Chapters 8.1-8.6

8.1 Chemical Equations

   Chemical Equations are a written way of

describing a chemical change. The general

format for chemical equations is:

1. An arrow separates the reactants

from the products.

Ca + Cl₂ CaCl₂

2. A plus sign (+) is placed between reactants

or products as needed.

3. Coefficients as integrals are placed before

a substance to indicate the number of units

needed in the balanced reaction.

2H₂ + O₂ 2H₂O

4. Conditions for the reaction are written

symbolically above the arrow. This includes

any catalysts that are required for the reaction.

5. The physical state of the substance is

indicated by a letter following the symbol of

the element and put in parenthesis.

8.2 Writing / Balancing Chemical Equations

   A balanced chemical equation conforms

with the concept of conservation of "matter".

"All atoms that appear on the left side of the

equation must also appear on the right side of

the equation".

Balancing equations involves finding the

smallest whole number multiplier for each

compound that will result in the left side of the

equation having the same type and number

of atoms as the right side. The following steps

can be used as a guide.

Step 1: Write the unbalanced chemical reaction.

Step 2: Choose a molecule on either side of the

equation that appears to be "the most complex".

Step 3: Make the coefficient of that molecule 1.

Step 4: Balance each of the atoms in the chosen

molecule first.

Step 5: If fractions were used then multiply every

coefficient in the equation with " the denominators

of the fraction".

Example: Complete oxidation of methyl alcohol and

water.

Step 1: Write the unbalanced chemical reaction.

Step 2:" Chose a molecule on either side of the

equation which appears to be the most complex".

In this case methyl alcohol.

Step 3: Make the coefficient of that molecule 1.

Step 4: Balance each of the atoms in the chosen

molecule first. How many C are needed to set

them equal on both sides? Now look at the H, note

the change necessary on the left to balance with

the right. Go ahead and write the coefficient 2 in

front of the H₂O. The last thing to consider is the

oxygen's. At times this can be tricky and you may

need to work with fractions to get the desired

result.

Step 5: This step was not necessary in our

example, however in more complex reactions

it provides a much simpler means to an end.

8.3 Information Given in a Chemical Equation

   1. The reactants

    2. The products

    3. The amounts of each item used and

produced

    4.The physical state of each item

8.4 Types of Chemical Reactions

   Combination   A+B C

Exp:  4Fe + 3O₂ 2Fe₂O₃

   Combustion   

CH₄ + 2O₂ CO₂ + 2H₂O

This type of reaction is actually a

part of the general oxidation-reduction

reactions where in this case the oxygen

gas is the oxidizing agent and the

substance under going the combustion

is the reducing agent.

    Decomposition   AB A+B

Exp:  H₂O₂ H₂O + O₂

A decomposition reaction results when

a substance is broken down into simpler

substances.

    Single Replacement
                      AB+C AC+B

Exp: 

CuCl₂(aq) + Zn(s) Cu(s) + ZnCl₂

This is an example of an oxidation reduction

reaction where the zinc is the reducing agent

and the copper(II) ion is the oxidizing agent.

    Double Replacement
                       AB+CD AD+CB

Exp:

Formation of water in a neutralization

reaction.

NaOH(aq) + HCl(aq) NaCl(aq) + HOH₁

_{Formation of an insoluble product.}

2KS(aq) + CaCl(aq) CaS(s) + 2KCl(aq)

8.5 Heat in Chemical Equations

   By nature reactions strive to attain the

lowest possible energy state. If the reaction

occurs, energy is released to the

surroundings and the product is stabilized.

Exp: A gas mower which burns gas thereby

releasing energy in the form of not only

heat but work which drives the mower.

Two Reaction Types

1. Endothermic- absorbs heat

2. Exothermic- releases heat

Heat of Reaction is the amount of heat

measured in kilojoules or kilocalories

that is generated by the reaction.

8.6 Global Warming /Greenhouse Effect

   A very delicate balancing act between

man and nature is the best prevention.

Before the industrial revolution remained

at a constant level. Now the dramatic

increase in carbon dioxide(CO₂) from

the increased burning of oil, coal, and

wood we our like a world trapped in a

jar.      CO₂ slows down

movement of heat trapping heat near

earth and increasing the temperature.

Plants are helpful place to store carbon

dioxide, and until the increase of fossil

fuel usage they were effective. However,

increased population use and deforestation

of our rain forests, this is a battle we made

by ourselves.