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.