THERMOCHEMISTRY
BY LESLIE JASPER
THERMOCHEMISTRY
• Thermochemistry is the study of heat
change in chemical reactions.
System
• A system is the specific part of the
universe that is of interest to us. Studying
the system is important in order to study
changes associated with chemical
reactions.
Types of Systems
• Open system
• Closed system
• Isolated system
Types of Energy Processes
• Exothermic- this process involves the
release of energy during a chemical
reaction.
• Endothermic- this process involves the
intake of energy during a chemical
reaction.
Energy
• Energy is the capacity to do work. Work is
measured as force times the distance.
The term “energy” is a much used term
that represents an abstract concept. All
different types of energy can be converted
from one form to another.
Types of Energy
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Potential Energy
Kinetic Energy
Solar Energy
Geothermal Energy
Nuclear Energy
Tidal Energy
Hydroelectric Energy
Thermodynamics
• Thermodynamics is the scientific study of
the interconversion of heat and other kinds
of energy. In thermodynamics we study
the changes in the state of a system and
properties that determine the state of a
system known as state functions.
Enthalpy
• Enthalpy is a state function and is the
difference between the enthalpies of the
products and the enthalpies of the
reactants.
• H= H (products) – H (reactants)
Specific Heat
• Specific Heat is the amount of heat
required to raise the temperature of one
gram of the substance by one degree
Celsius. Specific heat is an intensive
property while heat capacity is an
extensive property.
Calorimetry
• Calorimetry is the measurement of heat
changes. A calorimeter is a closed
container designed to monitor heat loss or
gain between two substances. Types of
calorimeters include:
• Constant-Volume Calorimeter
• Constant-Pressure Calorimeter
Standard Enthalpy of Formation
• This formation is the heat change that
results when 1 mole of a compound is
formed from its elements at a pressure of
1 atm. Elements are said to be in
standard state at 1 atm. This gives rise to
the term “standard enthalpy”.
Standard Enthalpy of Reaction
• This is the enthalpy of a reaction carried
out at 1 atm.
• aA + bB = cC + dD
Methods to measure standard
enthalpy formation
• Direct method- this method measures the
standard enthalpy of formation when
compounds are readily synthesized from
their elements.
• Indirect method- this method measures
the standard enthalpy of formation when
the reaction is going too slow or side
reactions are producing undesirable side
reactions and not readily synthesized.
Hess’s Law
• Hess’s Law states that when reactants are
converted to products, the change in
enthalpy is the same whether the reaction
takes place in one step or in a series of
steps.
First Law of Thermodynamics
• This law states that energy can be
converted from one form to another, but
cannot be created or destroyed.
Enthalpy of Solution
• Also known as the heat of solution. This is
the heat generated or absorbed when a
certain amount of solute dissolves in a
certain amount of solvent.
• H(soln) = H(soln) – H(components)
Lattice Energy
• Lattice Energy is the energy required to
completely separate one mole of a solid
ionic compound into gaseous ions.
Heat of Dilution
• Heat of Dilution is the heat change
associated with the dilution process. If a
certain solution process is endothermic,
more heat will be absorbed by the solution
from its surroundings. If the process is
exothermic, more heat will be liberated if
more solvent is added to the solution.
Temperature
• Temperature is a relative measure of how
hot or how cold an object is. Temperature
can also be known as a measure of the
concentration of heat. It is a measure of
the average random motion of the unit of
particles (kinetic energy) of an object.
Types of Thermometers
• Thermometers are used to measure
temperature and include:
• Glass mercury-filled thermometers
• Bi-Metallic Stemmed
• Thermisters
• Digital or Thermocouple
• Deep Fry or Candy
• Refrigerator or Oven
• Types of disposable thermometers
• Laser thermometers (new)
Three Major Types of State
Functions
• Entropy (S)
• Gibb’s free energy (G)
• Enthalpy (H).
Entrophy
• Entrophy is the disorder of the universe.
Entropy is constantly increasing in the
universe or at least reaches a maximum at
equilibrium if the system is closed and
unable to exchange heat or mass with its
surroundings.
Gibbs Free Energy
• Gibbs Free Energy is a measure of nonpV work that must go into a reaction to
make it occur (when G is positive) or work
that a reaction can do (when negative). It
can be shown that the change of Gibbs
Free Energy over temperature in a
reaction is the change of the total entropy
of the reacting system plus its
surroundings during a reaction at constant
temperature and pressure.
Thermal Runaway
• Thermal runaway begins when the heat
produced by the reaction exceeds the heat
removed. The surplus of heat raises the
temperature of the reaction mass, which
causes the rate of reaction to increase.
This in turn accelerates the rate of heat
production. This reaction can be
hazardous and/ or cause an explosion. An
example would be sulfuric acid and water.
Calorie
• A calorie is the quantity of heat required to
raise the temperature of one gram of water
one Celsius degree. A calorie is actually
called a kilocalorie. Food producers feel it
is pleasing to the consumer to not hear the
prefix “kilo” in front of calorie.
Clearing up the Myth
• They say that a pregnant woman has to
“eat for two”. This is not true since a
pregnant woman only has to consume 300
more kilocalories than a non-pregnant
woman. This can be accomplished by an
extra serving from each of the five food
groups daily.