Help with predicting products

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CHEMICAL REACTIONS TUTORIAL
Let’s get started!!
Goals
In this tutorial, you will learn…
 How to recognize 3 of the 5 types of reactions
 Predict the products of reactions when only
given the reactants
What are the 5 types of
reactions?
Synthesis
Double
replacement
Single
replacement
Decomposition
Combustion
Which 3 will be we learning
about??
Synthesis
Decomposition
Combustion
SYNTHESIS
Synthesis
 Two or more reactants combine to form…
A + B  AB
Synthesis Continued
2 Mg
+
O2  2 MgO
Two reactants form one product
BUT WAIT!!
Don’t forget about everything you have already
learned! Is your equation balanced??
Predicting products
Before we keep going… lets learn a few things about
predicting products
Predicting products
 Here are a few important things to remember
when predicting products:
 The compounds form must be neutral ionic
compounds (which means you’ll be paying
attention to their charges)
 You do NOT carry subscripts from the reactants to
the products.
 You always balance your equation LAST
Let’s go back to that
synthesis example
 Remember the reaction:
Mg
+
O2 
Helpful hint for later…why is
oxygen O2 and not just O?
Click to find
out why
Why O2??
Oxygen is a diatomic molecule, which
means when oxygen is by itself it must
be O2. Remember that this DOES NOT
mean that oxygen is O2 in compounds,
only by itself!
 What are the other diatomic elements? (hint:
remember the heavenly 7!
Go back
Now to predict the products…
Mg
+
O2 
 Remember A + B  AB so Mg + O2
will make a compound with
magnesium and oxygen. What does a
compound with magnesium and
oxygen look like??
A compound with magnesium
and oxygen…
Magnesium is a metal, oxygen is a nonmetal so
we must be forming an IONIC compound.
What’s the charge of Mg?
Mg
2+
What’s the charge of O?
O
2-
So what’s the compound?
Pick…
2+
Mg
MgO2
2O
MgO
Mg2O2
Nope!
MgO2
+2
+
2(-2)
DOES NOT EQUAL ZERO
Try again!
Nope!
Mg2O2
2(+2)
+
2(-2)
=0
But remember ionic compounds need
to be in the simplest form
Try again!
Yes!
Very good!
 MgO is a neutral, correct ionic compound so
our formula is
Mg + O2  MgO
Finally, balance the equation to satisfy the law
of conservation of mass…
2Mg + O2  2MgO
So remember…
 When predicting products:
 Make correct ionic compounds
 THEN balance
Let’s move on to the rest of the reaction types…
Decomposition
Decomposition
forms two or more products
AB  A + B
Decomposition Continued
The electrolysis of water is when water
decomposes into hydrogen and oxygen gas
as shown below:
2H2O  2H2 + O2
Predicting products and
decomposition
 Lets use that same reaction. What if we were
not already given the products, how would
we predict them?
H2O  ??
Water is made of hydrogen and
oxygen, so will my products just
be H and O?
No!
 Remember, H and O are both diatomic
elements.
H2O  H2 + O2
But wait….something is
still missing….
Balance!
 Don’t forget to balance your equation after
you make your products! Your final answer
should look like this:
2H2O  2H2 + O2
You try one…
 What is the correct reaction for the
decomposition of sodium chloride, NaCl?
NaCl  Na + Cl
2NaCl  Na2 + Cl2
2NaCl  2Na + Cl2
Nope!
NaCl  Na + Cl
 Don’t forget that chlorine is a diatomic
element, so it must be Cl2
Try again!
Nope!
2NaCl  Na2 + Cl2
 Although this reaction is correctly balanced,
sodium is NOT a diatomic element
Try again!
Yes!
Very good!
2NaCl  2Na + Cl2
 This is a correct reaction for the
decomposition of sodium chloride.
Ready for the last type of reaction?
Combustion
Combustion
 Combustion is the burning of hydrocarbons.
Hydrocarbon?? What’s that?? Click
to find out!
 When a hydrocarbon reacts with oxygen (O2),
the products are ALWAYS…..
Yes,
ALWAYS…
Carbon dioxide and water
CO2
+ H 2O
Hydrocarbons
 A hydrocarbon is an organic molecule made
up of hydrogen and carbon. Remember when
we learned about these when we talked
about organic chemistry??
C20H42
CH4
C6H10
Combustion Cont…
 Since the products of a combustion reaction
are always CO2 and H2O, the hardest part
about combustion reactions is balancing
them
CH4 + O2  CO2 + H2O
Balance this equation…
Combustion Cont.
CH4 + O2  CO2 + 2H2O
 Be aware… this reaction was pretty easy to
balance, some of the combustion reactions
get pretty complicated! Like this one…
4C3H9 + 21O2  12CO2 + 18H2O
Ready for your quiz??
Yes!
Not quite, review the types of
reactions with me…
Review
 Synthesis reactions: two or more reactants
combine to form ONE product
A + B  AB
 Decomposition reactions: ONE reactant
breaks down into two or more products
AB  A + B
 Combustion reactions: a hydrocarbon reacts
with oxygen to produce carbon dioxide and
water.
Hydrocarbon + O2  CO2 + H2O
Ok, now I’m ready for the quiz!
Quiz Question 1/5
 Which of the following is a decomposition
reaction?
2Fe + O2  2FeO
Na + AgCl  Ag + NaCl
Na2S  2Na + S
Nope!
2Fe + O2  2FeO
 This is two reactants forming ONE product
which is an example of a synthesis reaction
Try
again!
Nope!
Na + AgCl  Ag + NaCl
 This reaction does not just form one product.
This reaction is an example of a single
replacement reaction which we will learn
about later.
Try
again!
Yes!
Very good!
Na2S  2Na + S
 This reaction is ONE reactant breaking down
into two or more products, which is an
example of a decomposition reaction.
Back to the
question!
Next
question!
Quiz Question 2/5
 How can you recognize a combustion
reaction?
A combustion reaction
is the only reaction
always has at least
two reactants and two
products. One of the
reactants is always
oxygen gas.
A combustion reaction
always has a
hydrocarbon reacting
with oxygen to
produce carbon
dioxide and water.
A combustion reaction
always has a
hydrocarbon reacting
with nitrogen, which is
a very explosive
reaction.
Nope!
A combustion reaction
is the only reaction
always has at least
two reactants and two
products. One of the
reactants is always
oxygen gas.
 We will learn about other reactions that can
have more than one product and more than
one reactant. This is NOT the way to identify
a combustion reaction.
Try again!
Nope!
A combustion reaction
always has a
hydrocarbon reacting
with nitrogen, which is
a very explosive
reaction.
 Although combustion reactions are typically
explosive, it is not because they react with
nitrogen.
Try again!
Yes!
Very good!
A combustion reaction
always has a
hydrocarbon reacting
with oxygen to
produce carbon
dioxide and water.
 This is how we identify a combustion reaction
Back to
the
question!
Next
question!
Quiz Question 3/5
 Pick correct bubble that finishes the reaction
below.
K + Cl2  ??
K + Cl2  KCl
2K + Cl2  2KCl
K + Cl2  KCl2
Nope!
K + Cl2  KCl2
 Remember to not carry subscripts over to
your products. K has a +1 charge and Cl has a
-1 charge so the product of KCl2 is not neutral
and cannot be correct.
Try
again!
Almost!
But not quite…
K + Cl2  KCl
 Although this product is correct, the equation
is not balanced!
Try
again!
Yes!
Very good!
2K + Cl2  2KCl
 The products are correct and the reaction is
balanced! Great job!
Back to
the
question!
Next
question!
Quiz Question 4/5
 Pick correct rectangle that finishes the
reaction below.
C2H8 + O2  ??
C2H8 + O2 CO2 + H2O
C2H8 + O2 C2H8O2
C2H8 + 4O2 2CO2 + 4H2O
Almost, but not quite…
C2H8 + O2 CO2 + H2O
 Great job predicting the products, but….
don’t forget to balance!!
Try again!
Nope!
C2H8 + O2 C2H8O2
 Remember that combustion reactions always
have carbon dioxide and water as products
Try again!
Yes!
Very good!
C2H8 + 4O2 2CO2 + 4H2O
 Products are correct and the equation is
correctly balanced. Great job!
Back to the
question!
Next
question!
Quiz Question 5/5
 Pick correct rectangle that finishes the
reaction below.
Al + N2  ??
Al + N2  AlN2
3Al + N2  Al3N2
2Al + N2  2AlN
Nope!
Al + N2  AlN2
 Remember we do not carry over subscripts.
Aluminum has a +3 charge and nitrogen has a
-3 charge so a formula of AlN2 is not a neutral
compound
Try again!
Nope!
3Al + N2  Al3N2
 Although this equation is balanced, since
aluminum has a +3 charge and nitrogen has a
-3 charge, this is not a neutral compound
Try again!
Yes!
Very good!
2Al + N2  2AlN
 A correct neutral compound for the product
and a balanced equation. Great!
Back to the
question!
Finish!
Congratulations!
You have finished the chemical reactions tutorial
Go back
to the
start

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