Writing And Balancing Equations
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Transcript Writing And Balancing Equations
Writing And Balancing
Equations
Chemistry
Dr. May
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 H2SO4 means 2 molecules of sulfuric 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
+ 2 HCl
ZnCl2 +
H2
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 + 2 HOH
Write Equation
Aluminum
hydroxide plus sulfuric acid
gives aluminum sulfate plus water
Aluminum = Al+3
Hydrogen = H+1
Hydroxide = OH1
Sulfate = SO42
Al(OH)3 + H2SO4 Al2(SO4)3 + H2O
Balance The Equation
Al(OH)3 + H2SO4
Al2(SO4)3 +
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
HOH
2 Al(OH)3 + 3 H2SO4
Al2(SO4)3 +
2 Al(OH)3 + 2 H2SO4
Al2(SO4)3 + 6 HOH
HOH
Write The Equation
Propane
burns to produce carbon
dioxide and water
C 3H 8
+
O2
CO2
+
H2O
The above skeleton equation must be balanced
Balance The Equation
C3H8
+
O2
CO2
+
First balance the carbons
C3H8 + O2 3 CO2
H2O
+
H2O
+
+
4 H2O
4 = 10
Next balance the hydrogens
C3H8 + O2 3 CO2
6
Finally balance the oxygens
C3H8
+
5 O2
2 x 5 = 10
3 CO2
+
4 H2O
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]