Download Chemical Reactions

CHEMICAL REACTIONS
Basics
OBJECTIVES
All
Chemical reactions have a few things in
common
 They
all start with the reactants
 They
all end with the products
 The
total mass at the beginning is equal to the
total mass at the end (law of conservation of
__?____)
If I start with 10g of O at the beginning, then I will
have 10g of O at the end
CHEMICAL REACTIONS
In
English, we use sentences to
explain what is happening
In
chemistry, we use equations to
explain what is happening as well.
This
reads “Reactants yield (or
produce) products.”
Say
that I wanted to say that iron
reacts with oxygen to make rust.
I
could say just that
 But
I could just as easily say
Iron + Oxygen  Iron (III) Oxide
(not balanced)
Oxidation state (charge from valence electrons)

Use a + sign when you have more than one compound
Say
that I wanted to say that hydrogen
peroxide decomposes into water and
oxygen.
I
could say just that
 But
I could just as easily say
Hydrogen Peroxide  water + oxygen
(not balanced)
Say
that I wanted to say that methane
and oxygen combine to form water
and carbon dioxide (word equation)
I
could say just that
 But
I could just as easily say
Methane + oxygen water + carbon
dioxide (not balanced) (Skeleton
Equation)
This a
skeleton equation. It does not balance the equation or tell
us any ratios
Fe+
O2 Fe2O3
H2O2
CH4
 H2O + O2
(g) + O2 (g)  CO2 (g) + H2O (l)
The letters in parentheses tell what state the compound is in at the time.
 (aq) refers to a solution with water as the solvent
OBJECTIVES
Though
we can use skeleton equations
to express what is happening in simpler
terms, chemical equations give us
details that we can use to determine
actual amounts.
4
Fe+ 3 O22 Fe2O3
2
H2O2  2 H2O + O2
CH4
+ 2 O2  CO2 + 2H2O
In
an unbalanced equation, we can see
all the products and reactants.
 But
we do not know how many of each that
we need.
 That
would be like making a cake without
knowing how many eggs, how much sugar,
etc. was needed to make it right.
A
balanced equation tells us exactly what
ratio of ingredients we need in order to
get the cake we want.
1.
2.
3.
1. Fe2O3 + H2  Fe
+ H 2O
Compare the number of each
atom in the reactants to the
2. Fe 21
number of the same atom in the
1. O 31
product
2. H 22
Pick one of the unequal atoms
3.Fe2O3 + H2  2Fe
and multiply the compound by
+ H 2O
a number so that the atoms are
Write the skeleton equation
equal on each side. (This
number is called the coefficient)
4.
Repeat steps 2 and 3 until the
equation is balanced
5.
Done
6.
The balanced equation tells us the
ratio (based upon the coefficients)
for each compound in the
products and reactants.
4. In the example to the right, for every 1 Iron oxide molecule
3 hydrogen molecules are required.
5. This also means 2 molecules of iron and 3 molecules of
water are produced.
1. Fe2O3 + H2  Fe + H2O
2.
Fe 21
1. O 31
2. H 22
3. Fe2O3 + H2  2Fe + H2O
4.
Fe 22
1. O 31
2. H 22
5. Fe2O3 + H2  2Fe + 3H2O
6.
Fe 22
1. O 33
2. H 26
7. Fe2O3 + 3H2  2Fe +
3H2O
8.
Fe 22
1. O 33
2. H 66
What
step in the process of
balancing an equation gives
you the most difficulty?
CLOSURE
OBJECTIVES
A
catalyst is anything that can
accelerate a reaction without
being used up
It is not a product or reactant so it is placed above
the arrow when writing a chemical equation
This would be read as hydrogen peroxide in the
presence of manganese (IV) oxide decomposes into
water and oxygen
CATALYSTS
5 TYPES OF CHEMICAL REACTIONS
Combination
reaction
A
reaction in which 2 simple compounds combine to
make 1 compound
Decomposition
reaction
A
reaction in which 1 (complex) compound is
separated into different components
Single
Replacement reaction
A
reaction in which 2 compounds (1 simple &
complex) react and one component on a compound
is replaced by another
VOCABULARY
Double
Replacement reaction
A
reaction in which 2 (complex) compounds
exchange components with each other
Combustion
A
reaction
reaction in which a compound reacts with oxygen
Activity
Series
A
table which shows the relative reactivity of various
compounds. This helps determine which compounds
would be replaced by another.
VOCABULARY
 Normally
this involves 2 elements combining to make
a compound, but it is possible for two compounds to
combine to make a new compound.
 When
a metal is combined with a non-metal, the result
is an ionic compound (salt).
REACTION TYPE: COMBINATION
• When two non-metals are bonded, there can be
multiple products.
• When a transition metal is combined with another
element, multiple products are possible as well.
REACTION TYPE: COMBINATION
REACTION TYPE: COMBINATION
CHEMISTRY
Today is the last day for food, drinks, or
bathroom passes. Until you can clean up after Agenda –
yourselves so I don’t have to, it will remain this
 Bellringer
way.
 Identifying
5
different
reaction types
 Predicting
products for
the different
reaction types
It can sometimes be difficult to predict the products
of a decomposition reaction, but when there are
only 2 components to a compound, the simpler
parts formed in the decomposition are apparent.
REACTION TYPE: DECOMPOSITION
REACTION TYPE: DECOMPOSITION
In the case of water, many times only one H will be replaced
leaving a hydroxide ion combined with the replacing element
In
a single replacement reaction,
normally an element and a component of
a compound exchange places.
Normally positive replaces positive,
negative will replace negative
REACTION TYPE: SINGLE
REPLACEMENT
 An
activity series  helps us predict when
one metal will replace another.
 The
element farther up the list will replace one
lower on the list.
 Also,
a halogen can replace a different halogen
only if it (the halogen to do the replacing) is
above it (the halogen to be replaced) on the
periodic table
This reaction will happen, while the one below will
not.
REACTION TYPE: SINGLE
REPLACEMENT
REACTION TYPE: SINGLE
REPLACEMENT
Remember, keep it clean or no food, drink, or rr.
Bellringer, tell me what type of reaction is shown in each
problem.Also, take 1 of the ten and work it out completely.
CHEMISTRY
Agenda –
 Bellringer
 Identifying
5 different
reaction
types
 Predicting
products
for the
different
reaction
types
A
double replacement reaction is one in which
two compounds exchange the components with
positive charges.
They
are sometimes called double-displacement
reactions
They
generally takes place in an aqueous solution
They
will also often produce a precipitate (solid),a
gas, or some molecular compound such as water.
REACTION TYPE: DOUBLE
REPLACEMENT
 There
are some generalities that apply to double
displacement reactions. One of the following is usually
true.
1.
One of the products is only slightly soluble (able to be
dissolved) and precipitates
2.
One of the products is a gas.
3.
One of the products is a molecular compound like water.
REACTION TYPE: DOUBLE
REPLACEMENT
REACTION TYPE: DOUBLE
REPLACEMENT
A
combustion reaction is a reaction in which an element or a
compound reacts with oxygen, often producing light and heat

Oxygen is always a reactant.

Often a hydrocarbon (CH or their derivatives) is the other reactant


Methane, propane, butane, etc.
Though other elements will combine with oxygen
 These
reactions can often be classified as some of the other 4
types of reactions.
REACTION TYPE: COMBUSTION
REACTION
REACTION TYPE: COMBUSTION
REACTION
OBJECTIVES
 This
is the way that we have done balanced reactions
so far
 However,
in aqueous solutions (in water) most ionic
compounds dissociate (separate into cations and anions)
 We
can now show a complete ionic equation by
showing each dissolved ionic compounds as being free
ions.
NET IONIC EQUATIONS
 Notice
that the NO3- does not change. Since the nitrate
ion and the sodium ion appear on both sides of the
equation and they do not seem to do anything in this
reaction, they are called a spectator ions. We will
actually not even show them in the reaction.
 This
new equation is called a net ionic equation (net as
in after everything that is not important is removed).
NET IONIC EQUATIONS
 In
the previous reaction, both sides of the equation
are balanced (neutral on both sides)
 In
any net ionic equation the charge on the
reactant side must equal the charge on the product
side.
 In
this reaction, nitrate is the spectator ion again.
NET IONIC EQUATIONS
 In
this net ionic reaction, there is a +1 charge on the
reactant side and a +2 charge on the product side.
This is unacceptable.
NET IONIC EQUATIONS
A
precipitate (ppt) is a solid
that is sometimes formed when
combining two non-solid
reactants.
The
only way to know if it will
form a ppt is to look at its
solubility.
 If
it is insoluble, then it will form a
ppt.
PREDICTING A
PRECIPITATE
For
this we have to look at the
chart to the left.
This should be a double
displacement reaction forming
sodium nitrate (soluble) and
barium carbonate (insoluble)
PREDICTING A
PRECIPITATE
This
leaves us the above reaction
as our net ionic reaction
PREDICTING A
PRECIPITATE
A
precipitate (ppt) is a solid that is
sometimes formed when combining two
non-solid reactants.
 The
only way to know if it will form a ppt is to
look at its solubility.
 If
it is insoluble, then it will form a ppt.
PREDICTING A
PRECIPITATE