Chapter 8: Chemical Equations and Reactions
1. List signs of a chemical change
2. Correctly write a chemical equation
3. Balance a chemical equation
Indications of Chemical Reaction
• Temperature change
• Formation of a gas
• Formation of a precipitate (insoluble)
• Color change
Chemical Equations
• Represent known facts
• Contain correct formulas for reactants and products
• Satisfies law of conservation of mass
Subscripts can NEVER be changed
Coefficients CAN be changed
Word and Formula Equations
Word Equation
methane + oxygen carbon dioxide + water
Formula Equation
CH4(g) + O2(g) CO2(g) + H2O(g)
Additional Symbols
→ - “yields”
↔ - reversible reaction
↑ - gaseous product; also (g)
↓ - precipitate
(s) – solid
(l) – liquid
(aq) – aqueous; dissolved in water
Meaning of a Chemical Equation
1. Coefficients represent relative amounts of reactants
2. Relative masses of reactants and products can be determined from coefficients
3. The reverse reaction has the same relative amounts of substances as forward reaction
Balancing Equations
• Balance elements one at a time
• Balance polyatomic ions as single units
• Balance atoms that appear only once on each side first
• Balance hydrogen and oxygen last
Types of Reactions
1. Give general equations for types of reactions
2. Classify reactions3. List 3 types of synthesis
and 6 decomposition reactions
4. List 4 types of single-replacement and 3 types of double-replacement reactions
5. Predict products of reactions given the reactants
Synthesis Reactions
General Formula:
A + X AX
Synthesis with Oxygen
With metals form metal oxides
Ex – Mg(s) + O2(g) MgO(s)
K(s) + O2(g) K2O(s)
2Fe(s) + O2(g) 2FeO(s)
4Fe(s) + 3O2(g) 2Fe2O3
S8(s) + 8O2(g) 8SO2(g)
C(s) + O2(g) CO2(g)
Synthesis with Sulfur
With metals produce metal sulfides
Ex- 16Rb(s) + S8(s) 8Rb2S(s)
8Ba(s) + S8(s) 8BaS(s)
Metals with Halogens
Group 1: M + X2 2MX
Ex – Na(s) + Cl2(g) 2NaCl(s)
Group 2: M + X2 MX2
Ex – Mg(s) + F2(g) MgF2(s)
Metal Oxides with Water
Group 1 & 2 form hydroxides
Ex – K2O(s) + H2O(l) 2KOH(aq)
CaO(s) + H2O(l) Ca(OH)2(l)
Non-metal Oxide with Water
Form oxyacidsEx – SO2(g) + H2O(l) H2SO3(aq)
P2O5(s) + 3H2O(l) 2H3PO4(aq)
Decomposition Reactions
AX A + X
Decomposition of Binary Compounds
Breaks down into its elements
(g)O (g)2H O(l)2H 22yelectricit
2
Process called electrolysis
Decomposition of Metal Carbonates
Form metal oxides and carbon dioxide
(g)CO CaO(s) (s)CaCO 23
Decomposition of Metal Hydroxides
Form metal oxides and water
O(g)H CaO(s) (s)Ca(OH) 22
Decomposition of Acids
Break down into non-metal oxides and water
O(g)H (g)CO (aq)COH 2232
O(l)H (g)SO (aq)SOH 2342
Single Replacemen
t
General Formula
A + BX AX + B
Metal Replaces Another Metal
Aluminum is more reactive than lead
(aq))2Al(NO 3Pb(s)
(aq))Pb(NO 2Al(s)
33
23
Replacement of Hydrogen in Water by a Metal
More Active Metals
(g)H 2NaOH(aq) O(l)2H 2Na(s) 22
Less Active Metals(g)4H (s)OFe O(g)4H 3Fe(s) 2432
Replacement of Hydrogen in an Acid by a Metal
Metals more active than hydrogen
(aq)MgCl (g)H 2HCl(aq) Mg(s) 22
Replacement of Halogens
Each halogen can replace the halogen below it on the periodic table
reaction no 2NaCl(aq) (g)I
(g)Cl 2KF(aq) 2KCl(aq) (g)F
(g)Br 2KCl(aq) 2KBr(aq) (g)Cl
2
22
22
Double Replacement
AX + BY AY + BX
Formation of a precipitate
Formation of a gas
Formation of water
Formation of a Precipitate
An insoluble product forms
(aq)2KNO (s)PbI (aq))Pb(NO KI(aq)2 3223
Formation of a Gas
Insoluble gas forms
Example
(aq)FeCl S(g)H 2HCl(aq) FeS(s) 22
Formation of Water
Water forms during reaction
Combustion Reaction
Substance reacts with oxygen to release heat and light
Products are often carbon dioxide and water
Neutralization Reaction
HA + BOH AB + HOH
Usually these are acid-base reactions
Products include salt and water
Types of Rxn Lab Due Friday
That’s 10-31-08 if you’re wondering…
Activity Series
1. Explain the significance of an activity series
2. Use an activity series to predict if a reaction will take place
Metals vs. Nonmetals
Greater activity of a metal indicates how easily it loses electrons
Greater activity of a nonmetal indicates how easily it gains electrons
In a single-replacement reaction, if an element with lower activity is to be replaced, the reaction will take place.