Unformatted text preview: Thermodynamics NARAYAN TUTORIALS IITian Sushil Kumar The branch of science which deals with study of different forms of energy and their interconversion is called
A system in thermodynamics refers to that part of universe in which observations are made.
The remaining portion of universe which is not part of system constitutes the surroundings. The surroundings
include everything other than the system.
The wall (real or imaginary) that separates the system from the surroundings is called boundary.
Types of system
Exchange of energy
Exchange of matter
The state of a thermodynamic system is described by its measurable or macroscopic (bulk) properties. The
state of the surroundings can never be completely specified.
State variables are the measurable properties of system required to describe the state of the system.
Examples are temperature, pressure, volume etc.
Various types of processes:Type of process
Isothermal ( T = 0)
Process in which temperature of system
Adiabatic ( Q= 0)
Process in which there is no transfer of
heat between the system and surroundings
Isobaric ( P= 0)
Process in which pressure of system remains
Isochoric( V= 0)
Process in which volume of system remains
Work done by the system
W = positive
Work done on the system
W = negative
Heat transferred From surroundings to the system
Q = positive
Heat transferred From system to the surroundings
Q = negative
First law of Thermodynamics:First law of thermodynamics is also called as law of conservation of energy i.e. energy can neither be created
nor destroyed. It also states that the energy of an isolated system is constant.
Q = U+ W
Expression of Work:
W= P(V2±V1) = nR(T2±T1)
W = nRT ln(V2/V1) = 2.303nRT log(V2/V1)
W = (P1V1-P2V2)/( ± 1) = (nRT1-nRT2)/( ± 1)
Reversible and Irreversible process:- A process or change is said to be reversible, if a change is brought out
in such a way that the process could, at any moment, be reversed by an infinitesimal change. A reversible
process proceeds infinitely slowly by a series of equilibrium states such that system and the surroundings are
always in near equilibrium with each other. Processes other than reversible processes are known as irreversible
Free Expansion:- Expansion of a gas in vacuum (Pex= 0) is called free expansion. No work is done during
free expansion of an ideal gas whether the process is reversible or irreversible.
Enthalpy:- The enthalpy of a system may be defined as the sum of the internal energy and the product of its
pressure and volume. It is denoted by the symbol H and is given by H = U + PV.
H= U+P V
NARAYAN TUTORIALS Page 1 Thermodynamics NARAYAN TUTORIALS IITian Sushil Kumar Types of reaction:Type of reaction
Reactions in which heat is evolved during the reaction
Reactions in which heat is absorbed during the reaction
Extensive and Intensive property:
An extensive property is a property whose value depends on the quantity or size of matter present in the
system. Examples are mass, volume, internal energy, enthalpy, heat capacity, etc.
An intensive property is a property whose value does not depend on the quantity or size of matter present in
the system. Examples are temperature, density, pressure etc.
Specific heat capacity:
Specific heat, also called specific heat capacity is the quantity of heat required to raise the temperature of one
unit mass of a substance by one degree Celsius (or one Kelvin).
Q = m x S x T;
At constant pressure, QP = nCP T = H;
At constant volume QV = nCV T = U
For ideal gas: CP ± CV = R
Calorimetry: -Calorimetry is an experimental technique that helps determining energy changes associated
with chemical or physical processes.
Reaction enthalpy: - The enthalpy change accompanying a reaction is called the reaction enthalpy ( rH).
rH = (sum of enthalpies of products) - (sum of enthalpies of reactants)
The standard enthalpy of reaction is the enthalpy change for a reaction when all the participating substances
are in their standard states. The standard state of a substance at a specified temperature is its pure form at
pressure of 1 bar. It is denoted by ( rH ).
Thermochemical equation: - A balanced chemical equation together with the value of its rH is called a
Hess¶s Law of Constant Heat Summation: If a reaction takes place in several steps then its standard reaction
enthalpy is the sum of the standard enthalpies of the intermediate reactions into which the overall reaction may
be divided at the same temperature. rH A rH B = rH1 + rH2 + rH3 rH1
rH3 C rH2 D Different types of Enthalpy:
Type of enthalpy
Standard Enthalpy of fusion
or Molar enthalpy of fusion
Standard Enthalpy of vaporization or
Standard Enthalpy of sublimation Enthalpy of formation or Standard
NARAYAN TUTORIALS Definition
The enthalpy change that accompanies melting of one
mole of a solid substance in standard state
The enthalpy change that accompanies vaporizing of
one mole of a liquid at constant temperature and under
standard pressure (1bar)
The enthalpy change when one mole of a solid
substance sublimes at a constant temperature and under
standard pressure (1bar).
The enthalpy change for the formation of one mole of a Symbol
VapH subH fH Page 2 Thermodynamics NARAYAN TUTORIALS molar enthalpy of formation compound from its elements in their most stable states
Enthalpy change when 1 mole of substance is
completely burnt in excess of oxygen or air.
Enthalpy change in breaking one mole of bonds of a
substance completely into atoms in gaseous state.
Amount of energy required to break one mole of bond
of a particular type between atoms in gaseous state
Enthalpy of solution of a substance is
the enthalpy change when one mole of substance
dissolves in a specified amount of solvent. solH =
latticeH + hydH
Enthalpy change which occurs when one mole of an
ionic compound dissociates into its ions in gaseous
Enthalpy change when one gram equivalent of an acid
is completely neutralized by one gram equivalent of a
H2O(l) ; H=-13.7kcal Enthalpy of combustion
Enthalpy of atomisation
Bond dissociation enthalpy
Enthalpy of solution Lattice enthalpy Enthalpy of Neutralisation IITian Sushil Kumar cH
solH latticeH neuH Born-Haber Cycle is used to determine lattice enthalpy of ionic compounds since they cannot be determined
by experiment directly.
Spontaneous and non-spontaneous process: A process that has natural tendency of occurrence in a
particular direction and is reversible only by application of some external agency is known as spontaneous
The processes which are forbidden and are made to take place only by supplying energy continuously from
outside the system are called non-spontaneous process.
Entropy: - Entropy (S) is the measure of randomness of a system. It is a state function. Entropy increases from
solid to gas. Entropy is maximum for gases as they have maximum disorder.
According to Second law of thermodynamics, entropy of the universe always increases during a spontaneous
For reversible process entropy change is given by:
S = ( Qrev)/ T ;
Qrev = is heat absorbed or released during the reaction
and T is the temperature of the reaction
At constant pressure Qrev = H; S = ( H)/T
For spontaneous process Stotal = S system + Ssurr > 0
Gibbs energy: - Gibbs function or Gibbs energy is denoted by G.
G=H-TS ; G = H - T S
The criteria for spontaneous reaction in relation to G at constant pressure and constant temperature is
If G < 0, process is spontaneous
If G = 0, process is in equilibrium
If G > 0, process is non-spontaneous.
Relation between Gibbs energy change G0and equilibrium constant (K):G0 = -2.303RT logK NARAYAN TUTORIALS Page 3 Thermodynamics NARAYAN TUTORIALS Effect of temperature on Spontaneity of Reactions:
- (at low T)
+ (at high T)
+ (at low T)
- (at high T)
+ (at all T) NARAYAN TUTORIALS IITian Sushil Kumar Description
Reaction spontaneous at all temperature
Reaction spontaneous at low temperature
Reaction nonspontaneous at high temperature
Reaction nonspontaneous at low temperature
Reaction spontaneous at high temperature
Reaction nonspontaneous at all temperatures Page 4 ...
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- Spring '11
- Thermodynamics, SUSHIL KUMAR, NARAYAN TUTORIALS