Transcript Chemical Reactions & Balancing Equations

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Chemical
Reactions &
Balancing
Equations
2
Chemical Reactions
2 Parts:
Reactants: substances at the start
Products: substances at the end

The reactants turn into the products.
Reactants  Products
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Equation Format:
“+”
means “reacts with” or “and”
“” means “yields” or “forms”
Reactants written on LEFT side
Products written on RIGHT side
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Inquiry Lab

Effervescent Tablet –Na(HCO3) & C6H8O7
NaHCO3+ C6H8O7  Na3C6H8O7 + H2O + CO2
sodium + citric  sodium + water + carbon
bicarbonate acid
citrate
dioxide
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In a Chemical Reaction
The way atoms are joined is changed
 Atoms are neither created nor destroyed.

–This is the Law of Conservation of
Matter

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Balanced Equation:
– Each element has same # of atoms on
both sides of the equation.
C
C
+
O
O
+
O2


O C
O
CO2
This equation is already balanced
– same number of atoms of each type of
element on each side
 What if it isn’t balanced already?

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If it is NOT Balanced Already…
C
+
C +
O
O

O2

C
O
CO
• This is called a skeletal reaction
• Shows all the reactants and products
• Does not show balanced quantities
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Cooking Analogy
for Chemical Reactions:
 Skeletal
reaction:
– Ingredients & description of meal
 Balanced reaction:
– Exact recipe
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Skeletal Reaction  Balanced Equation
C
+
O
O

C
O
C
O
• Add molecules until there is an equal
number of atoms on both sides.
• Use only molecules or atoms already in
the formulas
• No new compounds used or created
• Start with the element you need more of!
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Skeletal Reaction  Balanced Equation
C
1C
+
O
O
O2

C
O
C
O
2C & 2O
• The 2 subscript on Oxygen means there
are 2 of them in the molecule.
• Still not balanced  need 1 more C on the
reactant side.
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C
+
C
2C
O
O

C
O
C
O
O2

2C & 2O
O2

2CO
Equation:
2C
12
+
C
+
C
O
O

C
O
C
O
2C + O2  2CO
Coefficient:
•Large Number left of the compound formula.
•Represents the number of molecules/atoms
• Helps to balance the equations
• makes # of atoms on left side = # on right side
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• Coefficients & Subscripts on the same
molecule
• The numbers must be multiplied to
determine the number of atoms of
that element.
2C
2C
+
2O2
4O

2CO2
2C & 4O
• Notice the subscript only applies to the
element it is next to!
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