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All chemical reactions… have two parts:
1. Reactants = substances you start with
2. Products = end with reactants turn into products Reactants Products
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In a chem rxn Atoms not created or destroyed (Law of
Conservation of Mass) rxn described in a:
#1. sentence every item is a word Copper reacts with chlorine to form copper (II)
chloride.
#2. word equation some symbols used
Copper + chlorine copper (II) chloride
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Symbols in equations? – Text page 323
arrow (→) separates reactants from products (points to products)
–Read as: “reacts to form” or yields plus sign = “and” (s) after formula = solid: Fe(s)
(g) = gas: CO2(g)
(l) = liquid: H2O(l)
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Symbols used in equations(aq) after formula = dissolved in
water, aqueous solution: NaCl(aq) is salt water solution
used after product - indicates gas produced: H2↑
used after product - indicates solid produced: PbI2↓
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Symbols used in equations■ double arrow indicates a
reversible reaction (more later)■ shows that
heat supplied to rxn■ indicates catalyst
supplied (here, platinum is catalyst)
heat ,
Pt
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What is a catalyst? substance that speeds up
rxn, w/o being changed or used up in rxn
Enzymes - biological or protein catalysts in your body
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#3. The Skeleton EquationUses formulas and symbols to
describe rxn
–but doesn’t indicate how many; means they’re NOT balanced
All chem equations are description of rxn
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Write a skeleton equation for:1. Solid iron (III) sulfide reacts with
gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.
2. Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.
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Now, read these equations:
Fe(s) + O2(g) Fe2O3(s)
Cu(s) + AgNO3(aq) Ag(s) + Cu(NO3)2(aq)
NO2(g) N2(g) + O2(g)
Pt
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#4. Balanced Chemical EquationsAtoms can’t be created or destroyed
in an ordinary reaction:
–All atoms we start with we must end up with (balanced!)
balanced equation has same # of each element on both sides of equation
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Rules for balancing:1) Assemble correct formulas for all
reactants and products, using “+” and “→”2) Count # of atoms of each type on both sides3) Balance elements one at a time by adding
coefficients (the numbers in front) where you need more - save balancing the H and O until LAST!
(hint: I prefer to save O until the very last)4) Double-Check make sure balanced
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Never change subscript (only change coefficients)
– changing subscript (formula) describes different chemical
– H2O different than H2O2
Never put coefficient in middle of formula; only in front
2NaCl is okay, but Na2Cl is not.
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Practice Balancing Examples
_AgNO3 + _Cu _Cu(NO3)2 + _Ag
_Mg + _N2 _Mg3N2
_P + _O2 _P4O10
_Na + _H2O _H2 + _NaOH
_CH4 + _O2 _CO2 + _H2O
2 2
3
4 5
2 22
2 2
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Types of Reactions5 major types. predict the products predict whether or not they will happen at allHow? We recognize them by their reactants
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#1 - Combination Reactions Combine = put together 2 substances combine to make one
cmpd (also called “synthesis”) Ca + O2 CaO
SO3 + H2O H2SO4
predict products, especially if reactants are 2 elements
Mg + N2 Mg3N2 (symbols, charges, cross)
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Complete and balance: Ca + Cl2 Fe + O2 (assume iron (II) oxide is the product)
Al + O2 Remember first step…write correct
formulas – you can still change subscripts at this point, but not while balancing!
Then balance by changing just coefficients only
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#1 – Combination ReactionsAdditional Notes:
a) Some nonmetal oxides react with H2O - produces acid:
SO2 + H2O H2SO3
b) Some metallic oxides react with H2O - produces base:
CaO + H2O Ca(OH)2
(how “acid rain” forms)
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#2 - Decomposition Reactionsdecompose = fall apartone reactant breaks apart into 2 or
more elements or cmpdsNaCl Na + Cl2
CaCO3 CaO + CO2
Note: energy (heat, sunlight, electricity, etc.) usually required
electricity
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#2 - Decomposition Reactionspredict products if binary cmpd
(made of 2 elements)
–It breaks apart into the elements:H2OHgO
electricity
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#2 - Decomposition Reactions If cmpd has > 2 elements you must
be given one of products
–other product from the missing pieces
NiCO3 CO2 + ___
H2CO3(aq) CO2 + ___
heat
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#3 - Single Replacement ReactionsOne element replaces another (new
dance partner)
Reactants must be an element & cmpd
Products will be a different element and different cmpd
Na + KCl K + NaCl F2 + LiCl LiF + Cl2
(Cations switched)
(Anions switched)
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#3 Single Replacement Reactions Metals replace other metals (they can
also replace H) K + AlN Zn + HCl Think of water as: HOH
–Metals replace first H, then combines w/ hydroxide (OH).
Na + HOH
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#3 Single Replacement Reactions can even tell whether or not single
replacement rxn will happen:–b/c some chemicals more “active” than
others–More active replaces less active
list – p. 333 - Activity Series of Metals
Higher on list replaces lower
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The “Activity Series” of Metals Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead HydrogenHydrogen Bismuth Copper Mercury Silver Platinum Gold
1) Metals can replace other metals, if they are above metal trying to replace (i.e. Zn will replace Pb)
2) Metals above H can replace H in acids.
3) Metals from Na upward can replace hydrogen in H2O
Higher activity
Lower activity
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The “Activity Series” of Halogens
Fluorine Chlorine Bromine Iodine
Halogens can replace other halogens in compounds, if they are above halogen they are replacing
2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)
MgCl2(s) + Br2(g) ???No Reaction!
???
Higher ActivityHigher Activity
Lower ActivityLower Activity
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#4 - Double Replacement Reactions Two things replace each other.
–Reactants must be two ionic compounds, in aqueous solution
NaOH + FeCl3 –positive ions change place (dance partners)
NaOH + FeCl3 Fe+3 OH- + Na+1 Cl-1
= NaOH + FeCl3 Fe(OH)3 + NaCl
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#4 - Double Replacement Reactions Have certain “driving forces”, or reasons
–only happens if one product:
a) doesn’t dissolve in water & forms solid (a “precipitate”), or
b) is gas that bubbles out, or
c) is molecular compound (usually water)
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Complete and balance:assume all of the following
reactions actually take place:
CaCl2 + NaOH
CuCl2 + K2S
KOH + Fe(NO3)3
(NH4)2SO4 + BaF2
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How to recognize which type?Look at the reactants:
E + E =Combination
C = Decomposition
E + C = Single replacement
C + C = Double replacement
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#5 – Combustion Reactions Combustion means “add oxygen” Normally, a cmpd composed of only
C, H, (and maybe O) is reacted with oxygen – called “burning”
Complete combustion, products are CO2 and H2O
If incomplete, products are CO (or possibly just C) and H2O
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Combustion Reaction Examples:
C4H10 + O2 (assume complete)
C4H10 + O2 (incomplete)
C6H12O6 + O2 (complete)
C8H8 + O2 (incomplete)
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SUMMARY: An equation... Describes a rxn Must be balanced (follows the Law of
Conservation of Mass) only balance by changing coefficients special symbols to indicate physical
state, catalyst or energy required, etc.
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Reactions 5 major types We can tell what type they are by
looking at reactants Single Replacement happens based on
the Activity Series Double Replacement happens if one
product is: 1) a precipitate (an insoluble solid), 2) water (a molecular compound), or 3) a gas
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Section 11.3Section 11.3p. 342p. 342
Reactions in Aqueous SolutionReactions in Aqueous Solution
Co(NOCo(NO33))22
KK22CrCr22OO77 KK22CrOCrO44
NiClNiCl22 CuSOCuSO44
KMnOKMnO44
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Net Ionic EquationsMany reactions occur in water- that
is, in aqueous solutionWhen dissolved in water, many
ionic cmpds “dissociate”, or separate, into cations & anions
Now write ionic equation
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Net Ionic Equations Example (needs to be a double replacement reaction)
AgNO3 + NaCl AgCl + NaNO3
1. this is the full balanced equation
2. next, write it as ionic equation by splitting the cmpds into their ions:
Ag1+ + NO31- + Na1+ + Cl1-
AgCl + Na1+ + NO31-
Note that the AgCl did not ionize, because it is a “precipitate” “precipitate” (Table 11.3 p. 344)(Table 11.3 p. 344)
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Net Ionic Equations3. simplify by crossing out ions not
directly involved (called spectator ions)
Ag1+ + Cl1- AgCl
This is called the net ionic equation
Let’s talk about precipitates before we do some other examples
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Predicting the Precipitate Insoluble salt is a precipitate
[note Figure 11.11, p.342 (AgCl)] General solubility rules are found:
a) Table 11.3, p. 344 in textbook
b) Reference section - page R54 (Table B.9)