Download Chemical Reactions Chapter 11

Chemical Reactions
Chapter 11
SC2 Students will relate how the Law of Conservation of Matter is used
to determine chemical composition in compounds and chemical
reactions.
SC2.a. Identify and balance the following types of chemical equations:
Synthesis, Decomposition, Single Replacement, Double Replacement, and
Combustion
SC2.b. Experimentally determine indicators of a chemical reaction
specifically precipitation, gas evolution, water production, and changes in
energy to the system.
1
Writing chemical Equations
• In chemical reactions one or more reactants
change into one or more products.
• Chemists use a chemical equations to convey a s
much information as possible about what
happens in a chemical reaction.
• The reactants are written on the left and the
products on the right
• An arrow separates them, read the arrow as
yields, gives, or reacts to produce.
Reactants → products
– example: iron + oxygen → iron (III) oxide
2
Writing chemical Equations
• To write word equations, write the names of the
reactants to the left of the arrow separated by plus
signs; write the names of the products to the right of the
arrow, also separated by plus signs.
– Example: hydrogen peroxide decomposes to form water and
oxygen gas
– Hydrogen peroxide → water + oxygen
• Chemical equation is a representation of a chemical
reaction
• Skeleton equation is a chemical equation that does not
indicate the relative amounts of the reactants and
products.
• Write the formulas of the reactants to the left of the
yields sign (arrow) and the formulas of the products to
the right.
3
Writing chemical Equations
• You can indicate the physical states of
substances by putting a symbol after each
formula: (s) = solid, (l) = liquid, (g) = gas, and
(aq) = aqueous solution [a substance dissolved in
water]
• Example: Fe (s) + O2 (g) → Fe2O3 (s)
• Catalyst is a substance that speeds up the
reaction but is not used up in the reaction.
• A catalyst is neither a reactant nor product and
is written above the arrow.
4
5
Types of equations
• Word equation
– Carbon Dioxide + Water  Glucose + Oxygen
• Skeletal equation
– CO2 + H2O  C6H12O6 + O2
• Skeletal equation with phases
– CO2 (g) + H2O (l)  C6H12O6 (s) + O2 (g)
• Balanced equation
– 6CO2 + 6H2O  C6H12O6 + 6O2
6
Types of Reactions
1. Combination (synthesis) reaction is a chemical
change in which two or more substance react for
form a SINGLE NEW SUBSTANCE.
– Example: 2H2 + O2 → 2H2O
– Combination reactions are easy to recognize because they
have two reactants and one product.
2. Decomposition reaction is a chemical change in
which ONE SUBSTANCE reacts to form TWO or more
new substance.
– Example: 2H2O → 2H2 + O2
– Decomposition reactions are easy to recognize because
they have one reactants and two or more products.
7
Types of Reactions
3. Single replacement reaction is a chemical change in which
ONE ELEMENT replaces another element in a
COMPOUND.
– you can recognize a single replacement reaction because both
the reactant and the product have an element and a
compound
– example: 2K + 2H2O → 2KOH + H2
4. Double-replacement reaction is a chemical change
involving an exchange of positive ions between two
compounds.
– you can recognize a double-replacement reaction because
both the reactants and the products are two compounds
– They generally take place in aqueous solutions, and often
produce a precipitate, a gas, or a molecular compound such as
water.
– FeCl3 + NaOH → Fe(OH)3 + NaCl
8
Types of Reactions
5. Neutralization Reaction is a special type of doublereplacement reaction. It is a chemical change where
an acid and a base react to form water and a “salt”
– Most bases are hydroxides, example: sodium hydroxide
{NaOH}
– Most acids start with hydrogen, example: hydrochloric
acid {HCl}, sulfuric acid {H2SO4}
– Salts are defined as ionic compounds
– Example: NaOH + HCl → H20 + NaCl
6. Combustion reaction is a chemical change in which
an element or a compound reacts with oxygen often
producing energy in the form of heat and light.
– Often the other reactant is a hydrocarbon or an alcohol
and the products are carbon dioxide and water.
– Example: CH4 + O2 → CO2 + H2O
9
Types of Reactions Summary
Type of Reactants
Reaction Type
Products
2 elements ONLY
Combination or
synthesis
Compound
1 compound ONLY
Decomposition
Elements
C, H, O and O2 ONLY Combustion
CO2 + H2O
ALWAYS
1 element and 1
compound
Single replacement
1 compound and 1
element
2 compound
Double Replacement
2 compounds
Acid + Base
Neutralization
H2O + “salt”
10
Types of Reactions Practice
a. Al + CH3OH  (CH3O)3Al + H2
a. Single Replacement
b. Ba(NO3)2 + CuSO4  BaSO4 + Cu(NO3)2
b. Double Replacement
c. N2 + H2  NH3
c. Combination
d. H2O (l) + SO3 (s)  H2SO4 (aq)
d. Combination
e. KOH + H3PO4  K3PO4 + H2O
e. Neutralization
f.
C4H10 + O2  CO2 + H2O
f.
Combustion
g. H2O2  H2O + O2
g. Decomposition
h. KI + Cl2  KCl + I2
h. Single Replacement
i.
AgNO3 + KCl  AgCl(s) + KNO3
i.
Double replacement
j.
NaHCO3(s)  Na2CO3(s) + H2O(l) + CO2(g)
j.
Decomposition
11
Balancing chemical Reaction
• The law of conservation of mass states that
matter is not created or destroyed it merely
changes forms.
• In order to show that mass is conserved the
amount of products and reactants MUST equal.
• Once a word equation is turned into chemical
formulas it must be balanced.
12
Balancing Chemical Equations
• Coefficients are small whole numbers that are placed
in front of the formulas in an equation in order to
balance it.
• Balanced equation is a chemical equation in which
each side of the reaction has the same number of
atoms of each element and mass is conserved.
• To write a balanced chemical equation, first write
the skeleton equation. Then use coefficients to
balance the equation so that it obeys the law of
conservation of mass.
– In every balanced chemical equation each side of the
equation has the same number of atoms of each element.
13
Steps to balancing chemical equations
1. Create a T-chart and List the elements in the
chemical formulas on each side in the SAME order
2. Count the number of atoms of each element on
each side
3. See what elements don’t match in your T-chart
4. Add coefficients in front of one substance at a time,
•
•
Start by balancing the most complex compound first,
general rule of thumb is to save Hydrogen and Oxygen
until the end to balance.
5. recount number of atoms of each element
6. Repeat 3, 4 & 5 until all elements are balanced.
14
Counting Atoms
• In order to balance chemical reactions you MUST
first know how to count atoms.
• Subscripts multiply what ever they are beside
• If a subscript is beside parentheses it multiplies
everything in the parentheses.
• Coefficients multiply everything immediately
behind them.
15
Counting Atoms Practice
•
•
•
•
•
•
•
•
•
H2O
CuSO4
NaHCO3
Cu(NO3)2
(NH4)3PO4
2 H2O
3CuSO4
2 Cu(NO3)2
3 (NH4)3PO4
•
•
•
•
•
•
•
•
•
2 H, 1 O
1 Cu ,1 S,4 O
1 Na, 1 H, 1 C, 3 O
1 Cu,2 N,6 O
3 N, 12 H, 1 P, 4 O
4 H, 2 O
3 Cu, 3 S, 12 O
2 Cu, 4 N, 12 O
9 N, 36 H, 3 P, 12 O
16
Balancing Chemical Reactions Practice
Example 1:
N2 +3 H2  2 NH3
N == 22
| N == 12
H == 62
| H == 36
– Pick an element to start balancing with, I pick N
• Least common multiple between 1 and 2 is 2
– Add 2 in front of product side and recount
– N is balanced so now look at H
• Least common multiple between 2 and 6 is 6
– Add 3 in front of reactant H and recount
– Now both sides are equal so it is a balanced equation
17
Balancing Chemical Reactions Practice
• Is a trial and error process
Example 1: 2NaHCO3  Na2CO3+ H2O + CO2
Na
|
Na
Na = 1
|
Na
=2
2
H= 2
H=1
|| H
2H
C=1
|| CC = 1+1 =2
2C
O=3
|| O
6O
O= 3 + 1 + 2 = 6
• Count Atoms of each element
• Start balancing the most complex item (reactant)
18
Balancing Chemical Reactions Practice
• Is a trial and error process
Example 1: 2 C4H10 +13 O2  48 CO2+ 10
5 H2O
C
CCCC====
4|8484 C | |||CCCC====18484
HH
10
H
|20
H | |||HH
H
H====
10
20
10
H
H====220
220
10
OO
2|26
216
===39==
O
O
O====
222O | |||OO
O
O====
816
8+1
+1
+5
+10
+10
1326
26
• Start balancing the most complex item (reactant)
• Leave H and O until the end
– Have to use whole number and currently have no whole
number… trick: Double all current coefficients and recount.
It is Now Balanced
19
Balancing Reaction Practice – Polyatomic
• Balancing reactions with polyatomics can be a bit complicated
but if the polyatomic is the same on BOTH sides of reaction you
can treat it like a special element.
2 FeBr3 + 3 Ba(OH)2 → 3 BaBr2 + 2 Fe(OH)3
Fe
Fe
11122
| |Fe
Fe
|Fe
Fe 11122
Br
Br
33366
| |Br
Br
|Br
Br 22266
Ba
Ba
| |Ba
Ba 1113
|Ba
Ba 111 33
(OH)
(OH)
| |(OH)
(OH) 222 6
|(OH)
(OH)333 66
• When counting Atoms put a box around JUST the polyatomic
• Count like normal and balance using these count
• Br is 1st thing that don’t balance, common multiple between 2
and 3 is 6
20
Balancing Reaction Practice – Polyatomic
Na33PO
PO44++ 3 MgSO
MgSO44→
→
2 Na
•
•
•
•
•
Mg33(PO
(PO44))22++ 3 Na
Na22SO
SO44
Mg
Na
3333 666
|| ||Na
Na
Na
Na
Na
Na
Na 2222 66
PO
1 22
|| |PO
2
PO
PO
PO
PO4444 11
1 2
|PO
PO4444 22
2
Mg
|| ||Mg
Mg
Mg
Mg
Mg
Mg 1111 3
Mg 3333
SO
|| ||SO
SO
SO
SO
SO
SO4444 1111 3
SO4444 1111 33
When counting Atoms put a box around JUST the polyatomic
Count like normal and balance using these count
Na is 1st thing that don’t balance, common multiple between 2
and 3 is 6.
Fix each side and recount
Mg is next thing that don’t balance, common multiple between
1 and 3 is 3.
21
Predicting Products
• Predicting the products of a chemical reaction
involve 1st determining the type of reaction that
is occurring.
– Combination: starts with 2 elements
– Decomposition: starts with 1 compound
– Single Replacement: Starts with 1 element & 1
compound
– Double Replacement: starts with 2 compounds
– Neutralization: starts with 2 compounds that are an
ACID and a BASE
– Combustion: starts with O2 and a compound
containing C, H and/or O.
22
Predicting Products identifying types
of reaction practice.
____Al + ____Cl2 
Combination
___Mg(OH)2 + ___HCl
Neutralization
___Zn + ____HCl
Single replacement
___C2H6 + ___O2
Combustion
___Al2O3 
Decomposition
__Ba(NO3)2 + __Na2SO4 
Double replacement
23
Predicting Products
• Predicting the products of a chemical reaction
involve next determine the products that would
be produced based on a balance of charge.
– Combination: ends with 1 compound
– Decomposition: ends with 2 elements
– Single Replacement: ends with 1 element & 1
compound
– Double Replacement: ends with 2 compounds
– Neutralization: ends with H2O and a “salt”
– Combustion: ends with CO2 and H2O
24

Predicting Products
____Al + ____Cl2 
Is a combination reaction so the product is a compound between
aluminum and chlorine. MUST BALANCE CHARGES!
Al+3 and Cl-1 form compound
AlCl3
____Al + ____Cl2  ____ AlCl3 still needs number of atoms
to be balanced
___Mg(OH)2 + ___ HCl
Is a neutralization reaction so the product is water and a salt. The
salt would be formed between the element at the beginning of the
base and the element at the end of the acid. Think square
dance!! MUST BALANCE CHARGES!
Mg +2 and Cl-1 form compound
MgCl2 and H2O
___Mg(OH)2 + ___HCl  __ MgCl2 + __ H2O still needs number
of atoms to be balanced
Predicting Products

__Al2O3 
 Is a decomposition reaction so the product is just
elements.
 Don’t forget diatomic elements.
 Al and O2 (is a diatomic element)
 __Al2O3  __ Al + ___ O2
 __Ba(NO3)2 + __Na2SO4 
Is a double replacement reaction, the positive ions
switch partners. MUST BALANCE CHARGES!
__Ba(NO3)2 + __Na2SO4  __BaSO4 + __NaNO3
still needs to be balanced
26
Predicting Products

___Zn + ____HCl
 Is a single replacement reaction so the element
replaces an element in the compound
 Generally the 1st element in compound is the one
that leaves. MUST BALANCE CHARGES!
 ___Zn + ____ HCl ___ZnCl2 + ___H2
 ___C2H6 + ___O2
Is a combustion reaction, and can only make carbon
dioxide and water.
___C2H6 + ___O2 ___ CO2 + _____H2O
27
Predicting Products Summary
Make sure to BALANCE charges for ALL ionic and acid
compounds
Transition Metals use the reactant to determine the
charge and assume that it stays the same.
Once you BALANCE CHARGES do NOT change the
subscripts.
Don’t forget your 7 diatomic elements:
When they are not in compounds they are in pairs
N2, O2, F2, Cl2, Br2, I2, H2
ALL other elements are single elements when not in compounds
Just because an element has a subscript on the
reactant side, does NOT mean it will have the same
subscript on the product side.
28
Word Equations
• When balancing reactions that are word
equations you MUST first write BALANCED
chemical formulas.
• Remember to check the ions that each forms for
Ionic compounds and Acids
• Once you have a balanced chemical formula DO
NOT change the formula (i.e. change subscripts)
• DON’T forget your 7 diatomic elements.
29
Word Equations
• Example 1: solid calcium hydroxide reacts with sulfuric acid
to produce aqueous calcium sulfate and water.
• Pick out the chemical names in the reaction and turn them
into chemical formulas
calcium hydroxide + sulfuric acid → calcium sulfate + water
• calcium hydroxide = Ca+2 OH-1,
– Ca(OH)2
• Sulfuric acid = oxy acid,
– Sulfuric was sulfate, H+1 SO4-2,
– H2SO4
• Calcium Sulfate = Ca +2 SO4-2
– CaSO4
• Water = H2O
• Skeleton Equation becomes:
Ca(OH)2(s) + H2SO4(l) → CaSO4(aq) + H2O (l)
30
Word Equations
• Balancing Example 1
Ca(OH)2(s) + H2SO4(l) → CaSO4(aq) + H2O (l)
Remember polyatomic rule only applies if it is the SAME on
both sides.
Ca(OH)
Ca(OH)2(s)
H22SO
SO4(l)
→CaSO
CaSO4(aq)
H2HO2O
2(s)++H
4(l) →
4(aq) ++ 2
(l) (l)
Ca
Ca 1
1
H
H 4
4
O
O 2
2
SO
SO44 1
1
|| Ca
Ca
|| H
H
|| O
O
|| SO
SO44
11
22 4
11 2
11
31
Word Equations
• Example 2: Aluminum bromide and chlorine gas
react to form aluminum chloride and bromine
gas.
• Don’t forget to balance charges and your 7
diatomic elements
2AlBr
AlBr
ClCl →→ AlCl
AlCl
Br
3 2Br
AlCl
+2 3Br
2 AlBr
2+AlCl
Br2 2
3 3++AlBr
3 3+
2→
3 +2 233+Cl2Cl→
33 +
Al1Al
1 21 Atoms
1Al
1 normal
2 | |AlAl
|like
1 2
NowAl
Balance
BrBr3Br
3 63 6| |BrBr
2 62 6
| 2Br
ClCl2Cl
2 2 6 | |ClCl
3 3 6
| 3Cl
32