View
212
Download
0
Embed Size (px)
Citation preview
1
2
• Chemists use chemical equations to describe reactions they observe in the laboratory or in nature.
• Chemical equations provide us with the means to
1. summarize the reaction
2. display the substances that are reacting
3. show the products
4. indicate the amounts of all component substances in a reaction.
3
The Chemical EquationThe Chemical Equation
4
• Chemical reactions always involve change.
• Atoms, molecules or ions rearrange to form new substances.
• The substances entering the reaction are called reactants.
• The substances formed in the reaction are called products.
• During reactions chemical bonds are broken and new bonds are formed.
5
• A chemical equation uses the chemical symbols and formulas of the reactants and products and other symbolic terms to represent a chemical reaction.
• A chemical equation is a shorthand expression for a chemical change or reaction.
6
Balancing Equations
___W8 + ___B12 ___WBWB___W8 + ___B12 ___WBWB
•ReactantsReactants •ProductsProducts
Making Hot dogs:How many packages wieners & buns to buy so none is left over.
33 22 2424
http://www.youtube.com/watch?v=oYIHLUxzRr8
7
Al + Fe2O3 Fe + Al2O3
reactants productsAl + Fe2O3 Fe + Al2O3
Chemical Equation
iron oxygen bonds break
aluminum oxygen bonds form
8
Coefficients (whole numbers) are placed in front of substances to balance the equation and to indicate the number of units (atoms, molecules, moles, or ions) of each substance that is reacting.
9
Al + Fe2O3 Fe + Al2O3
coefficient2 2
coefficient
10
Conditions required to carry out the reaction may be placed above or below the arrow.
11
Al + Fe2O3 Fe + Al2O3
coefficient2 2
coefficient
heat
12
The physical state of a substance is indicated by symbols such as (l) for liquid.
13
2Al(s) + Fe2O3(s) 2Fe(l) + Al2O3 (s)
All atoms present in the reactant must also be present in the products.
In a chemical reaction atoms are neither created nor destroyed.
(s) (l) (s)(s)
14
Symbols UsedSymbols Usedin Chemical Reactionsin Chemical Reactions
Symbols UsedSymbols Usedin Chemical Reactionsin Chemical Reactions
15
placed between substances
+symbol
plusmeaning
location
16
placed between substances
symbol
resonancemeaning
location
17
symbol
yieldsmeaning
between reactants and products
location
18
symbol
equilibriummeaning
between reactants and products
location
19
(s)symbol
solidmeaning
after formulalocation
20
(l)symbol
liquidmeaning
location after formula
21
(g)symbol
gasmeaning
location after formula
22
(aq)symbol
aqueousmeaning
after formulalocation
23
symbol
heatmeaning
written above location
24
hsymbol
light energymeaning
written above location
25
symbol
gas formationmeaning
after formulalocation
26
symbol
precipitate formation
meaning
after formulalocation
27
Writing andWriting andBalancing EquationsBalancing Equations
28
• To balance an equation, adjust the number of atoms of each element so that they are the same on each side of the equation.
• Golden Rule of Balancing:
Balance with coefficients only!
Do not mess with the subscripts!!!
29
Steps for Steps for Balancing EquationsBalancing Equations
Steps for Steps for Balancing EquationsBalancing Equations
30
Step 1 Identify the reaction. Write a description or word equation for the reaction.
Mercury(II) oxide decomposes to form mercury and oxygen.
mercury(II) oxide → mercury + oxygen
31
HgO Hg + O2
– The formulas of the reactants and products must be correct.
– The reactants are written to the left of the arrow and the products to the right of the arrow.
Step 2 Write the unbalanced (skeleton) equation.
The formulas of the reactants and products can never be changed.
32
Step 3a Balance the equation.– Count and compare the number of atoms of each
element on both sides of the equation.
– Determine the elements that require balancing.
33
2HgO 2Hg + O2
THE EQUATION IS BALANCED
34
sulfuric acid + sodium hydroxide → sodium sulfate + water
Balance the Equation
35
H2SO4(aq) + NaOH(aq) → Na2SO4(aq) + H2O(l)2
Balance the Equation
36
H2SO4(aq) + NaOH(aq) → Na2SO4(aq) + H2O(l)2 2
THE EQUATION IS BALANCED
37
butane + oxygen → carbon dioxide + water
Balance the Equation
38
C4H10 (g) + O2 (g) → CO2(g) + H2O(l)4
Balance the Equation
39
C4H10 (g) + O2 (g) → CO2(g) + H2O(l)4 5
40
C4H10 (g) + O2 (g) → CO2(g) + H2O(l) 4 513 2
Remove fractions by multiplying by the lowest common multiple
41
C4H10 (g) + O2 (g) → CO2(g) + H2O(l)1052 8 10
THE EQUATION IS BALANCED
13
42
What Information Does What Information Does an Equation Tell Us?an Equation Tell Us?
43
The meaning of a formulais context dependent.
The formula H2O can mean:
1. 2 H and 1 O atom
2. 1 molecule of water
3. 1 mol of water
4. 6.02 x 1023 molecules of water
5. 18.02 g of water
44
In an equation formulas can represent units of individual chemical entities or moles.
H2 + Cl2 2HCl→
1 molecule H2 1 molecule Cl2 2 molecules HCl
1 mol H2 1 mol Cl2 2 mol HCl
45
FormulasNumber of molecules
Number of atomsNumber of molesMole weights
46
Types of Chemical Types of Chemical EquationsEquations
47
Combination (synthesis) Decomposition (analysis) Single-Displacement (substitution) Double-Displacement (metathesis) Combustion (oxidation)
48
Combination ReactionsCombination ReactionsCombination ReactionsCombination Reactions
49
A + B AB
Two reactants combine to form one product.
50
ExamplesExamples
51
2Ca(s) + O2(g) 2CaO(s)
Metal + Oxygen → Metal Oxide
4Al(s) + 3O2(g) 2Al2O3(s)
52
S(s) + O2(g) SO2(g)
Nonmetal + Oxygen → Nonmetal Oxide
N2(g) + O2(g) 2NO(g)
53
2K(s) + F2(g) 2KF(s)
Metal + Nonmetal → Salt
2Al(s) + 3Cl2(g) 2AlCl3(s)
54
Na2O(s) + H2O(l) 2NaOH(aq)
Metal Oxide + Water → Metal Hydroxide
CaO(s) + 2H2O(l) 2Ca(OH)2(aq)
55
SO3(g) + H2O(l) H2SO4(aq)
Nonmetal Oxide + H2O(l) → Oxy-acid
N2O5(g) + H2O(l) 2HNO3(aq)
56
Decomposition ReactionsDecomposition ReactionsDecomposition ReactionsDecomposition Reactions
57
AB A + B
A single substance breaks down togive two or more different substances.
58
ExamplesExamplesExamplesExamples
59
2Ag2O(s) 4Ag(s) + O2(g)
Metal Oxide → Metal + Oxygen
Metal Oxide → Metal Oxide + Oxygen
2PbO2(s) 2PbO(s) + O2(g)
60
Carbonate → CO2(g)
CaCO3(s) CaO(s) + CO2(g)
2NaHCO3(s) Na2CO3(s) + H2O(g) + CO2(g)
Hydrogen carbonate → CO2(g)
61
Miscellaneous Reactions
2KClO3(s) 2KCl(s) + O2(g)
2NaNO3(s) 2NaNO2(s) + O2(g)
2H2O2(l) 2H2O(l) + O2(g)
62
Single Displacement Single Displacement ReactionsReactions
Single Displacement Single Displacement ReactionsReactions
63
A + BC AC + B
One element reacts with a compound toreplace one of the elements of that compound.
64
Mg(s) + HCl(aq) H2(g) + MgCl2(aq)
2Al(s) + 3H2SO4(aq) 3H2(g) + Al2(SO4)3(aq)
salt
Metal + Acid → Hydrogen + Salt
salt
65
Na(s) + 2H2O(l) H2(g) + NaOH(aq)
Ca(s) + 2H2O(l) H2(g) + Ca(OH)2(aq)
Metal + Water → Hydrogen + Metal Hydroxide
metal hydroxide
metal hydroxide
66
Metal + Water → Hydrogen + Metal Oxide
metal oxide
Fe(s) + 4H2O(g) 4H2(g) + Fe3O4(s)
74
Double Displacement Double Displacement ReactionsReactions
Double Displacement Double Displacement ReactionsReactions
75
AB + CD AD + CB
Two compounds exchange partners with each other to produce two different compounds.
The reaction can be thought of as an exchange of positive and negative groups.
A displaces C and combines with DB displaces D and combines with C
76
The Following Accompany Double Displacement Reactions
• formation of a precipitate
• release of gas bubbles
• release of heat
• formation of water
77
ExamplesExamples
78
Acid Base Neutralization
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l)
acid + base → salt + water
79
Formation of an Insoluble Precipitate
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)
↓
↓
80
Metal Oxide + Acid
CuO(s) + 2HNO3(aq) Cu(NO3)2(aq) + H2O(l)
CaO(s) + 2HCl(aq) CaCl2(s) + H2O(l)
metal oxide + acid → salt + water
81
Formation of a Gas
H2SO4(aq) + 2NaCN(aq) Na2SO4(aq) + 2HCN(g)
NH4Cl(aq) + NaOH(aq) NaCl(aq) + NH4OH(aq)
NH4OH(aq) NH3(g) + H2O(l)
indirect gas formation
↑
↑
82
Combustion ReactionsCombustion ReactionsCombustion ReactionsCombustion Reactions
83
Hydrocarbon reacts with oxygen to produce carbon dioxide and water
84
ExamplesExamples
85
Combustion of Methane
CH4 (g) + O2 (g) CO2 (g) + H2O (l)
Balance by first balancing C, then H, and finally O
86
1 CH4 (g) + O2 (g) 1 CO2 (g) + H2O (l)
1 CH4 (g) + O2 (g) 1 CO2 (g) + 2 H2O (l)
1 CH4 (g) + 2 O2 (g) 1 CO2 (g) + 2 H2O (l)
87
Combustion of Ethane
C2H6 (g) + O2 (g) CO2 (g) + H2O (l)
Balance by first balancing C, then H, and finally O.Use fractions if needed to balance, then change to whole numbers.
88
1 C2H6 (g) + O2 (g) 2 CO2 (g) + H2O (l)
1 C2H6 (g) + O2 (g) 2 CO2 (g) + 3 H2O (l)
1 C2H6 (g) + O2 (g) 2 CO2 (g) + 3 H2O (l)
7
2
2 C2H6 (g) +7 O2 (g) 4 CO2 (g) + 6 H2O (l)
98