Download Chapter 11 Chemical Reactions

Chapter 11 – Chemical Reactions
I.
Definition of a chemical equation
A.
Chemical reaction definition: any interaction among chemical substances
that brings about some change.
B.
How do we know that a chemical change has occurred?
1.
Gas production.
2.
Heat production/absorption.
3.
Permanent change in color.
4.
Appearance of a precipitate. A precipitate is an insoluble
substance, this means you see a powder form on the bottom of the
beaker or flask.
C.
Chemical Equation definition: a method for expressing a chemical
reaction in symbols and formulas.
1.
We must know how the substances react and what they form to
write a chemical equation.
2.
Every chemical equation must be balanced. The number of atoms
on the left side must equal the number of atoms right side.
a.
Law of Conservation of Mass. The concentration of mass
says that matter is neither created nor destroyed in a
chemical reaction. In other words, you cannot create or
destroy matter in a chemical reaction.
3.
They can be written as complete equations or ionic equations.
II.
Terms, Symbols and their meanings.
A.
Reactants: substances which interact, written on the left side.
B.
Products: substances that are formed, written on the right side.
C.
Single arrow : goes in one direction (direction of the arrow).
D.
Double arrow: goes in both directions – reversible.
E.
(g), (l), (s), (aq): gas, liquid, solid, solution is dissolved in water,
respectively.
F.
: heat.
G.
Catalyst: any substance that increases the rate of a chemical reaction, but
is recovered unchanged at the end of the reaction.
1.
Usually written above or below the arrow.
III.
Guidelines for balancing equations
A.
There are various ways to balance equations. These guidelines are
generally applicable for most of the chemical equations you will encounter
in this class.
1.
Write the correct formulas for the reactants and the products.
a.
Once you have the correct formula, you will not change it
during the balancing process. Instead, you will add
coefficients in front of the formula to obtain a balanced
equation.
2.
3.
4.
5.
6.
Begin the process by selecting a specific element to balance.
a.
Generally, you select an element from the compound that
has the greatest number of atoms. Also, you select the
element present in the largest number, excluding hydrogen
and oxygen and polyatomic ions that remain the same on
both sides of the equation.
Balance the polyatomic ions that remain the same on both sides of
the equation.
Balance the H and then the O atoms, which were not balanced in
Step 3.
Check all the coefficients to make certain that they are whole
numbers and in the lowest possible ratio.
Check to make certain that it is balanced.
Example:
Calcium hydroxide + phosphoric acid  calcium phosphate + water
Ca(OH)2(aq) + H3PO4(aq)  Ca3(PO4)2(s) + H2O(l)
Ca = 1
H=3
PO4 = 1
OH = 2
Ca = 3
H=2
PO4 = 2
OH = 1
3 Ca(OH)2(aq) + 2 H3PO4(aq)  Ca3(PO4)2(s) + 6 HOH(l)
Ca = 3
H=6
PO4 = 2
OH = 6
Ca = 3
H=6
PO4 = 2
OH = 6
IV.
Examples
a):
Fe(s) + HCl  FeCl2(aq) + H2(g)
Fe(s) + 2 HCl  FeCl2(aq) + H2(g)
b):
C4H10(g) + O2  CO2 + H2O (fraction coefficient)
C4H10(g) + 13/2O2  4 CO2 + 5 H2O
 2 C4H10(g) + 13 O2  8 CO2 + 10 H2O
V.
Five types of sample chemical equations
A.
Combination:
A + Z  AZ
B.
Decomposition:
AZ  A + Z
C.
Single Replacement reactions:
A + BZ  AZ + B
X + BZ  BX + Z
D.
Double displacement reactions:
AX + BZ  AZ + BX
E.
Neutralization reactions:
HX + MOH  MX + HOH