A chemical equation is a symbolic representation of all of
the substances involved in a chemical reaction. We use the
chemical formulas of substance to represent each chemical species
involved in the reaction. We also use the notation (g), (l), (s),
or (aq) following the chemical formula to identify the phase of
the substances in the equation.
How do we tell if a chemical reaction occurs? The best
evidence is a difference in the physical and chemical properties
of the reactants and the products. This can be obvious as in the
case of the reaction between iron and sulfur. Other
characteristics to watch for when mixing two or more substances;
heat and light (flames)
explosion
color change
evolution of a gas
formation of a solid (precipitate)
The form of a chemical equation involves writing the formulas
of the reactants (the substances that are mixed together) on the
left, using '+' when more than one substance is involved and the
formula(s) of the product(s) on the right. The reactants and the
products are separated by an arrow '--->'. Sometimes
additional information about the reaction is placed above or
below the arrow which separates the reactants and products. Such
information include;
heat (using a delta symbol)
temperature (at which the reaction is run at)
pressure
time (length of time the reaction is allowed to
proceed)
Neutralization Reactions
-
A reaction between an acid and a base to produce a salt and water. (Remember
you will need to be able to write the ionic and net ionic equations for
these reactions.)
To begin with we need to be able to list some acids and bases that were are
familiar with...here are a few I think everyone should know...already knows
from our discussion in Chapter 6 on nomenclature.
Important Acids
Name
|
Formula
|
Sulfuric acid
|
H2SO4
|
Sulfurous acid
|
H2SO3
|
Nitric acid
|
HNO3
|
Nitrous acid
|
HNO2
|
Phosphoric acid
|
H3PO4
|
Phosphorus acid
|
H3PO3
|
Carbonic acid
|
H2CO3
|
Perchloric acid
|
HClO4
|
Acetic acid
|
HC2H3O2
|
Formula
|
Name
|
HF(aq)
|
Hydrofluoric acid
|
HCl(aq)
|
Hydrochloric acid
|
HBr(aq)
|
Hydrobromic acid
|
HI(aq)
|
Hydroiodic acid
|
H2S(aq)
|
Hydrosulfuric acid
|
HCN(aq)
|
Hydrocyanic acid
|
Important Bases (All of the Group IA and IIA hydroxides)
Name of Base
|
Formula of Base
|
Sodium hydroxide
|
NaOH
|
Potassium hydroxide
|
KOH
|
Barium hydroxide
|
Ba(OH)2
|
Ammonia
|
NH3
|
Calcium hydroxide
|
Ca(OH)2
|
Aluminum hydroxide
|
Al(OH)3
|
Let's consider a few neutralization reactions and how we write the equations.
Consider the reaction between hydrochloric acid and sodium hydroxide;
HCl(aq) + NaOH(aq) --->
To write the products we combine the anion of the acid with the cation of
the base and write the correct formula following the principle of electroneutrality.
The other product is water.
Molecular equation: HCl(aq) + NaOH(aq)
---> NaCl(aq) + H2O(l)
So the molecular form of the equation is shown above. To write the ionic equation
we must separate all aqueous species into their ions and leave any solid, liquid
or gaseous substance in its molecular form. So in this case HCl(aq),
NaOH(aq), and NaCl(aq) must be written as aqueous ions
and H2O(l) remains in its molecualr form.
ionic equation: H+(aq) + Cl-(aq)
+ Na+(aq) + OH-(aq) ---> Na+(aq)
+ Cl-(aq) + H2O(l)
Finally to write the net ionic equation we must cancel all species common
to both sides of the equation
ionic equation: H+(aq) + Cl-(aq)
+ Na+(aq)
+ OH-(aq) ---> Na+(aq)
+ Cl-(aq)
+ H2O(l)
net ionic equation: H+(aq) + OH-(aq)
---> H2O(l)
Consider the reaction between nitric acid and calcium hydroxide;
HNO3(aq) + Ca(OH)2(aq) --->
To write the products we combine the anion of the acid with the cation of
the base and write the correct formula following the principle of electroneutrality.
The other product is water. Be sure to balance this equation.
Molecular equation: 2HNO3(aq) + Ca(OH)2(aq)
---> Ca(NO3)2(aq) + 2H2O(l)
So the molecular form of the equation is shown above. To write the ionic equation
we must separate all aqueous species into their ions and leave any solid, liquid
or gaseous substance in its molecular form. So in this case HNO3(aq),
Ca(OH)2(aq), and Ca(NO3)2(aq) must be written
as aqueous ions and H2O(l) remains in its molecualr form.
ionic equation: 2H+(aq) + 2NO3-(aq)
+ Ca2+(aq) + 2OH-(aq) ---> Ca2+(aq)
+ 2NO3-(aq) + 2H2O(l)
Finally to write the net ionic equation we must cancel all species common
to both sides of the equation
ionic equation: 2H+(aq) + 2NO3-(aq)
+ Ca2+(aq)
+ 2OH-(aq) ---> Ca2+(aq)
+ 2NO3-(aq)
+ 2H2O(l)
net ionic equation: 2H+(aq) + 2OH-(aq)
---> 2H2O(l)
or
net ionic equation: H+(aq) + OH-(aq)
---> H2O(l)
Consider the reaction between hydrobromic acid and ammonia;
HBr(aq) + NH3(aq) --->
To write the products we combine the anion of the acid with the cation of
the base and write the correct formula following the principle of electroneutrality.
The other product is water. Be sure to balance this equation.
Molecular equation: HBr(aq) + NH3(aq)
---> NH4Br(aq)
Notice in this particular neutralization equation no water is formed. Since
there is no hydroxide ions we can not write water as a product. So when ammonia
is one of the reactants we do not include water as a product. Water is present
since the reaction occurs in aqueous solution, we just do not write it as a
product.
So the molecular form of the equation is shown above. To write the ionic equation
we must separate all aqueous species into their ions and leave any solid, liquid
or gaseous substance in its molecular form. So in this case HBr(aq)
and NH4Br(aq) must be written as aqueous ions and NH3(aq)
remains in its molecualr form.
ionic equation: H+(aq) + Br-(aq)
+ NH3(aq) ---> NH4+(aq) + Br-(aq)
Finally to write the net ionic equation we must cancel all species common
to both sides of the equation
ionic equation: H+(aq) + Br-(aq)
+ NH3(aq) ---> NH4+(aq) + Br-(aq)
net ionic equation: H+(aq) + NH3(aq)
---> NH4+(aq)
Consider ONE more reaction, between sulfuric acid and barium hydroxide;
H2SO4(aq) + Ba(OH)2(aq) --->
To write the products we combine the anion of the acid with the cation of
the base and write the correct formula following the principle of electroneutrality.
The other product is water. Be sure to balance this equation.
Molecular equation: H2SO4(aq) + Ba(OH)2(aq)
---> BaSO4(s) + 2H2O(l)
So the molecular form of the equation is shown above. To write the ionic equation
we must separate all aqueous species into their ions and leave any solid, liquid
or gaseous substance in its molecular form. So in this case H2SO4(aq)
and Ba(OH)2(aq) must be written as aqueous ions and BaSO4(s)
and 2H2O(l) remains in their molecualr form.
ionic equation: 2H+(aq) + SO42-(aq)
+ Ba2+(aq) + 2OH-(aq) ---> BaSO4(s)
+ 2H2O(l)
Finally to write the net ionic equation we must cancel all species common
to both sides of the equation. But there are no species common to both sides
of the equation!
net ionic equation: 2H+(aq) + SO42-(aq)
+ Ba2+(aq) + 2OH-(aq) ---> BaSO4(s)
+ 2H2O(l)
So the net ionic equation and the ionic equaton are the same.
Looking at the list of acids and bases at the top of the page
you can imagine ALL the possibilities. So practice a few on your own until you
get comfortable with writing neutralization equations.