Download Chapter 6 – Chemical Reactions: An Introduction

Chemical Equations:
Predicting Types of Reactions and Balancing
I. Chemical Equations
A chemical equation represents a chemical reaction –
1) Chemicals present before the reaction are shown to the left of the arrow
and are called the ______________________.
2) Chemical formed by the reaction are shown to the right of the arrow and
are called the _________________________.
REACTANTS * PRODUCTS
* ________ – indicates direction of change and is read as “yields” or “produces”
Example -
CH4 + 2O2  CO2 + 2H2O
II. Predicting Whether a Reaction Will Occur
A. Four Driving Forces
1) Formation of a _____________ (precipitate)
2) Formation of _______________
3) Transfer of electrons
4) Formation of a _____________
B. If a driving force occurs the reaction will take place.
III. Types of Reactions
A. Double Displacement:
Reactants are:
B. Single Displacement:
Reactants are:
C. Decomposition:
Reactants are:
D. Synthesis:
Reactants are:
E. Combustion:
Reactants are:
Double Displacement Reactions
Precipitation Reaction: Double Displacement reactions where the driving force
is formation of a __________________________.
Acid-Base/ Neutralization Reaction: Double Displacement reactions where
the driving force is formation of a __________________. (water)
F. Oxidation-Reduction reactions: (redox)
 Driving Force = Transfer of electrons
 Always in single displacement reactions
 Sometimes in Synthesis and Decomposition
 Never in Double Displacement
Example:
2 NaCl (aq)  2 Na (s) + Cl2 (g)
2 Na (s) + Cl2 (g)  2 NaCl (aq)
Zn(NO3)2(aq) + 2 Na(s)  2NaNO3(aq) + Zn(s)
Learning Check: Classify the following reactions:
2 KNO3
 2 KNO2 + O2
2 C2H2 + 5 O2  4 CO2 + 2 H2O
CaO + H2SO4  CaSO4 + H2O
3 CaCl2 + 2 Na3PO4  Ca3(PO4)2(s) + 6 NaCl
2 Fe + 6 HC2H3O2  2 Fe(C2H3O2)3 + 3 H2
2 KCl + 3 O2  2 KClO3
IV. Evidence of Chemical Reactions
Four indicators a chemical reaction has occurred:
1) Color change; __________________
2) Precipitate forms; _______________________
3) Gas forms; ______________________
4) Heat is produced or absorbed; ___________________

The reactants and the products contain the same atoms, but the chemical
reaction has changed the way they are grouped.

In a chemical reaction, atoms are neither created nor destroyed; all atoms
present in the reactants must be present in some form in the products. This
is the ______________________________________

There must be the same number of each type of atom on both sides of the
equation.

Balancing an equation makes sure that there is the same number and type of
atom on both sides of the equation.

The chemical equation for a reaction provides us with three important pieces
of information:
1) Identities of the reactants and products
1) Relative numbers of each atom
2) State of each reactant and product
States of matter are shown with the following symbols:
(s) solid
(l) liquid
(g) gas
(aq) aqueous, dissolved in water
V. Balancing Chemical Equations
 Use ___________________ to make sure you have the same number of each
atom on either side of the equation.
 Identities of the compounds must never be changed when balancing. YOU
CAN NEVER CHANGE A SUBSCRIPT IN A FORMULA!!!!!

Most chemical equations can be balanced by trial and error.
STEPS –
1. Write the unbalanced equation, making sure the formulas of the
compounds are correct.
2. Don’t forget the ________________ – BrINClHOF if they appear by
themselves they must be written as Br2, I2, N2, Cl2, H2, O2, F2,
3. Use _______________ in front of each substance to balance. The
coefficient, 1, is never written.
4. The best balanced equation is the one with the ______________ ratio of
coefficients.
5. DOUBLE CHECK YOUR WORK!!!!
HINTS : 1) Make odd numbers of atoms even.
2) Balance oxygen and hydrogen last.
3) If a polyatomic ion doesn’t change in the reaction count it as a
group.
Examples –
1) Reaction of hydrogen gas and oxygen gas to form liquid water.
2) Liquid ethanol, C2H5OH, reacts with oxygen gas to produce carbon dioxide
gas and water vapor.
3) Solid potassium reacts with liquid water to form hydrogen gas and
potassium hydroxide that dissolves in water.
LEARNING CHECK: Nitrogen trihydride gas reacts with oxygen gas to produce
nitrogen monoxide gas and water vapor.
Examples:
1)
C3H8(g)
+
2)
NH4NO2(s)

3)
NO(g)
N2O(g)

O2(g)
N2(g)
LEARNING CHECK
HNO3(aq) 
NO2(g)
Mg(s)
+
H2O(l)


+
+
CO2(g)
+
+
H2O(g)
H2O(g)
NO2(g)
H2O(l)
Mg(OH)2(s)
+
O2(g)
+
H2(g)
VI. Predicting States of Substances
A. Terms
1. Soluble solid – readily dissolves in water
2. Insoluble and slightly soluble solid – a solid where such a tiny
amount dissolves in water that it is undetectable to the naked eye
3. Solubility is temperature dependent
B. Solubility Rules (back of snoopy sheet)
Mainly water soluble (aq)
1. All nitrates are soluble.
2. All acetates are soluble.
3. All chlorates are soluble.
4. All chlorides are soluble except AgCl, Hg2Cl2, and PbCl2
5. All bromides are soluble except AgBr, Hg2Br2, PbBr2, and HgBr2
6. All iodides are soluble except AgI, Hg2I2, PbI2, and HgI2
7. All sulfates are soluble except CaSO4, SrSO4, BaSO4, PbSO4,
Hg2SO4, and Ag2SO4
Mainly water insoluble (s)
 All sulfides are insoluble except those of 1A and 2A elements and
(NH4)2S
 All carbonates are insoluble except those of 1A and (NH4)2CO3
 All phosphates are insoluble except those of 1A and (NH4)3PO4
4. All hydroxides are insoluble except those of 1A, Ba(OH)2, Sr(OH)2
and Ca(OH)2
Ex. Predict whether the following substances are soluble or insoluble.
LEARNING CHECK: Determine if the following are AQUEOUS or SOLID
1. lead (II) nitrate
2. potassium sulfide
3. barium hydroxide
4. ammonium carbonate
C. Special rules
1. Acids are aqueous
2. Most metal oxides are solids
3. Most non-metal oxides are gases
4. Elements:
 Liquids: Hg & Br2
 Gases: H2, N2, O2, F2, Cl2 and Noble Gases
 Solid: all other elements
5. State (l) is reserved for pure liquids – H2O, and some hydrocarbons
LEARNING CHECK: Determine the state:
1. lead(II) phosphate
2. magnesium oxide
3. nickel
4. dinitrogen monoxide
5. chlorine
6. sulfuric acid
7. sodium sulfide