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Honors Chemistry
All chemical reactions have two parts:
Reactants - the substances you start with
Products- the substances you end up with
The reactants turn into the products.
Reactants Products
In a chemical reaction The way atoms are joined is changed Atoms aren’t created of destroyed. Can be described several ways:1. In a sentence
Copper reacts with chlorine to form copper (II) chloride.
2. In a word equationCopper + chlorine copper (II) chloride
Symbols in equations the arrow separates the
reactants from the products Read “reacts to form” The plus sign = “and” (s) after the formula = solid (g) after the formula = gas (l) after the formula = liquid
Symbols used in equations (aq) after the formula -
dissolved in water, an aqueous solution.
used after a product indicates a gas (same as (g))
used after a product indicates a solid (same as (s))
Symbols used in equations indicates a reversible
reaction
shows that heat is supplied to the reaction
is used to indicate a catalyst is supplied, in this case, platinum.
heat ,
Pt
What is a catalyst?
A substance that speeds up a reaction, without being changed or used up by the reaction.
Enzymes are biological or protein catalysts.
Skeleton Equation
Uses formulas and symbols to describe a reaction
doesn’t indicate how many. All chemical equations are
sentences that describe reactions.
Convert these to equations Solid iron (III) sulfide reacts with
gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.
Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.
Now, read these:
Fe(s) + O2(g) Fe2O3(s)
Cu(s) + AgNO3(aq)
Ag(s) + Cu(NO3)2(aq)
NO2 (g) N2(g) + O2(g)
Pt
Balanced Equation
Atoms can’t be created or destroyed
All the atoms we start with we must end up with
A balanced equation has the same number of each element on both sides of the equation.
Rules for balancing:
Assemble, write the correct formulas for all the reactants and products
Count the number of atoms of each type appearing on both sides
Balance the elements one at a time by adding coefficients (the numbers in front) - save H and O until LAST!
Check to make sure it is balanced.
Never change a subscript to balance an equation. If you change the formula you are describing a
different reaction.
H2O is a different compound than H2O2
Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not.
Example
H2 + H2OO2
Need twice as much O in the product
R PH
O
2
2
2
1
Example
H2 + H2OO2
Changes the O
R PH
O
2
2
2
1
2
Example
H2 + H2OO2
Also changes the H
R PH
O
2
2
2
1
2
2
Example
H2 + H2OO2
Need twice as much H in the reactant
R PH
O
2
2
2
1
2
2
4
Example
H2 + H2OO2
Recount
R PH
O
2
2
2
1
2
2
4
2
Example
H2 + H2OO2
The equation is balanced, has the same number of each kind of atom on both sides
R PH
O
2
2
2
1
2
2
4
2
4
Example
H2 + H2OO2
This is the answer
R PH
O
2
2
2
1
2
2
4
2
4
Not this
Balancing Examples
_AgNO3 + _Cu _Cu(NO3)2 + _Ag
_Mg + _N2 _Mg3N2
_P + _O2 _P4O10
_Na + _H2O _H2 + _NaOH
_CH4 + _O2 _CO2 + _H2O
Balancing Examples
2AgNO3 + Cu Cu(NO3)2 + 2Ag
3Mg +N2 Mg3N2
4P + 5O2 P4O10
2Na + 2H2O H2 + 2NaOH
CH4 + 2O2 CO2 + 2H2O
Types of Reactions
There are millions of reactions. Can’t remember them all Fall into several categories. We will learn 5 major types. Will be able to predict the products. For some, we will be able to predict
whether they will happen at all. Will recognize them by the reactants
COMBINATION REACTIONCOMBINATION REACTION
A reaction in which two or more substances combine to form a single product.
A +B + CA +B + C ABC ABCCaO(s) + SOCaO(s) + SO22(g) (g) CaSO CaSO33(s)(s)
Write and balance
Ca + Cl2 Fe + O2 Al + O2 Remember that the first step
is to write the correct formulas Then balance by using
coefficients only
DECOMPOSITION REACTIONDECOMPOSITION REACTIONA reaction in which a single compound
reacts to give two or more substances, usually requiring a raise in temperature.
ABCABC A + B + C A + B + C
2KClO2KClO33(s) (s) 2KCl(s) + 3O 2KCl(s) + 3O22(g)(g)
#2 - Decomposition Reactions decompose = fall apart one reactant falls apart into two
or more elements or compounds.
NaCl Na + Cl2
CaCO3 CaO + CO2
Note that energy is usually required to decompose
electricity
#2 - Decomposition Reactions Can predict the products if it is
a binary compound Made up of only two elements Falls apart into its elements H2O HgO
electricity
Fig. 8-13, p. 215
2H2O(l) →
•Can predict the products if it is a binary compound •Made up of only two elements•Falls apart into its elements
#2 - Decomposition Reactions If the compound has more
than two elements you must be familiar with page 10 of your packet
NiCO3
KClO3(aq)
pp. 218, 220
Single Displacement (or Replacement) Reactions
Fig. 8-15, p. 218
Single Displacement (or Replacement) Reactions
PREDICT THE PRODUCT
1. Ca + HCl
2. ZnBr2 + I2
3. Cu + AgNO3
Answers are on the next slide.
#3 Single Replacement Metals replace other metals (and
hydrogen) K + AlN Zn + HCl Think of water as HOH Metals replace one of the H,
combine with hydroxide. Na + HOH
We can tell whether a reaction will happen
Some chemicals are more “active” than others
More active replaces less active
There is a list on page 11 - called the Activity Series of Metals
Higher on the list replaces lower.
#3 Single Replacement Note the * concerning Hydrogen H can be replaced in acids by everything
higher Li, K, Ba, Ca, & Na replace H from acids
and water Fe + CuSO4
Pb + KCl Al + HCl
#3 - Single Replacement What does it mean that Hg and Ag are
on the bottom of the list? Nonmetals can replace other
nonmetals Limited to F2 , Cl2 , Br2 , I2 (halogens) Higher replaces lower. F2 + HCl
Br2 + KCl
pp. 220, 223
Double Displacement (or Replacement) Reactions
Double Displacement (or Replacement) Reactions
PREDICT THE PRODUCT & BALANCE
1. MgSO4 + LiOH ___________
2. Pb(NO3)2 + Na2CO3 ____________
3. HNO3 + Ba(OH)2 ___________
Answers are on the next slide.
Double Displacement (or Replacement) Reactions
ANSWERS1. MgSO4 + 2 LiOH Mg(OH)2 + Li2SO4
2. Pb(NO3)2 + Na2CO3 PbCO3 + 2 NaNO3
3. 2 HNO3 + Ba(OH)2 Ba(NO3)2 + 2 H2O
Exchange cations
Double Replacement Two things replace each other. Reactants must be two ionic compounds or
acids. Usually in aqueous solution NaOH + FeCl3
The positive ions change place.
NaOH + FeCl3 Fe+3 OH- + Na+1 Cl-1
NaOH + FeCl3 Fe(OH)3 + NaCl
Double Replacement
Has certain “driving forces” Will only happen if one of the products: doesn’t dissolve in water and forms a
solid (a “precipitate”), or is a gas that bubbles out, or is a covalent compound (usually water).
Oxidation and Reduction Reactions
Early chemists saw oxidation as the combination of a material with oxygen
Today, many of these reactions may not even involve oxygen
Redox currently says that electrons are transferred between reactants
Always occur simultaneously. Called redox reactions.
Oxidation and Reduction Reactions
Oxidation – refers to a loss of electrons, or gain of oxygen
Reduction – refers to a gain of electrons, or loss of oxygen
Oxidizing agent – the substance being reduced
Reducing agent – the substance being oxidized
Oxidation and Reduction Reactions Loss of Electrons is Oxidation Gain of Electrons is Reduction
LEO SAYS GER
Rules For Assigning Oxidation States
Oxidation numbers are used to keep track of how many electrons are lost or gained by each atom
Balancing Redox Reactions If the oxidation number changes, that
element has undergone oxidation or reduction
Reaction as a whole must be redox Half-reaction – equation showing just
the oxidation or just the reduction
Balancing Redox Reactions (in an acid)
+4 -2 +7 -2 +6 -2 +2
SO2 + MnO4- →SO4
2- + Mn2+
Divide the equation into half-reactions.
SO2 → SO42- MnO4
- → Mn2+
Oxidation Reduction
Balance all atoms except O and H
Balancing Redox Equations
Balance O by adding H2O.
2H2O + SO2 →SO42- MnO4
- →Mn2+ + 4H2O
Balance H by adding H+.
2H2O + SO2 → SO42- + 4H+
8H+ + MnO4- → Mn2+ + 4H2O
Balance net charge by adding e-.
2H2O + SO2 →SO42- + 4H+ + 2e-
5e- + 8H+ + MnO4- →Mn2+ + 4H2O Step 6.
Make e- gain equal e- loss; then add half-reactions.
5(2H2O + SO2 →SO42- + 4H+ + 2e-)
2(5e- + 8H+ + MnO4- →Mn2+ + 4H2O)
______________________________________10H2O + 5SO2 + 10e- + 16H+ + 2MnO4
- →2Mn2+ + 8H2O + 5SO4
2- + 20H+ + 10e-
Cancel anything that's the same on both sides.
2H2O + 5SO2 +2MnO4- →2Mn2+ +
5SO42- + 4H+
Balancing Redox Reactions (in a base)
Follow steps 1 – 7 then:
8. Identify the number of proton (H+) in the acidic answer. Add the same number of OH+ ions to BOTH sides of the equation.
9. If H+ and OH+ appear on the same side of the equation, they will react in a 1:1 ratio to form H2O.
10. Cancel out water molecules that appear on both sides of the equation.
11. Check that all is balanced
PRECIPITATION REACTIONPRECIPITATION REACTION
A reaction where an insoluble solid is formed during a reaction between two aqueous solutions.
(aq) (aq) + + (aq)(aq) (aq)(aq) + + (s)(s)2KI(aq) + Pb(NO3)2(aq) 2KNO3(aq) +
PbI2(s)Exchange Exchange cationscations
Ionic Equations Many reactions occur in water- that is, in
aqueous solution Many ionic compounds “dissociate”, or separate,
into cations and anions when dissolved in water AgNO3 + NaCl AgCl + NaNO3
1. this is the full equation2. Write it as an ionic equation3. Eliminating ions not directly involved
(spectator ions) = net ionic equation
Molecular, Ionic, Net Ionic Equations
How Do We Predict Solubility?
NEUTRALIZATION REACTIONNEUTRALIZATION REACTION
A reaction between an acid and a base which results in the production of a salt and water.
HA + BOH (metal/nonmetal) + H2O
HNO3(aq) + KOH(aq) KNO3(aq) + H2O(l)
COMBUSTION REACTIONCOMBUSTION REACTION Means “add oxygen” A compound composed of only C, H, and
maybe O is reacted with oxygen If the combustion is complete, the products
will be CO2 and H2O.
If the combustion is incomplete, the products will be CO (possibly just C) and H2O.
A reaction of a substance with oxygen, usually the rapid release of heat produces a flame.
CH + OCH + O22 CO CO22 + H + H22OO
2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g)
Combustion Many times in a combustion reaction,
heat energy is given off. In chemical terms this is called an exothermic reaction.
Thermochemistry is field of chemistry which studies the transfer of heat in a reaction.
The thermodynamic equation representing this exothermic reaction is:
2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g) + heat (in Joules)
Examples
C4H10 + O2 (assume complete)
C4H10 + O2 (incomplete)
C6H12O6 + O2 (complete)
C8H8 +O2 (incomplete)
GAS FORMATION REACTIONSGAS FORMATION REACTIONS A reaction that produces a gas from reactants not
in the gaseous state.
2 HCl (aq) + ZnS (s) ZnCl2 (aq) + H2S (g)
Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2 (g)
Many gas formation reactions involve two steps, first the double displacement reaction then the decomposition reaction of an unstable substance.
NaNa22COCO33 + 2HCl + 2HCl 2 NaCl + H 2 NaCl + H22COCO33
HH22COCO3 3 CO CO22 + H + H22OO
Besides carbonic acid (H2CO3), sulfurous acid (H2SO3) also decomposes into SO2 and water.
COMMON GAS FORMATION REACTIONS COMMON GAS FORMATION REACTIONS YOU SHOULD REMEMBERYOU SHOULD REMEMBER
NH4OH → NH3 (g) + H2O (l)
H2CO3 → CO2 (g) + H2O (l)
H2SO3 → SO2 (g) + H2O (l)
Remember an equation...
Describes a reaction Must be balanced in order to follow
the Law of Conservation of Mass Can only be balanced by changing
the coefficients. Has special symbols to indicate
physical state, and if a catalyst or energy is required.
Table 8-3, p. 223
Examples
H2 + O2
H2O Zn + H2SO4 HgO KBr +Cl2
AgNO3 + NaCl
Mg(OH)2 + H2SO3