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Chemical Reaction Notes

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Name
ChemistryoPreAP
Period
NoLes: ChemHeaM Reactions
Review: Some elements do not occur as single atoms when uncombined with other elements.
They will bond with themselves, forming a .ÿÿvli (
molecule. In any chemical
reaction, when you see these elements alone, they musZ be shown with a diatomic formula:
DHat:omU€ @Metlÿ@ÿt$ÿ N2f ÿ2v 02g F2r CU2z Br2u I2
"! Bring Clay For Our New Hut" OP, "Hÿr'ÿFÿ'''ÿ''
UDI FIIÿII,ÿI
And even though these are elements, the correct term for their particles is molecule, not atom.
lo Deserib#lÿmicaÿ Cÿ
Ao WrHtia# Equations
Words can be used to describe
_ÿ_ÿÿqÿ , but that can become
long and awkward, not to mention less useful.
,
Chemists use ÿ ÿ to describe reactions. In chemical
equations,
. and ÿ are used to represent the
reaction.
Symbols Used in Chemical Equations:
Symbol
Meaning
combine with, reacts with
yields, forms j ÿoauces
reversible reaction
solid
liquid
gas
dissolved in water, aqueous solution
heat is supplied to the reaction
cs) oÿ (4/)
"
(a) ÿ,ÿ Ct) "
precipitate is formed (2 possibilities)
gas is released (2 possibilities)
catalyst
Ex 1: Solid iron reacts with oxygen gas to produce iron (III) oxide (rust).
q Feÿs) + 30:ÿ ÿ1 Fez oÿ ÿs)
Ex 2: Solid sodium bicarbonate reacts with hydrochloric acid to produce aqueous sodium chloride,
water, and carbon dioxide gas.
Practice
l. Write equations for each chemica! reaction:
a. Solid sulfur burns in oxygen gas to form sulfur dioxide gas.
b. Heating potassium chlorate solid in the p_esencer ' of the
catalyst manganese(IV)oxide produces oxygen gas. Potassium
chloride is left as a solid.
2° Write a sentence that describes each chemical reaction,
a.ÿ KOH(aq) +,H2SO4(aq) ÿ H20(1) + K2SO4(aq)
b, Na(s) + H20(1) -ÿ NaOH(aq) + H2(g)
B, Balancing Chemical Equa%ions
® In order to correctly ÿ
chemical equations, always remember the law of
F
conservation of jqÿL¢ÿ.ÿ . (In any chemical reaction, fl4ÿ cannot be
or_ a
® An equation that gives the same ÿ
.)
. of each type of ÿ__ on the
left and right sides of the equation is called a ÿJaÿ.6ÿ ____. equation.
Numbers called ÿ__¢_b4ÿ:id4ÿ__ÿ
_ are placed in front of the ÿ:ÿ. When
no coefficient is written, it is assumed to be I
, The (Zÿ-ÿ-3Yÿ{ÿ..ÿ
_zÿ¢ÿuuLÿ
tells you the number of ÿ'ÿs , ÿ
., or
__ ÿ: _ of that element/molecular compound/ionic compound
used or produced in the reaction.
The coefficient also tells you the number of*ÿ ÿ £ÿ *ÿ* of the element or
compound used/produced in the reaction.
Interpreting a balanced equation in two ways:
Ex 1: 4 Fe(s) + 3 02(g) ÿ 2 Fe203(s)
Ex 2: C(s) + 02 (o) ÿ C02(g)
2
I Tips for Balancing Chemical Reactions
Determine the correct formulas for all the reactants and
products.
Write formulas for reactants on left and formulas for
products on right with ÿ in between. Separate multiple
reactants and products with a + sign.
Count the number of at om__ss of each element in the reactants
and products.
Balance the elements one at a time by using coefficients.
-
it's easier to begin with elements that appear only once.
- neve____ÿr balance by changing subscripts within a formula.
Once you determine correct formulas, they should never be
changed°
many times you can treat polyatomics as one unit (if they
appear on both sides of the equation)
Check the numbers of each atom or polyatomic ion to be sure
the equation is balanced
Finally, make sure all the coefficients are in the lowest
possible whole number ratio. Reduce if necessary. ALL
coefficients must reduce if you do this!
Ex 1' Write a balanced equation for the reaction of copper metal and an aqueous solution of
silver nitrate to form aqueous copper (II) nitrate and silver.
Ex 2: Balance the following reaction:
Practleeÿ
Write balanced chemical equations:
i. Potassium metal and water form aqueous potassium hydroxide and
hydrogen gas.
2_ K (s) + 2 M zO( ) --> 2 K 0 +
2. Aqueous calcium hydroxide and sulfuric acid react to form
aqueous calcium sulfate and water.
3. Balance the following equations.
a.
ÿ so2 + o2 ÿm 9_,so3
b. __Fe203 + Jÿ H2 ÿ ÿ Fe +
c. _ÿp +
5oÿ ÿ
PÿOl0
d. ÿ=ÿ_AI + N2 ÿ
ÿA!N
e. ÿ___ÿ_C2H6 + __7__ 02 ÿ
f. C3H8
+ 5
02
Hÿ.O
ÿ
q C02 + _..ÿ H20
3 CO2
+
ÿ___H20
3
Ilo T es of {:;heroical Reactions
Ao Classifying Chemical React[ens There are 5 basic types of chemical reactions:
1. ÿ +r1£1ÿ S
' two or more substances combine to create a more complex substance
Genera! Form' A + )( --9 AX
(b)
: a complex substance is broken down into two or more simpler
substances
General Form: AX-ÿ A + X
Ex: 2 ffÿCl{S} ÿ 2KCs} 4ÿ Cl= c9)
: one element takes the place of another in a
compouild
(meÿfÿ, I ")
General Form: AXiÿDÿ DX ÿFA
OR AX'+Z -=ÿ ,/ÿZ 4- X
Ex:
2ÿo, P{ÿ) ÿ Cla.t,
' ions from two ionic compounds switch places
General Form: /ÿX-+ b'Z =ÿ
Ex: Li Qÿ}4. AgN0sÿ} -ÿ Li140ÿ4} + AgClÿ)
Co)
5. _Cÿ:ÿts'h,o'ÿq
: a substance combines with oxygen and burns, releasing a large
amount of energy in the form of light and/or heat
General Form: (hydrocarbon combustion) ÿ×ÿ/+ Om{_9ÿ ÿ-9 C_OÿrÿBÿ +
Practice:
Balance and identify type.
bZ
a. Pb(NO3) 2 + __K2CrO4 ÿ PbCrO4 + 22ÿ KNO3
C
b.
2 C3Hÿ + ÿ__O2 ÿ
ÿ CO2
$
C. ÿL__Li + 02 ÿ
D
d. MgC03 ÿ MgO +
sR.
+ iH20
ÿ Li20
C02 Otlr'ÿ bÿÿ(ÿl,
e. __ C12 +ÿJ- KI ÿ ÿ-KCI +
T2
ca t%e
4
B° Predicting Products of Chemican Reactions
I. General Guidelines
To predict the products of a chemical reaction, you must first recognize the ÿIAD¢'.
ZTrÿ
reaction:
reactants
element + element
1 compound
of
Iprobable ÿe
C
element + compound(aq)
compound(aq) + compound(aq)
hydrocarbon + oxygen
You then need to be familiar with the mechanism of that particular reaction so you can predict
the product(s),
Ex: copper (I) oxide solid ÿ ÿ eta ÿ po s eÿoÿ Cb)
Type of reaction? Products? Write and balance.
Practice
Classify by reaction type and write a fully balanced equation by predicting products:
5) 1) Sodium metal + chlorine gas -->
2. DJo:cs) 4- Clÿcÿ) ÿ 2_ NÿCI csÿ
) 2) propane (QHs) gas + oxygen gas ->
Uthlurn
Potassium
2. Detailed Instructions: Single Replacement Reactions
One element will replace another element in a compound IF it is more reactive.
Calcium
Otherwiseÿnÿ
Sodium
ÿ=
Magneÿium
Activity Series of Metals
Aluminum
o-in order from most to least active in single replacement reactions
--Hydrogen can also participate in single replacement reactions with metals
Whether one ÿÿ will displace another ÿ from a
compound can be determined by the relative ÿÿ,4ÿ.
of
the two metals,
The _ÿ'6S
Manganese
Zinc
Chronllum
I ton
Cobalt
Nickel
of metals lists metals in order
of_.ÿ_ reactivity. (meaning metals at the bottom are less
reactive than those at the top.)
o In a single-replacement reaction, a metal will 1"6DIz;LCÿ any metal
that is __ÿ0_6ÿ ÿ
Barium
it in the activity series.
Tin
Lead
(l+ÿdrogen)
Copper
Mercury
Silver
Platinum
Gold
Zn(NO3)2(aq)--ÿ ÿcJ([#ÿ]2. # ÿ
Mg(s) +
AgNO3(aq) ÿ ÿ4ÿ(ÿ0Bÿ$ ÿ A9
__ Mg(s) +
Ex 3:
__Mg(s) +
A ÿOflÿJ
can also replace another _oÿÿ__
This is usually limited to
ÿlOQdÿ4,1S__ and they have their own
J
activity series.
The activity of halogens ÿÿ
as you move up
group 17 / 7A. (Fluorine is more active than _Z?,ÿ ÿo rl r! 6
Practice:
a.
c.
d.
.) Halogen Activity Series
Write a balanced equation for each SR reaction°
Zn(s) +
I2(s) +
C12(9) +
<
H2SO4(aq) ÿ ÿ£|S0ÿ t
NaF(aq) ÿ
ÿm
ÿ
2 NaBr(aq) ÿ 2 ÿCI -ÿ ÿt2
3. Detailed Instructions: Double-Replacement Reactions
All double-replacement reactions produce either a ,ÿ;ÿe giOiÿ,___(abbreviated ppt,
an insoluble solid made from 2 solutions), a gas, or water.
To predict products, simply ÿ
the cations (or anions) in each reactant. The
ions "switch partners."
After switching partners, in order to determine if a precipitate forms, consult the solubility
rules: (see next page for chart) - chart will be provided on assessments.
o
k
o
m
Compounds of NNÿ and the alkali metal cations
Compounds of NNÿ and the alkali rnÿal cations
Compounds of NHÿ and the alkali metal cations
Compounds of NNÿ and the alkali rnatal cations
Compounds of NN4+, the alkali metal cations,
G32ÿ, Srÿ, and Baÿ÷
$2-
Compounds of NHÿ, the alkali metal cations,
Caaÿ-, Sra% and Baÿ
Practice: Predict products for the following pairs of aqueous solutions (DR). Determine whether
or not a precipitate will occur by consulting the solubility rules above. If a precipitate forms (and
therefore a reaction occurs), write a balanced equation, INCLUDING ALL STATE SYMBOLS. (aq)
means aqueous/soluble; (s) means solid/insoluble/precipitate. If no reaction occurs, write NR.
Ex 1: Pb(NO3)2(aq) + 2 Kf(aq) ÿ ÿ7ÿbÿ& (S) + ÿ KÿO3(O,_fl)
Ex 2: NaOH(aq) +
Ex. 3:
Sodium chloride and lead (II) nitrate
Ex. 4: Magnesium nitrate and silver acetate
Ex. 5:
Ammonium sulfate and barium chloride
(N'du)z 4:. Ba C! 2
Practice
i. Write balanced equations for these DR reactions.
a.
3 NaOH(aq) + Fe(NO3)B(aq)
b.
3_KOH(aq) +
H3PO4(aq)--°ÿ K[@?Oÿ ((][q] 4-5ÿZ0(ÿ] "ÿ'ÿOÿ
Nora practice
Write a balanced equation for each of these:
Predicting products: mixed practice
(ÿ) 1. potassium (s) + sulfur(s) ->
[D) 2.
silver oxide (s)->
2 A%cs
+9)
(ÿ)3. calcium ch!oride(aq) + lead (II) nitrate(aq) -->
CaClzcÿ4ÿ ÷ Pb(ÿoB]ÿ ÿ Ca(ÿOÿ)acÿ t PbCJÿcs)
methane(g) + oxygen(g) -->
(CH4)
Cÿ4ffcÿ) + 2-0ÿc9ÿ --ÿ (if)z(9 + Z 14ÿOLÿ)
(9ÿ_]5. Chromium(s) + lead (II) nitrate(aq) -->
Use Cr2+
Bevond the Simple Examples: Now that you have the basics down, we will add
some special cases of synthesis and decomposition reactions.
S_ynthesis Reactions
1. metallic oxide + water ---> metallic hydroxide (base)
Ex: copper (II) oxide + water ---> copper (II) hydroxide
Cu 0 (s) + 14zO(ÿ ÿ Cu (oÿ4)z is)
,
nonmetallic oxide + water --ÿ acid
Ex: sulfur dioxide + water ---> sulfurous acid
,
nitrogen gas + hydrogen gas --ÿ ammonia gas (just memorize it)
8
,- |iÿ
Decomposition Reactions (in the presence of heat)
1. metallic hydroxide (base) ÿ metallic oxide + water
Ex: copper (I1) hydroxide __£_+ copper (II) oxide + water
Cu(014)2(s)
HzO
)
2. acid ÿ water + nonmetallic oxide
Ex: sulfuric acid ÿ water + sulfur trioxide
Note_: carbonic and sulfurous acids decompose as they form, without addition of heat:
Carbonic acid--> water + carbon dioxide
[4zd03 + C02. %)
Sulfurous acid --+ water + sulfur dioxide
3. metallic carbonate ÷ carbon dioxide + metallic oxide
Ex: iron (I:f) carbonate __L_> carbon dioxide + iron (II) oxide
A
4. metallic chlorate ÿ metallic chloride + oxygen
Ex: iron (II) chlorate ÿ iron (II) chloride + oxygen
REDOX REACTIONS
Oxidation Number: A number assigned to an element, based on the distribution of
electrons. The same element can have very different properties in different oxidation states.
Rule
:L The oxidation number of any uncombined element is O
Example
Ox. # of Na(ÿ)is
2 The ox. # of a monatomic ion equals the charge of the ionOx. # of Cl-is -- I
3 The more electronegative element in a binary molecular Ox. # of O in NO is
compound is assigned the # equal to the charge it would have
-2if it were an ion
4
5
The ox. # of fluorine in a compound is always -1
OX.
Oxygen has an ox. # of -2 unless it is combined with F (when it
is +2), or it is in a peroxide like H202 (when it is -1)
Ox. # of O in NO2 is -2Ox. # of O in OF2 is + :2.
Ox.
6 The ox. # of H in most compounds is +1 unless it is combined
with a metal, in which case it is -1
Ox.
Ox.
# of Fin LiFis
ÿ1
# of O in Na202 is -I
# of H in H20 is Jÿ I
# of H in LiH is -I
7
In compounds, Group 1 & 2 elements and AI have ox. #s of
+1,+2, +3, respectively
Ox. # of Ca in CaCO3 is
8
The sum of ox. # of all atoms in a neutral compound is 0
Ox. # of C in CaCO3 is ÿ-ÿ[
9
The sum of the ox. # of all atoms in a polyatomic ion equals
Ox. # of P in H2PO4- is
the charge of the ion
+5
*See worksheets for more practice/examples of assigning oxidation numbers.
O×idation is a reaction in which the atoms or ions of an element experience an increase in
oxidation state. An increase in oxidation state means that the oxidation number becomes
more positive. Therefore, the species has lost electrons.
9
0
E×:
+ÿ 12
Na÷ Na+ + e-
Reduction is a reaction in which the oxidation state of an element decreases. A decrease in
oxidation state means that the oxidation number becomes more negative. Therefore, the
species has gained electrons.
0
E×:
--Z
CI2 + 2e-=> 2CI-
Since oxidation is the aosing of electrons and reduction is the #ainhÿg of electrons, they have
to occur simultaneously and the number of electrons produced-in oxidation must equal the
number of electrons acquired in reduction.
**Any chemical process in which elements undergo changes in oxidation number is an
oxidation=reduction reaction, or redo× reaction for short.ÿ
See worksheets for practice in determining which types of reactions are redox and which are
not.
If 2 elements are experiencing a CHANGE in oxidation number from reactants to
products, it's redo×!
Summarizing tip: All of the 5 basic reactionÿ(except for a few exceptions) we have
learned are redox reactions except for one. What is it???
dOÿÿÿ
10
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