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Writing And Balancing EquationsPowerPoint Presentation

Writing And Balancing Equations

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Presentation Transcript

The Road To Writing Sentences

- Know the alphabet
- Know vowels and consonants
- Know how to spell words
- Know the meaning of words
- Know sentence structure
- Know capitalization and punctuation

The Road To Writing Equations

- Know the atomic symbols
- Know oxidation numbers of elements
- Know the charge on polyatomic ions
- Be able to create the correct formulas
- Identify the reactants and products
- Balance the equation

The Language of Equations

Ca(OH)2 + H2SO4 CaSO4 + 2 H2O

- The equation above is like a sentence
- The compounds Ca(OH)2, H2SO4, CaSO4, and H2O are like correctly spelled and chosen words
- The elements Ca, O, H, and S are like the letters of the alphabet

Equations in English

Ca(OH)2 + H2SO4 CaSO4 + 2 H2O

- One molecule of calcium hydroxide plus one molecule of sulfuric acid yields one molecule of calcium sulfate plus two molecules of water.

Equations

Zn + 2 HCl ZnCl2 + H2

- On the left, Zn and HCl are reactants
- On the right, ZnCl2 and H2 are products
- The arrow () means “yields”
- The up arrow () indicated a gas product
- The 2 in front of HCl is a coefficient
- The small 2 to the right of H is a subscript

“Skeleton” Equation

- Identify the reaction
- Zinc reacts with hydrochloric acid to give zinc chloride and hydrogen gas

- Determine the correct formulas and write the “skeleton” (unbalanced) equation
- Zn + HCl ZnCl2 + H2

Coefficients

- A coefficient placed before a formula multiplies every atom in that formula by that number
2 H2SO4

- 2 H2SO4means 2 molecules ofsulfuric acid but also
- 4 H atoms, 2 S atoms, and 8 O atoms

Conservation Of Mass

- A balanced equation contains the same number of each kind of atom on each side of the equation
- The balanced equation obeys the
Law of Conservation of Mass

Balance The Equation

Zn + HCl ZnCl2 + H2

- Count atoms of each element on each side
- Balance each element by placing whole numbers (coefficients) in front of each formula as needed
Zn + HCl ZnCl2 + H2

2

Write Equation

- Calcium hydroxide reacts with sulfuric acid to give calcium sulfate and water

Calcium = Ca+2

Hydroxide = OH1

Hydrogen = H+1

Sulfate = SO42

Ca(OH)2 + H2SO4

CaSO4 + H2O

Balance Equation

Ca(OH)2 + H2SO4 CaSO4 + HOH

Count atoms on both sides

1Ca, 2OH, 2H, 1SO4

1Ca, 1OH, 1H, 1SO4

Balance the water

Ca(OH)2 + H2SO4 CaSO4 + HOH

2

Write Equation

- Aluminum hydroxide plus sulfuric acid gives aluminum sulfate plus water

Aluminum = Al+3 Hydroxide = OH1

Hydrogen = H+1 Sulfate = SO42

Al(OH)3 + H2SO4

Al2(SO4)3 + H2O

Balance The Equation

Al(OH)3 + H2SO4

Al2(SO4)3 + HOH

1 Al, 3 OH, 2 H, 1 SO4

2 Al, 3 SO4, 1 H, 1 OH

2 Al(OH)3 + H2SO4

Al2(SO4)3 + HOH

2 Al(OH)3 + 3 H2SO4

Al2(SO4)3 + HOH

2 Al(OH)3 + 2 H2SO4

Al2(SO4)3 + 6 HOH

Write The Equation

- Propane burns to produce carbon dioxide and water
C3H8 + O2 CO2 + H2O

The above skeleton equation must be balanced

Balance The Equation

C3H8 + O2 CO2 + H2O

- First balance the carbons
C3H8 + O2 3CO2 + H2O

- Next balance the hydrogens
C3H8 + O2 3 CO2 + 4H2O

- Finally balance the oxygens
C3H8 + 5 O2 3 CO2 + 4 H2O

6 + 4 = 10

2 x 5 = 10

Chemical Equations

- Chemical equations are the short hand description of a chemical reaction
- It tells us:
- The reactants and products
- The formulas of the reactants and products
- The number of molecules of reactants and products
- The number of atoms of each element
- The number of moles of each substance

The End

- This presentation was created for the benefit of our students by the Science Department at Howard High School of Technology
- Please send suggestions and comments to [email protected]

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