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;

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;

Neutralization 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.