Chemical Equation Summary

We will employ chemical equations as a symbolic way of representing a chemical reaction.

We have looked at five kinds of chemical reactions. You will need to able to recognize the different types of reactions and to write the correct products give the reactants. We will see examples of the different types of reactions in class. You must know these examples for the examination. You will also be expected to extend the information you receive in class to other examples.

The five different reaction types are;

Formation

• A reaction between elements in their standard state to form a single product in its standard state. Such reactions may require heat or other form of energy to occur.

• Fe_(s) + S_(s) -(heat)--> FeS_(s)

• Al_(s) + Br_2(s) ---> Al₂Br_6(s)

Combustion

• A reaction between a substance and oxygen. The common example is the combustion of a hydrocarbon. A hydrocarbon is a covalent (organic) compound which only contains carbon and hydrogen. The combustion of a hydrocarbon produces carbon dioxide (CO₂) and water (H₂O)

• CH_4(g) + O_2(g) ---> CO_2(g) + H₂O_(g)

Double replacement

• A reaction between two ionic compounds producing two new ionic compounds where the cations and anions have exchanged 'partners'. You must use the Solubility Table to predict solubility. (Remember you will need to be able to write the ionic and net ionic equations.)

• NaCl_(aq) + AgNO_3(aq) ---> NaNO_3(aq) + AgCl_(s)

Neutralization

• 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.)

• HCl_(aq) + NaOH_(aq) ---> NaCl_(aq) + H₂O_(g)

Single replacement

• A reaction in which an element in a reactant compound is replaced by a second reacting element producing a new compound and an element. (Remember you will need to be able to write the ionic and net ionic equations.)

• Na_(s) + H₂O_(l) ---> NaOH_(aq) + H_2(g)

• Mg_(s) + 2HCl_(aq) ---> MgCl_2(aq) + H_2(g)

• Zn_(s) + Cu(NO₃)_2(aq) ---> Zn(NO₃)_2(aq) + Cu_(s)

Important Acids

Important Bases (All of the Group IA and IIA hydroxides)

How to balance equations

One very important aspect of any chemical equation is that it be balanced. While the process of balancing chemical equations is straight forward, the real challenge is in the laboratory trying to identify the products of a chemical reaction. In this course our goal will generally be to simply balance a chemical equation. The primary rule that must be remembered when balancing equations is not to change subscripts in the formulas. Balancing equations is accomplished by changing coefficients. Coefficients are whole numbers immediately preceding the chemical formula for the substance in the equation. Never change a subscript or add or remove elements or compounds in an equation.

__Fe(s) + __S₈(s) ----> __FeS(s)

To balance this equation, that is, obtain equals numbers of atoms of each element in the products and the reactants, can be accomplished by placing a coefficient of 8 in front of iron(II) sulfide, and than a 8 in front of iron. Now the equation is balanced.

There are some simple rules for balancing equations:

• Things not to do when balancing an equation:

  1. Change a subscripted number

  2. Add or remove an element arbitrarily

  3. Add or remove a compound arbitrarily

• Things to do when balancing an equation:

  1. Change only the coefficients preceding an element or compound.

  2. Try to balance non-oxygen and non-hydrogen elements first.

  3. Balance substances in their elemental form last.