observing chemical kinetics for numerous reactions types
Integrated Rate Law
Units of Rate Constant
Linear Plot to Determine
Constant to the Slope of
1. Define Reaction Rate
2. TRUE or FALSE: Changes in the temperature or the introduction of a
catalyst will affect the rate constant of a reaction
For sample problems 3-6, use Formula 6 to answer the questions
3. For the given reaction above, state the rate law.
4. State the overall order of the reaction.
5. Find the rate, given k = 1.14 x 10
O] = 2.04M
6. Find the half-life of the reaction.
disappearance of reactants or the change in concentration of the appearance of
products per unit time.
2. FALSE. The rate constant is not dependant on the presence of a catalyst.
Catalysts, however, can effect the total rate of a reaction.
3. Rate= k[H
O] Rate= k[H
5. 2.33 x 10
6. 29.7 s
3.3. A chemical equation is the symbolic representation of a chemical reaction
in the form of symbols and formulae, wherein the reactant entities are given on the
left-hand side and the product entities on the right-hand side.
to the symbols and formulae of entities are the absolute values of the stoichiometric
numbers. The first chemical equation was diagrammed by Jean Beguin in 1615.
A chemical equation consists of the chemical formulas of the reactants (the
starting substances) and the chemical formula of the products (substances formed in
the chemical reaction). The two are separated by an arrow symbol (
, usually read
as "yields") and each individual substance's chemical formula is separated from
others by a plus sign.
As an example, the equation for the reaction of hydrochloric acid with sodium
can be denoted:
2 HCl +2 Na
→2 NaCl + H 2
This equation would be read as "two HCl plus two Na yields two NaCl and H
two." But, for equations involving complex chemicals, rather than reading the letter
and its subscript, the chemical formulas are read using IUPAC nomenclature. Using
IUPAC nomenclature, this equation would be read as "hydrochloric acid plus sodium
yields sodium chloride andhydrogen gas."
This equation indicates that sodium and HCl react to form NaCl and H
. It also
molecules and the reaction will form two sodium chloride molecules and one
diatomic molecule of hydrogen gas molecule for every two hydrochloric acid and two
sodium molecules that react. Thestoichiometric coefficients (the numbers in front of
the chemical formulas) result from the law of conservation of mass and the law of
conservation of charge
Chemical reactions happen all around us: when we light aMATCH , start a
car, eat dinner, or walk the dog. A chemical reaction is the process by which
substances bond together (or break bonds) and, in doing so, either release or consume
energy (see our Chemical Reactions module). A chemical equation is shorthand that
scientists use to describe a chemical reaction. Let's take the reaction of hydrogen with
oxygen to form water as an example. If we had a container of hydrogen gas and
burned this in the presence of oxygen, the two gases would react together, releasing
energy, to form water. To write the chemical equation for this reaction, we would
place the substances reacting (the reactants) on the left side of an equation with an
arrow pointing to the substances being formed on the right side of the equation (the
products). Given this information, one might guess that the equation for this reaction
The plus sign on the left side of the equation means that hydrogen (H) and
oxygen (O) are reacting. Unfortunately, there are two problems with this chemical
equation. First, because atoms like to have full valence shells, single H or O atoms
are rare. In nature, both hydrogen and oxygen are found asdiatomic molecules, H
, respectively (in forming diatomic molecules the atoms shareelectrons and
oxygen gas consists of O
. Correcting our equation we get:
But we still have one problem. As written, this equation tells us that one
hydrogen molecule (with two H atoms) reacts with one oxygen molecule (two O
atoms) to form one water molecule (with two Hatoms and one O atom). In other
words, we seem to have lost one O atom along the way! To write a chemical equation
correctly, the number of atoms on the left side of a chemical equation has to be
precisely balanced with the atoms on the right side of the equation. How does this
happen? In actuality, the O atom that we "lost" reacts with a second molecule of
hydrogen to form a second molecule of water. During the reaction, the H-H and O-O
bonds break and H-O bonds form in the water molecules, as seen in the simulation
Interactive Animation:The formation of water
The balanced equation is therefore written:
In writing chemical equations, the number in front of the molecule's symbol
If no coefficient appears in front of a molecule, we interpret this as meaning one.
In order to write a correct chemical equation, we must balance all of the atoms
on the left side of thereaction with the atoms on the right side. Let's look at another
example. If you use a gas stove to cook your dinner, chances are that your stove
burns natural gas, which is primarily methane. Methane (CH
) is a molecule that
you are supplying the activation energy to start the reaction of methane with oxygen
in the air. During this reaction, chemical bonds break and re-form and the products
that are produced are carbon dioxide and water vapor (and, of course, light and heat
that you see as the flame). The unbalanced chemical equation would be written:
(carbon dioxide) + H
Look at the reaction atom by atom. On the left side of the equation we find one
carbon atom, and one on the right.
Next we move to hydrogen: There are four hydrogen atoms on the left side of
the equation, but only two on the right.
Therefore, we must balance the H atoms by adding the coefficient "2" in front
of the water molecule(you can only change coefficients in a chemical equation, not
subscripts). Adding this coefficient we get:
What this equation now says is that two molecules of water are produced for
every one molecule of methane consumed. Moving on to the oxygen atoms, we find
two on the left side of the equation, but a total of four on the right side (two from the
molecule and one from each of two water molecules H
the oxygen molecule on the left side of the equation, showing that two oxygen
molecules are consumed for every one methane molecule that burns.
Dalton's law of definite proportions holds true for all chemical reactions (see
our Early Ideas about Matter: From Democritus to Dalton module). In essence, this
law states that a chemical reactionalways proceeds according to the ratio defined by
the balanced chemical equation. Thus, you can interpret the balanced methane
equation above as reading, "one part methane reacts with two parts oxygen to
produce one part carbon dioxide and two parts water." This ratio always remains the
same. For example, if we start with two parts methane, then we will consume four
and generate two parts CO
and four parts H
O. If we start with excess of
the excess reactant will not be consumed:
→ C O
In the example seen above, 3O
had to be added to the right side of the
reaction. In this example, methane is called the limiting reactant.
Although we have discussed balancing equations in terms of numbers of atoms
and molecules, keep in mind that we never talk about a single atom (or molecule)
when we use chemical equations. This is because single atoms (and molecules) are so
tiny that they are difficult to isolate. Chemical equations are discussed in relation to
the number of moles of reactants and products used or produced (see our The Mole
module). Because the mole refers to a standard number of atoms (or molecules), the
term can simply be substituted into chemical equations. Thus, the balanced methane
equation above can also be interpreted as reading, "one mole of methane reacts with
two moles of oxygen to produce one mole of carbon dioxide and two moles of
The Lewis definition is the most general theory, having no requirements for
Lewis Acids and Bases
An acid is a substance that accepts a lone pair of electrons.
A base is a substance that donates a lone pair electrons.
and base have bonded by sharing the electron pair. Lewis acid/base reactions are
different from redox reactions because there is no change in oxidation state.
This reaction shows a Lewis base (NH
) donating an electron pair to a Lewis
) to form an adduct (NH
Substances capable of acting as either an acid or a base are amphoteric. Water
is the most important amphoteric substance. It can ionize into hydroxide (OH
, an acid). By doing so, water is
Donating or accepting a proton (Brønsted-Lowry), and
Accepting or donating an electron pair (Lewis).
Important A bare proton (H
thehydronium ion (H
). Although many
equations and definitions may refer to the
"concentration of H
ions", that is a misleading
) ions. Fortunately, the
number of hydronium ions formed is exactly
equal to the number of hydrogen ions, so the two
can be used interchangeably.
ions actually exist as hydronium, H
Water will dissociate very slightly (which further explains its amphoteric
The presence of hydrogen ions
of hydroxide ions indicates a base.
Being neutral, water dissociates into
This equation is more accurate—
because they bond to form hydronium.
Although the other halogens make strong acids, hydrofluoric acid (HF) is a
weak acid. Despite being weak, it is incredibly corrosive—hydrofluoric acid
dissolves glass and metal!
Most acids and bases are weak. You should be familiar with the most common
strong acids and assume that any other acids are weak.
HCl, HBr, HI Hydrohalic acids
Within a series of oxyacids, the ions with the greatest number of oxygen
molecules are the strongest. For example, nitric acid (HNO
) is strong, but nitrous
) is weak. Perchloric acid (HClO
) is stronger than chloric acid (HClO
). Hypochlorous acid (HClO) is
Common strong bases are the hydroxides of Group 1 and most Group 2 metals.
For example, potassium hydroxide and calcium hydroxide are some of the strongest
bases. You can assume that any other bases (including ammonia and ammonium
hydroxide) are weak.
Formula Strong Base
Acids and bases that are strong are not necessarily concentrated, and weak
ability of a substance to dissociate. Furthermore, polyprotic acids are not
necessarily stronger than monoprotic acids.
Properties of Acids and Bases
Now that you are aware of the acid-base theories, you can learn about the
physical and chemical properties of acids and bases. Acids and bases have very
different properties, allowing them to be distinguished by observation.
Bromothymol blue is an indicator that turns blue in a base, or yellow in acid.
indicators will change color in the presence of an acid or base. A common indicator is
litmus paper. Litmus paper turns red in acidic conditions and blue in basic conditions.
Phenolphthalein purple is colorless in acidic and neutral solutions, but it turns purple
once the solution becomes basic. It is useful when attempting to neutralize an acidic
solution; once the indicator turns purple, enough base has been added.
A less informative method is to test for conductivity. Acids and bases in
Therefore, acids and bases are electrolytes. Strong acids and bases will be strong
electrolytes. Weak acids and bases will be weak electrolytes. This affects the amount
However, acids will react with metal, so testing conductivity may not be
The physical properties of acids and bases are opposites.
These properties are very general; they may not be true for every single acid or
immediately and properly (according to the procedures of the lab you are working
in). If, for example, sodium hydroxide is spilled, the water will begin to evaporate.
Sodium hydroxide does not evaporate, so the concentration of the base steadily
increases until it becomes damaging to its surrounding surfaces.
Acids will react with bases to form a salt and water. This is a neutralization
reaction. The products of a neutralization reaction are much less acidic or basic than
the reactants were. For example, sodium hydroxide (a base) is added to hydrochloric
Acids react with metal to
carbonates to produce water, CO
Acids react with metal oxides
Bases are typically less reactive and violent than acids. They do still undergo
many chemical reactions, especially with organic compounds. A common reactions is
saponificiation: the reaction of a base with fat or oil to create soap.