2 KBr

Reactants: 2 1–K 1–Fx2 1 – Ca 2 – Br

2

Products: 1–K 2–F 1 – Ca 1 – Br x 2

Example #2 2KF + CaBr -> CaF + 2KBr 2

Reactants: 2–K 2–F 1 – Ca 2 – Br

2

Products: 2–K 2–F 1 – Ca 2 – Br

Example #3 AlCl3 + K2O -> Al O + KCl 2

Reactants: 1 – Al 3 – Cl 2–K 1–O

3

Products: 2 – Al 1 – Cl 1–K 3–O

Example #3 2 AlCl3 + 3 K2O -> Al2O3 + 6KCl

Reactants: 1 – Al x 2 6 3 – Cl 6 2–K 1–Ox3

Products: 2 – Al 1 – Cl X 6 1–K X6 3–O

Example #3 2AlCl3 + 3K2O -> Al O + 6KCl 2

Reactants: 2 – Al 6 – Cl 6–K 3–O

3

Products: 2 – Al 6 – Cl 6–K 3–O

Ex. 4 NaCl(aq) + Al2(SO4)3(aq) -> AlCl3(aq)+ Na2SO4(aq) 6NaCl(aq) + Al2(SO4)3(aq) -> 2AlCl3(aq)+ 3Na2SO4(aq)

Balancing Combustion Reactions Combustion of hydrocarbons consist of a an organic compound reacting with oxygen to produce CO2 and H 2O Ex: C3H8 + O2 -> CO2 + H2O 1st balance C’s 2nd balance H’s

Balancing Combustion cont. Try another one: C6H14 + O2 -> CO2 + H2O

What is the most sparsely populated country in the Western Hemisphere? Iceland w/ 3.0 people per square km (US is about 30 people)