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Chemistry and all other
sciences are based on facts established through experimentation. A scientific
law is a condensed statement of facts which has been discovered by experiment. There are three basic laws
that apply to chemical reactions. They are the Law of Conservation of Mass, the
Law of Definite Proportions, and the Law of Multiple Proportions. These laws
are described here to help the reader in understanding the reasons elements and
compounds behave as they do. 1.The Law of Conservation of Mass This law states that in a
chemical reaction the total mass of the products equals the total mass of the
reactants. Antoine Lavoisier, a French chemist, discovered that when tin reacts
with air in a closed vessel, the weight of the vessel and its contents is the
same after the reaction as it was before. Scientists later discovered that
whenever energy (heat, light, radiation) is liberated during a reaction, a very
small change in mass does occur, but this change is insignificant in ordinary
chemical reactions. 2.The Law of Definite Proportions This law states that no
matter how a given chemical compound is prepared, it always contains the same
elements in the same proportions by mass. John Dalton, an English physicist,
discovered that when various metals are burned or oxidized in air, they always
combine in definite proportions by weight. For example, one part by
weight of oxygen always combines with 1.52 parts by weight of magnesium or 37.1
parts by weight of tin. This law results from the fact that a compound is
formed by the combination of a definite number of atoms of one element with a
definite number of atoms of another. 3.The Law of Multiple Proportions This law states that if
two elements combine to form more than one compound, the masses of one of the
elements combining with a fixed mass of the other are in a simple ratio to one
another. For example, carbon forms two common compounds with oxygen; carbon
monoxide and carbon dioxide. With carbon monoxide (CO), 1.33 grams of oxygen
are combined with 1 gram of carbon. With carbon dioxide (CO2), 2.67
grams of oxygen are combined with 1 gram of carbon. Therefore, the masses of
oxygen combining with a fixed mass of carbon are in the ratio 2:1. Combining Elements The Laws of Definite
Proportions and Multiple Proportions and the related portions of atomic theory
form the bases for most quantitative calculations involving chemical reactions.
Applying the basic chemical laws to chemical bonding will help the reader to
understand the probability and proportions involved in chemical reactions.
Regardless of the type of bond (ionic, covalent, coordinate covalent, or
metallic), specific amounts of one element will react with specific amounts of
the element(s) with which it is combined. If two substances are placed
together in a container, in any ratio, the result is a mixture. When a teaspoon of sugar is added to a glass of water, it will slowly
dissolve into the water and disappear from view. As a result, the molecules of
sugar are evenly distributed throughout the water and become mixed with the
water molecules. Because the sugar and water mixture is uniform throughout, it
is said to be homogeneous. A homogeneous mixture of two or more substances is
called a solution. The reason solutions are classified as mixtures
rather than as compounds is because the composition is not of fixed proportion. All solutions consist of a
solvent and one or more solutes. The solvent
is the material that dissolves the other
substance(s). It is the dissolving medium. In the water-sugar solution, the
water is the solvent. The substances that dissolve in the solution are called solutes. In the water-sugar solution, sugar is the solute. It is not always easy
to identify which is the solvent and which is the solute (for example, a solution
of half water and half alcohol). Solutions can exist in any
of the three states of matter, solid, liquid, or gas. The earth's atmosphere is
a gaseous solution of nitrogen, oxygen, and lesser amounts of other gases. Wine
(water and alcohol) and beer (water, alcohol, and CO2) are examples
of liquid solutions. Metal alloys are solid solutions (14-karat gold is gold
combined with silver or copper). One factor that determines
the degree and/or rate at which a reaction takes place is solubility. Solubility is defined as the maximum amount of a substance that can dissolve in a
given amount of solvent at a specific temperature. At this point, the solution
is said to be saturated. A solution is saturated when equilibrium is
established between the solute and the solvent at a particular temperature. Equilibrium is the point at which the rates of the forward and reverse reactions are
exactly equal for a chemical reaction if the conditions of reaction are
constant. Kinetics is the study of
the factors which affect the rates of chemical reactions. There are five
principle factors to consider: concentration, temperature, pressure, the nature
of the reactants, and the catalyst. Summary The important information
in this chapter is summarized below. Chemical Bonding Summary The following terms are
defined in this chapter: An ionic bond occurs where
one or more electrons are wholly transferred from one element to another, and
the elements are held together by the force of attraction due to the opposite
polarity of the charge. The van der Waals forces
are attractions between the molecules of nonpolar covalent substances. These
forces are generally believed to be caused by a temporary dipole, or unequal
charge distribution, as electrons constantly move about in an atom, ion, or
molecule. A covalent bond is a bond
in which one or more electrons from an atom pair off with one or more electrons
from another atom and form overlapping electron shells in which both atoms
share the paired electrons. Metallic bonds are bonds
where the atoms achieve a more stable configuration by sharing the electrons in
their outer shell with many other atoms. A mixture is defined as
two substances placed together in a container, in any ratio and the composition
is not of fixed proportion. A solution is a
homogeneous mixture of two or more substances. A solute is defined as the
substance that dissolves in a solution. A solvent is defined as
the material that dissolves the other substance(s) in a solution. It is the
dissolving medium. Solubility is defined as
the maximum amount of a substance which will dissolve in a given amount of
solvent at a specific temperature. When the shared pair of
electrons which are forming the bond in a molecule are not shared equally, the
resulting molecule will have a positive end and a negative end. This type of
bond is a polar covalent bond. The molecules are called dipolar or polar
molecules. In general, the fewer
electrons an element must lose, gain, or share to reach a stable shell
structure, the more chemically active the element is. The likelihood of
elements forming compounds is strongly influenced by the valence shell and on
the stability of the resulting molecule. The more stable the molecules are, the
more likely these molecules are to form. Elements combine in specific
ratios, regardless of the type of bond, to form molecules. The three basic laws of
chemical reactions are discussed: The Law of Conservation of
Mass - "In a chemical reaction the total mass of the products equal the
total mass of the reactants." (2) The Law of Definite Proportions - "No matter how a
given chemical compound is prepared, it always contains the same elements in
the same proportions by mass." (3) The Law of Multiple Proportions - "If two elements
combine together to form more than one compound, then the masses of one of
these elements combining with a fixed mass of the other are in a simple ratio
to one another." <%CUT%> This chapter will discuss the method of qualifying
solutions. The balancing of the chemical equations will also be explained in
this chapter. EO 2.7 STATE Le Chatelier's principle. EO 2.8 DEFINE the following terms: a. ppm c. Density b. Molarity d. Normality EO 2.9 BALANCE chemical equations that combine element and/or compounds.
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