Download Medical Chemistry Lecture By : Asst. Lect. Tariq Al Mgheer College

Medical Chemistry Lecture By : Asst. Lect. Tariq Al Mgheer
College of Medicine- Babylon University
Matter And Energy
Matter define as anything that has mass and occupies space.
PROPERTIES OF MATTER
A particular kind of matter, such as water, gold, silver, salt, or sugar, is called a
substance. Every substance has a characteristic set of properties that makes it different
from all other substances. These properties give it a unique identity. For example, sugar
is an odorless, white solid that has a sweet taste. When heated, sugar melts and turns
brown. The properties of a substance that are characteristic of that substance are called
its intrinsic properties. The^e properties do ,".ot depend on the size or shape of the
substance.
Some intrinsic properties are more uSefU ihan others in describing matter, such as
melting, boiling points and densities. They are easily measured and expressed in
numbers, it is give numerical values. For example th© specific pi-operties of water are
its boiling point (100° C), melting point (0° C), and density (1.0 g/rnL at 4°C). No other
substance has exactly this set of properties These intrinsic properties are called
physical properties.
Many substances react, either alone or with other matter, to form new materials.
These reactions are called tne chemical prop srties of a substance. CLSSIFYING
MATTER
Matter is ciassified as either a mixture or a pure substance. A mixture contains a
number of different substances mixed together. A mixture has no unique set of
properties. Rather, it has the properties of a!! the substances that are a part of it.
A mixture is either heterogeneous or homogeneous. The parts of a
heterogeneous mixture ;re visibly different, and the parts of a homogeneous mixture
cannot be detected even with a microscope.
A mi/ture can be separated into its parts by using the differences in the physical
properties of the parts. For exampic, when the temperature of air is lowered, water
vapor separates as liquid (rain) or solid water (snow). When the air is cooled still further
solid carbon dioxide (dry ice) form. Finally, ^ oven lower temperatures, the rest of the air
becomes liquid. Thus, the differences in the physical properties of the substances in the
mixture allow us to separate them
Pure substances are classified as either elements or compounds. COMPOSITION OF
MATTER
Atoms are ^:» fundamental units of l.llerrlerlts. An element is a substance that contains
only one kind of atom. Today, there are only 106 elements.
Medical Chemistry Lecture By : Asst. Lect.Tariq Al mgheer- College of
Medicine- Babylon University
Atoms combine to form molecules. A substance that contains only one kind of
molecule is called a pure compound. A molecule is the smallest particle that has
the properties of a pure compound. STATES OF MATTER
All the elements and most simple compounds can exist as a gas, liquid, or,
sold. These are the three states of matter. Water is a familiar example of a
compound that exists in the three states. Liquid water is the most common form.
Yet when the temperature is lowered, water freezes to form ice, the solid form of
water. When water evaporates or is heated to its boiling point, it exists as water
vapor, the gaseous form of water.
Not all substances can exist in three states. Many large and complex molecules
exist only in the solid or liquid state because they are unstable when heated to their
melting or boiling point. For example, sugar decomposes instead of melting when
heated.
A plasma is typically an ionized gas, and is usually considered to be a distinct
phase of matter (the fourth state of matter) in contrast to solids, liquids, and gases
because of its unique properties. Chemist and physicist use the name plasma to
describe this region containing balanced charges of ions and electrons.
PHYSICAL AND CHEMICAL CHANGES
Everything in the world undergoes change. These changes can be classified as
either physical or chemical. Chemical changes result in the disappearance of one
or more substances and the formation of new ones.
Chemical changes are usually called chemical reaction.
No new substances are formed in a physical change However, a physical
change often results in the change of some intrinsic properties. For example, the
density of ice is 0.917 g/mL, which is different from that of liquid water.
During chemical reactions and physical changes, energy is either released or
absorbed. We get the energy we need for our world from chemical reactions. Our
bodies get the energy they need from the food we eat. But what is energy?
ENERGY AND ITS TRANSFER
The word energy is used to denote activity. We also speak of the energy that
can be obtained from petroleum. But we cannot see, taste, or smell energy. Unlike
matter, energy does not occupy space; yet we can feel its effects. Energy is not a
thing but is more like a characteristic of a substance.
All m&iter has energy. This energy has many forms. potential, kinetic, chemical,
atomic, and radiant energy are common types. An object has potential energy
because Medical Chemistry Lecture By : Asst. Lect. Tariq Al Mgheer College of Medicine- Babylon
University
of its position. For example, water at the top of a waterfall has potential energy as a
result of its position above the surface of the earth. An object has kinetic energy as a
result of its motion. A moving car and an airplane in flight all have kinetic energy.
Chemical energy is the energy stored in the molecule as a result of the kinds and
positions of its atoms. Atomic or nuclear energy is associated with the structure of
atoms. Radiant energy is the energy of light.
The energy of any object changes whenever it undergoes a chemical reaction or
physical change. This energy change occurs by transferring energy. For example, part
of the energy of wood is transferred to the surrounding air when it is burned. The energy
is transferred by several methods. Four of the most common are work, heat, sound,
and light These are all visible signs of a transfer of energy.
It is important to realize that, although a substance may contain energy, it never
contains heat or work. Heat and work are evident only when the energy of the material
changes and a transfer of energy occur. The terms heat content and work content of
substances are often used. These terms mean that the change in energy of a substance
will occur in the form of heat or work.
Chemical reactions involved in our body also demonstrate the transfer of energy.
The food we eat provides the energy that allows our bodies to carry out the normal work
of contraction and motion Food also provides us with heat to maintain a constant body
temperature. Food undergoes a series of chemical reactions in our bodies that result in
the transfer of part of the chemical energy to muscles to do work and to the
surroundings as heat.
UNITS OF ENERGY
Heat is one of the most easily measured forms of energy. The most common unit of
measurement of heat is the calorie. Its symbol is cal. A calorie is defined as the amount
of heat needed to raise the temperature of 1 g of water from 14.5° to 15.5° C. Although
is the exact definition of a calorie, approximately 1 calorie is needed to raise the
temperature of 1 g of water by 1° C at any temperature between 0 and 70° C. Most
chemical reactions release several thousand calories; as a result, quantities of heat are
usually reported as kilocalones (1 kcal = 1000 cal). The Sl unit of energy is the joule. Its
symbol is J There are exacdy 4.184 J in 1 cal. Be careful in using the calorie as a unit,
because there are actually two calories in use:
the one defined above, and the Calorie (with a capital C), used in nutrition. One
Calorie is equal to 1 kcal.
EXARCISE: How much heat, in cai and kcal, is needed to raise the temperature of 1000
Medical Chemistry Lecture By : Asst. Lect. Tariq Al MgheerCollege of Medicine- Babylon University
g of water from 1°to250 C?
1 calorie is needed to raise the temperature of 1 g of water
1000 g X 1 calone/1 g = 1000 cal or 1 kcal 1 kcal X24=
24kcal = 24000 cal THE BODY AND HEAT TRANSFER
The human body at rest gets its energy by means of a series of complex chemical
reactions called metabolism. The body gets its heat from a part of this energy. The
temperature of the body must stay fairly constant to function properly. Either too much
or too little heat can be lethal. The body gets rid of excess heat by transferring it to the
surroundings in a number of ways.
Evaporation of water from the skin is one way the body loses heat. This process
takes advantage of the fact that heat is needed to transform liquid water into its vapor.
The heat needed to carry out this physical change is called the heat of vaporization It
is defined as the number of calories needed to change 1 g of substance from the liquid
to the vapor state at its normal boiling point. The heats of vaporization of a number of
compounds used in medicine are given in Table 1.
Table 1 Heats of Vaporization of Various Compounds
Compounds
Hear of Vaporization Compound (cal /g)
Water
540
IsopropyI alcohol
159
Diethyl ether
84
Ethyl chloride
93
Chloroform
59
Ethyl alcohol
204
Notice that the heat of vaporization of water is higher than that of the other
compounds. This means that it takes more heat to vaporize 1g of water than 1g
OT
most
other compounds.
The body also transfers hear to its surroundings by radiation The body is like a hot
water radiator used in cars. Both give off heat. The heat radiated from the body
accounts for much of its heat loss, particularly during cold weather. Much heat is lost
from an uncovered head. This loss can be greatly reduced simply by wearing a hat.
Heat is transferred from one substance to another substance that is colder. This
is called heat conduction This is another way that heat can be transferred to' or from
the body. For example, when an ice pack is placed on the skin, heat is transferred from
the skin to the ice and the skin becomes cool.
Medical Chemistry Lecture By : Asst. Lect. Tariq Al MgheerCollege of Medicine- Babylon University
Water is the most abundant compound in the body. Body water can act internally to
control body temperature because it can absorb a fairly large amount of heat with
relatively little change in temperature. The amount of heat needed to raise the
temperature of 1 g of a substance by 1° Celsius is called its specilic heat. Water has a
higher specific heat than most compounds (1 cal/g X °C). Forexample, it takes 10 times
as much heat to raise the temperature of a quantity of water by 1° than it does to
increase the temperature of the same amount of copper by 1 ° (0.0949 cal / g X °C).
This means that water in the body can absorb a fairly large amount of heat without
changing temperature. In this way, water acts as an internal temperature regulator.