2. CONTENTS :
Definition
History
Measurement
Certain laws to be followed while writing thermo
chemical equations
Thermo chemistry in daily life
Importance of thermo chemistry
3. DEFINITION :
•Branch of chemistry which deals with the quantity of heat evolved or
absorbed during a chemical reaction.
•In other words, study of energy or heat in chemical reaction and/or
physical transformation.
•It also helps in determining whether reaction is spontaneous or non-
spontaneous.
•It coalesces the concepts of thermodynamics with concept of energy in
forms of chemical bonds
Commonly includes calculations of -:
1. Heat capacity
2. Enthalpy
3. Entropy
4. Free energy
5. Calories
6. Heat of Combustion
7. Heat of formation
4. HISTORY :
• Thermochemistry rests on two generalizations-:
1. Lavoisier and Laplace’s law (1780): The energy change in any
transformation is equal and opposite to energy change in the reverse
process.
2. Hess' law (1840): The energy change in any transformation is the same
whether the process occurs in one step or many.
These statement helps in formulation of first law of thermodynamics in
1845.
In 1858, Gustav Kirchhoff gave the variation of the heat of reaction given
by formula :
dH/dT ΔCp
Integration of this equation gives value of heat of reaction from one value
of temperature to another value of temperature.
5. MEASUREMENT :
Calorimeter-:
1. Is a enclosed chamber used for heat
measurement in which change examine
occurs.
2. Temperature is maintained using
thermocouple and thermometer.
3. Temperature v/s time graph is plotted to
calculate fundamentals units like heat
change, heat of formation or combustion
etc.
First ice calorimeter
used in winter (1782-
1783).
Differential Scanning
Calorimeter
6. CERTAIN LAWS TO BE FOLLOWED :
ΔH is directly proportional to the quantity of a substance
that reacts or is produced by a reaction.
ΔH for a reaction is equal in magnitude but opposite in
sign to ΔH for the reverse reaction.
ΔH is independent of the number of steps involved.This
rule is called Hess's Law. It states that ΔH for a reaction is
the same whether it occurs in one step or in a series of
steps. Another way to look at it is to remember that ΔH is a
state property, so it must be independent of the path of a
reaction.
If Reaction (1) + Reaction (2) = Reaction (3), then ΔH3 =
ΔH1 + ΔH2
7. THERMOCHEMISTRY IN DAILY LIFE:
All types of vehicles that we use, cars, motorcycles, trucks,
ships, aeroplanes, and many other types work on the basis of
second law of thermodynamics and Carnot Cycle. They may
be using petrol engine or diesel engine, but the law remains
the same.
All the refrigerators, deep freezers, industrial refrigeration
systems, all types of air-conditioning systems,heat pumps, etc
work on the basis of the second law of thermodynamics.
All types of air and gas compressors, blowers, fans, run on
various thermodynamic cycles.
8. One of the important fields of thermodynamics is heat transfer,
which relates to transfer of heat between two media. There are
three modes of heat transfer: conduction, convection and
radiation. The concept of heat transfer is used in wide range of
devices like heat exchangers, evaporators, condensers,
radiators, coolers, heaters, etc.
Thermodynamics also involves study of various types of power
plants like thermal power plants, nuclear power plants,
hydroelectric power plants, power plants based on renewable
energy sources like solar, wind,geothermal, tides, water waves
etc,
Renewable energy is an important subject area of
thermodynamics that involves studying the feasibility of using
different types of renewable energy sources for domestic and
commercial use.
9. IMPORTANCE OF THERMOCHEMISTRY
Thermochemistry is a very important field of study
because it helps to determine if a particular reaction
will occur and if it will release or absorb energy as it
occurs.
It is also possible to calculate how much energy a
reaction will release or absorb and this information
can be used to determine if it is economically viable
to use a particular chemical process.
Thermochemistry, however, does not predict how
fast a reaction will occur.
