Points To Remember
Thermodynamics: Thermodynamic
deals
with the relation of energy changes to physical and chemical changes and with
the transformation of one from of energy into other form.
System: A thermodynamical system
is a part of the universe separated from the surrounding by definite boundaries
in order to study the effect various variables such as temperature, pressure
etc upon the contents.
Surroundings: The protion of matter
outside the systemis known as surroundings.
Boundary: The imaginary surface
separating the system from surrounding is called boundary.
Type Of System
Open System: A system that can
exchange energy and matter with its surroundings.
Closed System: A system that can
exchange only energy with its surroundings.
Isolated System: A system that cannot
exchange either energy or matter with its surroundings.
Homogeneous System: A system which
is completely uniform throughout i.e. consisting only one phases.
Heterogeneous System: A system which
is not uniform throughout i.e. consisting of two or more phases.
Macroscopic System: A large number
of chemical species contained by a system is called macroscopic system. The
properties of the system, which arise from the large number of species, are
called macroscopic properties.
Properties of System
Extensive Properties: The properties
which depend on the quantity of the substance present in the system are called
extensive properties.
Intensive Properties: The properties
which depend on the nature of the substance and not on amount of substance
present in the system are intensive properties.
Thermodynamic Equilibrium:
A system is said to have attained a state of thermodynamical Equilibrium when
it shows no further tendency to change its property with time. Following three
types of equilibrium exist in a system.
Thermal Equilibrium: It involves no
flow of currents of matter within the system or at its boundaries.
Mechanical Equilibrium: It
involves no flow of currents of matter within the system or at its boundaries.
Chemical Equilibrium: If the chemical
composition of a system is not spontaneously changing with time, it is in a
state of chemical equilibrium.
Thermodynamic Process
Isothermal Process: If the
temperature of the system remains constant throughout the process, then it is
known as isothermal process i.e. dT = 0.
Adiabatic Process: If no heat
enters or leaves the system during any step of the process, then it is called
adiabatic process i.e. dq = 0.
Isochoric Process: If the volume
of the system remains constant during each step of the process, then it is
called isochoric process i.e. dv = 0.
Isobaric Process: If the pressure of the
system remains constant during each step of the change in the state of a
system, then it is called isobaric process i.e. dp = 0.
Cyclic Process: A system undergoes a
series of change and ultimately comes back to the initial state is known as
cyclic process i.e. dE = 0, dH = 0.
Work: It is the product of
force applied and the distance moved along the direction of the force.
Pressure- Volume Work: This is a type
of mechanical work performed, when a system changes its volume against an
opposing pressure.
Unit: C.G.S = erg; S.I =
Joule. 1J = 107 ergs = 1Nm = 1kg m2 S+2.
Heat: Unit: C.G.S = Calories; S.I
= Joule.
· W
is +ve, work has been done on the system.
· W
is –ve, work has been done by the system.
· Q
is +ve, heat has been absorbed by the system.
· Q
is –ve, heat has been evolved by the system.
Internal Energy: A definite amount of
energy is associated with the substance. Such energy is called internal energy.
· It
is a state function.
· The
internal energy of a molecule is the sum of translational, rotational,
vibrational, electronic and nuclear energy.
State of a System: A thermodynamic
system is said to be in a certain state when all its properties are fixed.
State Functions: When state of a system
is altered, the change in variable depends on initial and final states of the
system. These variables are referred to as state variables or state functions.
Enthalpy or Heat Content:
It is the amount of heat energy evolved or absorbed in a chemical reaction when
the gram moles of all the substances as given by the chemical equation have
completely reacted.
· Enthalpy
is a state function.
Heat OF Formation: It is the
change of enthalpy, when one gram mole of the substance is formed from its
elements.
Standard Heat of Formation:
It is the heat of formation when all the substances involved in the reaction
are each at unit activity. (i.e. at 25 oC and 1.0 atmosphere
pressure)
First Law of Thermodynamic:
The total energy of an isolated system remains constant.
· Heat
absorbed at constant volume is equal to increase in total energy.
· Heat
absorbed at constant pressure is equal to the increase in heat content or
enthalpy of the system.
Second Law of thermodynamic:
It is impossible to construct a device, which will
work in a complete cycle and convert heat into work without producing any
change in the surroundings.
For any spontaneous process, the change in entropy
of the system plus change in entropy of the surroundings is more than zero.
Entropy:
· Entropy
measures the disorder in a system.
· The
change in entropy is positive if disorder of the system increases and it is
negative if disorder of the system decreases.
· Spontaneous
changes always occur with an increase of entropy of the universe.
· Entropy
of a system as a whole is an irreversible process.
· Entropy
is expressed in cal. Degree-1 and JK-1 (SI unit).
Gibb’s Free Energy:
· Gibb’s
free energy (G) is a criterion for spontaneity.
· If
the change in Gibb’s free energy (ΔG) is negative, the reaction is spontaneous
and feasible.
· If
ΔG is positive, the reaction is impossible.
· If
ΔG = 0, reaction is in equilibrium.
Third Law Of
Thermodynamics: According to it, entropy of all pure
crystalline solids is zero at absolute zero of the temperature.
· Hess’s
Law:
The amount of heat evolved or absorbed in a chemical change is the same whether
the process take place in one or several steps.
· Standard
Heat of Combustion: It is the enthalpy change when one mole
of the substance is completely burned in oxygen.
Heat of Atomization:
It is the enthalpy change when one mole of a substance in its standard state is
completely changed into atom in the gaseous state.
Heat of Hydrogenation:
It is the enthalpy when one mole of an unsaturated compound reacts with
hydrogen and is completely changed into the corresponding saturated compound.
Heat of Neutralization:
The standard enthalpy of neutralization is the amount of heat evolved when one
mole of hydrogen ions from an acid react with one mole of hydroxide ions from a
base to from one mole of water.
Born- Haber Cycle:
· This
is the special application of Hess’s law to binary ionic compounds.
· It
enables us to calculate their lattice energies.
Lattice Energy:
The lattice energy of an ionic crystal is the enthalpy of formation of one mole
of the ionic compound from gaseous ions under standard conditions.
· Lattice
energies cannot be determined directly but values can be obtained indirectly by
means of an energy cycle.
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