Chemical reactions

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Chemical reactions

• How to figure them out.

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4 types of chemical reactions
Synthesis reaction
Single replacement reaction
Double replacement reaction
Decomposition reaction
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Things to know

• Diatomic molecules H2, N2, O2, F2, Cl2,
  Br2 , I2
• All molecules and compounds in nature want to
  have a neutral charge.

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Synthesis reaction
A B AB
Two separate chemicals are joined together to
form a compound or molecule.
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Synthesis reactionstep 1 Figure out the
products of the reaction.
Na(s) Cl(g) flame
Na(s) Cl(g) flame NaCl
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Synthesis reactionstep 2 Find each chemicals
charges.
Na(s) Cl(g) flame NaCl(s)
Use the periodic table to find the charge for
each element.
Nao(s) Clo(g) flame Na1Cl-1(s)
Nao and Clo are both neutral because all
chemicals, by themselves, are neutral.
Na is in column 1. Cl is in column 7. Chlorine
takes the outer most electron of sodium. Both
then have 8 outer most electrons. The ions of Na
and Cl are more stable when they are bonded.
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Synthesis reaction step 3 Find any diatomic
elements.
Na(s) Cl(g) flame NaCl (s)
Check the periodic table to see if each element
exists as a diatomic molecule. See slide 4.
Nao(s) Cl2o(g) flame Na1Cl-1(s)
Note diatomic 2 atoms bonded in one molecule.
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Synthesis reaction step 4 Make each molecule
have a charge of zero.
Nao(s) Cl2o(g) flame Na1Cl-1(s)
The Na1Cl-1compound has a total charge of zero.

No adjustments are necessary.
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Synthesis reaction Step 5 Balance the two
sides of the chemical equation.
Nao(s) Cl2o(g) flame Na1Cl-1(s)
There is not the same amount of Cl on both sides
of the chemical reaction.
Nao(s) Cl2o(g) flame 2Na1Cl-1(s)
The Cl is balanced, but the amount of Na on both
sides of the chemical equation is not the same.
2Nao(s) Cl2o(g) flame2Na1Cl-1(s)
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Synthesis reaction
Examples
hydrogen oxygen makes water
iron oxygen makes iron oxide (rust)
sodium oxygen makes sodium oxide
magnesium oxygen makes magnesium oxide
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Single replacement reaction
A BC AC B or
A BC BA C
One chemical (A) replaces one of the parts of the
molecule ( B or C).
If A and B can both have a positive charge then A
will replace B. If A and C can both have a
negative charge then A will replace C.
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Single replacement reaction step 1 Figure out
the products of the reaction.
Fe(s) CuSO4(aq)
Fe(s) CuSO4(aq) Cu FeSO4
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Single replacement reaction step 2 Find each
chemicals charges.
Fe(s) CuSO4(aq) Cu(s) FeSO4(aq)
Use the periodic table to find the charge for
each element and the one polyatomic ion.
Feo(s) Cu2SO4-2(aq) Cuo(s) Fe3SO4-2(aq)
Fe(s) and Cu(s) are both neutral because all
chemicals, by themselves, are neutral.
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Single replacement reactionstep 3 Find any
diatomic elements.
Check slide 4 to see if any of the elements are
diatomic (come in pairs).
There are no diatomic elements for this reaction.
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Single replacement reaction step 4 Make each
compound have a charge of zero.
Feo Cu2SO4-2 Cuo Fe3(SO4-2)

• The chemical reaction has one compound which does
  not have a total charge of zero.
• Fe3 has a charge of 3, but (SO4-2) has a
  charge of -2. They do not total zero. A
  combination has to be found to make the compound
  have a total charge equal to zero.
• If you have two Fe ions the total positive charge
  is 6. It you have three SO4 ions the total
  negative charge is -6. Fe32(SO4-2)3 has a
  neutral charge.

Feo Cu2SO4-2 Cuo Fe32(SO4-2)3
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Single Replacement Reaction Step 5 Balance
the two sides of the chemical equation.
Feo Cu2SO4-2 Cuo Fe32(SO4-2)3
There is not the same amount of Fe or SO4 on
both sides of the reaction.
2Feo 3Cu2SO4-2 Cuo Fe32(SO4-2)3
The Fe and SO4 are balanced, but now the Cu on
both sides are not the same.
2Feo 3Cu2SO4-2 3Cuo
Fe32(SO4-2)3
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Single replacement reaction
Examples
iron copper sulfate makes copper iron sulfate
copper silver nitrate silver
copper nitrate
sodium water hydrogen sodium
hydroxide
aluminum copper sulfate makes copper
aluminum sulfate
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Double replacement reaction
The elements with a positive charge (A) and (C)
switch places.
The exact same compounds would result if we said
that the two elements with negative charges
switch places.
This reaction happens only if the products are
more stable than the reactants.
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Double replacement reaction
Step 1 Figure out the products of the
reaction.
Pb(NO3)(aq) NaI(aq)
Pb(NO3)(aq) NaI(aq) NaNO3
PbI
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Double replacement reaction step 2 Find each
chemicals charges.
Pb(NO3)(aq) NaI (aq) NaNO3
PbI
Use the periodic table to find the charge for
each ion and the polyatomic ion.
Pb2(NO3) -1(aq) Na 1 I -1(aq)
Na 1 NO3 -1 Pb 2 I -1
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Double replacement reaction step 3 Find any
diatomic elements.
Check slide 4 to see if there is an element
which exists as a diatomic molecule.
Pb2(NO3) -1(aq) Na 1 I -1(aq)
Na 1 NO3 -1 Pb 2 I -1
There are none for this reaction.
It may look like iodine (I) would be a possible
element to be diatomic, but it is not by itself.
It is part of a compound on both sides of the
chemical reaction.
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Double replacement reaction step 4 Make each
compound have a charge of zero.
Pb2(NO3)-1 Na1 I-1 Na1
NO3-1 Pb2 I-1
The lead nitrate and lead iodide compounds do not
have a charge of zero.
Pb2(NO3)2-1 Na1 I-1 Na1
NO3-1 Pb2 I2-1
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Double replacement reaction Step 5 Balance
the two sides of the chemical equation.
Pb2(NO3) 2-1 Na1 I -1
Na1 NO3 -1 Pb 2 I2-1
There is not the same amount of (NO3) and I on
both sides of the reaction.
Pb2(NO3) 2-1 2Na1 I -1
2Na1 NO3 -1 Pb 2 I2-1
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Double replacement reaction
Examples
silver nitrate sodium chloride silver
chloride sodium nitrate
silver nitrate sodium iodide silver iodide
sodium nitrate
silver nitrate potassium iodide silver iodide
potassium nitrate
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Decomposition reaction
AB A B
A molecule/compound is divided into its separate
chemicals.
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Decomposition reaction step 1 Figure out the
products of the reaction.
NaCl(s) electricity
NaCl(s) electricity
Na(s) Cl(g)
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Decomposition reaction step 2 Find each
chemicals charges.
NaCl(s) Na
Cl
Use the periodic table to find the charge for
each ion and element.
Na1Cl-1(s) Nao
Clo
Na and Cl are both neutral because all elements,
by themselves, are neutral.
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Decomposition reactionstep 3 Find any
diatomic elements.
NaCl(s) electricity
Na(s) Cl(g)
Chlorine is an element which forms a molecule
with 2 atoms.
NaCl(s) electricity
Na(s) Cl2(g)
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Decomposition reaction step 4 Make each
molecule have a charge of zero.
Na1Cl-1(s) electricity Nao(s)
Cl2o(g)
Na1Cl-1(s) electricity Nao(s)
Cl2o(g)
No changes are necessary. All the molecules have
a neutral charge.
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Decomposition reaction Step 5 Balance the two
sides of the chemical equation.
Na1Cl-1(s) electricity
Nao(s) Cl2o(g)
There is not the same amount of chlorine (Cl) on
both sides of the chemical reaction.
2Na1Cl-1(s) electricity
Nao(s) Cl2o(g)
There is not the same amount of sodium (Na) on
both sides of the chemical reaction.
2Na1Cl-1(s) electricity
2Nao(s) Cl2o(g)
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Decomposition reaction
Examples
Water is divided into hydrogen gas and oxygen
gas. Salt is divided into sodium metal and
chlorine gas.
H2CO3(l) breaks apart into water and carbon
dioxide.
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Complete the two chemical reactions.

• Fe2O3(s) C(s)
• Rust coke intense heat
• NaCl(S)
• Salt electricity

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Test your understanding
List the four types of chemical reactions.