Thermodynamics Thermodynamics

What is thermodynamicsWhat is thermodynamics? ? Thermodynamics is that branch of science that Thermodynamics is that branch of science that

deals with the quantitative relationship deals with the quantitative relationship between heat and other forms of energy.between heat and other forms of energy.

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Some basic terms of Some basic terms of thermodynamicsthermodynamics

System :- a specified part of System :- a specified part of the universe that is under the universe that is under observation.observation.

Surroundings:- the part other Surroundings:- the part other than the system is known as the than the system is known as the surroundings.surroundings.

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Types of systemsTypes of systems Open system :- the system that can Open system :- the system that can

exchange matter as well as energy exchange matter as well as energy with the surroundings.with the surroundings.

Closed system:- the system which Closed system:- the system which cannot exchange matter but can cannot exchange matter but can exchange energy with the exchange energy with the surroundings.surroundings.

Isolated system:- the system which Isolated system:- the system which cannot exchange matter as well as cannot exchange matter as well as energy is called an isolated system.energy is called an isolated system.

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Macroscopic and microscopic Macroscopic and microscopic propertiesproperties

Macroscopic propertiesMacroscopic properties are those are those properties which arise from the properties which arise from the bulk behaviour of matter. Eg:- bulk behaviour of matter. Eg:- temperature , viscosity.temperature , viscosity.

Microscopic propertiesMicroscopic properties are those are those properties which arise from the properties which arise from the microscopic particles of the microscopic particles of the system .Eg:- intermolecular system .Eg:- intermolecular forces.forces.

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Intensive and extensive Intensive and extensive propertiesproperties

Intensive properties are those Intensive properties are those properties whose value is properties whose value is independent upon the amount independent upon the amount of substance present in the of substance present in the system . Eg:- temperature.system . Eg:- temperature.

Extensive properties are those Extensive properties are those properties whose value does properties whose value does depends upon the amount of depends upon the amount of substance present in the substance present in the system.system.

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Intensive properties

State of the systemState of the system The condition of existence of a system when The condition of existence of a system when

the macroscopic properties have definite value the macroscopic properties have definite value is called the state of the system.is called the state of the system.

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State FunctionsState FunctionsA state function A state function depends only on the present state of the systemdepends only on the present state of the system , , not on the pathnot on the path by which the system arrived at that state.by which the system arrived at that state.

•Other state functions are P, V and T.

•However, q and w are not state functions.

State variables or state State variables or state functionsfunctions

A thermodynamic property A thermodynamic property whose value depends on the whose value depends on the initial and final states of the initial and final states of the system and is independent of system and is independent of the manner by which the the manner by which the change is bought about.change is bought about.

The process which brings The process which brings changes in the system is called changes in the system is called a thermodynamic process.a thermodynamic process.

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Internal energyInternal energy The chemical nature of the The chemical nature of the

substance depends about the energy substance depends about the energy which it possesses and also which it possesses and also depends upon the state of its depends upon the state of its existence which is known as the existence which is known as the internal energy.internal energy.

It also depends upon the kinetic It also depends upon the kinetic energy of the particles in the energy of the particles in the system.system.

It is an extensive property.It is an extensive property.

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EnthalpyEnthalpy The sum of the internal The sum of the internal

energy and the sum of the energy and the sum of the pressure volume work is pressure volume work is known as the enthalpy of the known as the enthalpy of the system.system.

Enthalpy is also an extensive Enthalpy is also an extensive property.property.

Enthalpy is denoted by “H”.Enthalpy is denoted by “H”.

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Reversible and irreversible Reversible and irreversible processprocess

A reversible process is a process when it A reversible process is a process when it is carried out slowly so that the system is carried out slowly so that the system and the surroundings are always at and the surroundings are always at equilibrium then the process is termed as equilibrium then the process is termed as a reversible process.a reversible process.

An irreversible process is a process which An irreversible process is a process which takes place rapidly in the system such that takes place rapidly in the system such that the system and the surroundings are not at the system and the surroundings are not at equilibrium.equilibrium.

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The Zeroth Law of ThermodynamicsIf object A is in thermal

equilibrium with object C, and object B is separately

in thermal equilibrium with object C, then objects A and B will be in thermal

equilibrium if they are placed in thermal contact.

The First Law of ThermodynamicsThe first law of thermodynamics is a statement of the conservation of

energy.If a system’s volume is constant, and heat is added, its internal energy

increases.

The First Law of ThermodynamicsIf a system does work on the external world, and

no heat is added, its internal energy decreases.

The First Law of ThermodynamicsCombining these gives the first law of thermodynamics. The change in a system’s internal energy is related to the heat Q and the work W as follows:

The First Law of ThermodynamicsThe internal energy of the system depends only on its temperature. The work done and the heat added, however, depend on the details of the process involved.

Thermal ProcessesThis is an idealized reversible process. The gas is compressed; the temperature is constant, so heat leaves the gas. As the gas expands, it draws heat from the reservoir, returning the gas and the reservoir to their initial states. The piston is assumed frictionless.

Thermal ProcessesWork done by an expanding gas, constant pressure:

Thermal ProcessesIf the volume stays constant, nothing moves and no work is done.

Thermal ProcessesIf the temperature is constant, the pressure varies inversely with the

volume.

Thermal ProcessesThe work done is the area under the curve:

--

Thermal ProcessesAn adiabatic process is one in which no heat flows into or out of the system. The adiabatic P-V curve is similar to the isothermal one, but is steeper. One way to ensure that a process is adiabatic is to insulate the system.

Another way to ensure that a process is

effectively adiabatic is to have the volume change occur very

quickly. In this case, heat has no time to flow in or out of the

system.

Thermal Processes

Energy as Work (Energy as Work (ww) of Gas Expansion) of Gas Expansion

Work Gas Expansion

Work = - (Force x distance)

w = - (F x h)

w = - (P x A x h)

w = - P V(at constant P)

w = - nRT(at constant V)

There fore

Exchange of Heat (Exchange of Heat (H) H) by chemical systemsby chemical systems

•When heat is released by the system to the

surroundings, the process is exothermic.

•When heat is absorbed by the system from the

surroundings, the process is

endothermic.

-H

+H

q

q

Enthalpies of Reaction (Enthalpies of Reaction (H)H)The The changechange in enthalpy, in enthalpy, HH, , is the enthalpy of the is the enthalpy of the products minus the enthalpy products minus the enthalpy of the reactants: of the reactants:

HH = = HHproductsproducts −− HHreactantsreactants

This quantity, H, is called the enthalpy of reaction, or the heat

of reaction.

Reactants:

Products