Chapter 1
Thermochemistry


Thermochemistry is the study of “energy
changes” taking place during chemical
reactions and physical processes
reactions.\
This field of science focuses on the energy
changes taking place during chemical
reactions and physical processes
reactions and interaction of the system
and surrounding.
System and Surrounding
 System – the part where we focus our
study

Surrounding – everything that surrounds
the system

Example : in chemical reaction, the
system is the reactants and the container
and everything beyond is surrounding.

Kinds of system
Open system – there are exchange of matter
and energy
Closed system –there are energy exchange
but no matter exchange
Isolated system- there is no exchange of
matter and energy
Types of Energy Transfer
Exothermic process energy is transfer from
the system to surroundings
Burning of wood
Endothermic process energy is transfer from
the surroundings to the system
Ice melting
Heat and Temperature
Heat

is a form of Energy. It transfers between a
system and its surroundings because of a
difference in temperature between them.

Natural flow of heat is from a region of
higher temperature to region of lower
temperature until two regions reach the
same temperature or equilibrium.

However if the flow of heat is from region
of lower temperature to the region of
higher temperature, work is applied.
Titration – of NaCl and HCl

System ______

Surrounding ________
Types of Exchange
Exchange occurs between the interaction of
system and surroundings
Energy exchange- heat, friction, work and etc

Boiling of water
Matter exchange- movement of molecules
across the boundary of the system and the
surroundings

Oxidation of iron (rust)
Temperature

Is a measure of average kinetic energies
of atoms and molecules of a substance

It indicates the direction of the flow of
heat.

The transfer of kinetic energy stops when
a system and its surroundings are at the
same temperature
Energy
 Calories- unit of energy changes is
defined as the energy needed to raise the
temperature of 1.00 g of water to 1 degree
Celsius (from 14.5 oC to 15.5 oC )
Thermodynamics helps us understand the
stability of structure of biomolecules
Spontaneous and Non-spontaneous
1 Calorie = 4.184 joule ( The SI unit of
energy change)
Spontaneous reaction

1 joule = 1 kg*m2/s2
Under suitable conditions, they proceed on
their own.

Note: since joule (J) is a small unit, energy
associated with chemical reactions are
often expressed as Kilojoule (KJ)

Introduction to Thermodynamics
if it occurs by itself without outside assistance
Non-spontaneous reaction
Not all reactions are spontaneous like
decomposition of water.
2 H2O(I)
Thermo means heat and dynamics which
means patterns of change.
Concerned with the study of energy changes
and the flow of energy from one body to
another
It also helps us to determine theoretically
whether a particular chemical reaction will
occur under a given set of conditions
Conversion of energy
Potential energy >kinetic energy> Light energy
(sparks) > sound energy (bang) > chemical
energy (as the brick breaks)
Thermodynamics can help us study how
energy is converted to one from to another.
Stability of molecules and direction of change
Protein folding
Proteins are polymer of amino acids that are
link by polypeptide bonds. This kind of
polymers folds are lower temperature.
Therefore, the structure of protein will change if
you change the conditions the polymers.
2 H2(g) + O2(g)
Water will decompose only by passing an
electric current through it. The reaction will
continue as long as the electric current is
maintained. This type of chemical reaction is
called non-spontaneous.
Thermodynamics processess
 Reversible – is one which can be taken
from its initial state to another state, and
then back to initial state without any
change to either the system or the
surroundings


Ideal and theoretical
Irreversible – if process cannot be
reversed

a spontaneous reaction

More natural

Entropy Increases
THERMODYNAMICS
First Law of thermodynamics
Energy can neither be created nor destroy but
only converted from one form to another
Chemical Reactions
 Internal Energy (U)
It’s a sum of microscopic kinetic
energy and microscopic potential energy
of a system
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Enthalpy Changes
Temperature
(kinetic theory) measures only the
kinetic energy
ENERGY CHANGE IS CAUSED BY ;
HEAT EXCHANGE
WORK DONE BY THE SYSTEM
AND ON THE SYSTEM
How to calculate for the Energy Change of
Internal Energy of a System?
Д U system = q (heat) + W (work)
HEAT EXCHANGE
 (+) q – endothermic process

(-) q – exothermic process
WORK DONE ON or BY the SYSTEM

(-) W- work done by the system

(+) W – work done on the system
If the Energy of the system (Д U system)
change, the Energy of the Surrounding (Д U
surrounding) also changes.