Transcript Balancing Equations

Balancing Equations
D. Crowley, 2007
Balancing Equations
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To be able to balance equations
Symbols
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Remember, each element has its own symbol(s) - all found in
the periodic table
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Every symbol begins with a capital, and may have one or
more other non-capital letters which follow
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E.g.
Oxygen = O
Nitrogen = N
Sodium = Na
Magnesium = Mg
Copper = Cu
Balancing
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A chemical reaction can be described by the process
reactants → products
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E.g. magnesium reacts with oxygen, producing magnesium
oxide
magnesium + oxygen → magnesium oxide
2Mg + O2 → 2MgO
Balancing
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It is key you know how to balance the equations!
Remember: there must always be the same number of atoms
on both sides
Numbers can only be put in front of the formula when it is
needed
Magnesium Oxide
Look at the following reaction
magnesium + oxygen → magnesium oxide
2Mg + O2 → MgO
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You’ll notice, that there are more red and blue circles on the
left hand side, than there are on the right
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To balance this, we can add a number in front of the right
hand side
2Mg + O2 → 2MgO
Water
Look at the following reaction
hydrogen + oxygen → water
H 2 + O2 → H 2 O
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Again there is a problem – this time we have an oxygen atom
missing from the right hand side
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To balance this, we can add a number in front of the right
hand side
H2 + O2 → 2H2O
Water
But this is still unbalanced!
hydrogen + oxygen → water
H2 + O2 → 2H2O
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Finally, we can add a number in front of the hydrogen on the
left hand side, to balance this up
2H2 + O2 → 2H2O
Example
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Look at the following reaction:
H2SO4 + NaOH → Na2SO4 + H2O

The formulas are correct, but the number of
atoms on the left are different from those on
the right
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Remember: we can only put numbers in
front of the symbols…
Balancing
H2SO4 + NaOH → Na2SO4 + H20

In the equation, there are more H atoms on the left, than there
are on the right
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So we can add a 2 in front of the H2O on the right side
H2SO4 + NaOH → Na2SO4 + 2H20
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Now we have too many H and O atoms on the right hand side,
so we can put a 2 in front of the NaOH on the left side
H2SO4 + 2NaOH → Na2SO4 + 2H20
Now everything balances!
Questions
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Write a word equation for what happens when copper burns
How many reactants are there in this reaction?
What are these reactants?
What is the product of the reaction?
When you find the mass at the end of the experiment, what
chemical are you finding the mass of?
Answers
 copper + oxygen → copper oxide
 2 Reactants
 Reactants: copper + oxygen
 Product: copper oxide
 You are calculating the mass of the copper oxide
Balance The Equations
H2 + O2 → H2O
H2 + N2 → NH3
C3H8 + O2 → CO2 + H2O
Al + CuO → Al2O3 + Cu
K2O + H2O → KOH
CaCl2 + AgNO3 → AgCl + Ca(NO3)2
Balance The Equations
2H2 + O2 → 2H2O
3H2 + N2 → 2NH3
C3H8 + 5O2 → 3CO2 + 4H2O
2Al + 3CuO → Al2O3 + 3Cu
K2O + H2O → 2KOH
CaCl2 + 2AgNO3 → 2AgCl + Ca(NO3)2