By DR T O AKINOLA PRINCIPLES OF CHEMICAL PREPARATIONS FOR COLD THERAPY AND ENDOTHERMIC REACTIONS What is an Endothermic Reaction You might think of chemical reactions as occurring exclusively in laboratories but in reality they occur in the world around us and in our own bodies every day ID: 911898
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Slide1
MODULE: CRYOTHERAPY-LECTURE 2
By
DR T.
O AKINOLA
Slide2PRINCIPLES OF CHEMICAL PREPARATIONS FOR COLD THERAPY AND ENDOTHERMIC REACTIONS
What
is an Endothermic Reaction
You might think of chemical reactions as occurring exclusively in laboratories, but in reality, they occur in the world around us and in our own bodies every day.
Slide3Endothermic
Reactions
Endothermic Reactions:
– Reactions that takes in heat energy from the surroundings
– Temperature of reaction mixture falls. Container feels cold
.
Slide4Example
How many of you have applied a cold pack on your forehead before when you have a severe headache? Or perhaps you are a sportsman/woman that has used cold packs for your joints and muscles before. It certainly helps to relieve the pain isn’t it? But have you ever wondered how it works? It is in fact
Chemistry in actions
!
Slide5Cold pack endothermic
Slide6Chemical Principles
A molecule is the smallest particle in a chemical
element
or
compound
that has the chemical properties of that element or compound. Molecules are made up of
atoms
that are held together by chemical bonds.
Atom + Atom =
MOLECULE
e.g
The molecule-water
,
consists
of two hydrogen atoms and one oxygen atom (H
2
O),
Slide7H2
O
Slide8These
bonds form as a result of the sharing or exchange of
electrons
among atoms. The atoms of certain elements readily bond with other atoms to form molecules. Examples of such elements are oxygen and chlorine.
Slide9The atoms of some elements do not easily bond with other atoms. Examples are neon and argon.
Molecules
can vary greatly in size and
complexity and are always in motion.
Slide10Most
chemical reactions
involve the exchange of energy between molecules and compounds.
The
bonds which hold molecules together contain a tremendous amount of
energy called enthalpy.
Slide11ENTHALPY CHANGE
Energy changes in reactions are caused by the making & breaking of chemical
bonds. In
cryotherapy
, the chemical reaction involves
Bond Breaking
=
Endothermic
Process.
E.g. let us consider hydrogen molecule H-H and Chlorine molecule
Slide12Calculation of Enthalpy change
Given the following constants:
Cl-Cl
bond energy = 242 kJ/
mol
H-H bond energy = 436 kJ/
mol
H-
Cl
bond energy = 431 kJ/
mol
Slide13Slide14H-H +
Cl-Cl
H-
Cl
+
H-
Cl
436 + 242 431 + 431
678 862
∆H=
H
final
-
H
initial
∆
H= 862-678=184kj/
mol
Slide15Since the energy change in the bond breaking is
positive
towards the right of the equation then we say that the chemical reaction is endothermic.
Slide16Some cold packs contain chemicals which takes in heat when they react. This is why cold packs have a cooling effect on their surroundings, i.e. cooling effect on our forehead or our body muscles.
This phenomenon is due to the
reaction
that takes in
heat
, and we call it formally as
Energy Changes
Slide17Ammonium salts such as ammonium nitrate (V) dissolve in water with the absorption of heat. This example of a spontaneous endothermic reaction is the basis of those
commercial
Slide18product you get at pharmacy
e.g
Ice Pack that doesn’t have to be kept in the freezer.
Slide19Instant cold pack
Slide20These ice packs contain a small quantity of ammonium nitrate (NH4NO3) or ammonium chloride (NH4Cl), which is separated from a sample of water by a thin
membrane.
Slide21When the pack is struck with the palm of our hand, the membrane is broken, and the salt dissolves in the water.
Slide22Equation 1
NH4NO3(s
) + H2O(l) –> NH4+(
aq
) + NO3-(
aq
)
Enthalpy Change =
25kj/
mol
Equation 2
NH4Cl(s) + H2O(l) –> NH4+(
aq
) +
Cl
-(
aq
)
Enthalpy Change = 20kj/
mol
Slide23Because the reaction is
Endothermic
(+
ve
Enthalpy change), it absorbs heat from its surroundings, and the ice pack (which is the plastic membrane) can get cold enough to treat minor athletic injuries and headache.
Slide24When these bonds are broken, a large amount of energy is released. This also means that it takes a great deal of energy to form bonds. The total energy of a chemical reaction is determined by the number of bonds broken and formed.
Slide25An
endothermic reaction
occurs when a greater amount of energy is required to break the existing bonds in the reactants than is released when the new bonds form in the products
.
Slide26In other words, this means an endothermic reaction requires or takes in energy in order for it to proceed. This required energy can be provided in many forms, but it is typically in the form of heat.
Slide27Slide28If substance
A
must take energy away from the environment in order to form product D, then the reaction is said to be endothermic, and the victimized environment will feel
colder
after the reaction.
Slide29Examples of endothermic reactions:
Melting
of ice absorbs energy
Dissolving ammonium nitrate in water( the essence of commercial cold packs)
NH
4
NO
3(s)
+
energy
à
NH
4
NO
3(
aq
)
N
2
+ O
2
+
energy
à
NO