lecture+01+(introduction).pdf

8/11/2019 Lecture+01+(Introduction).pdf

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Thermodynamics

Thermodynamics is the study of static (stationary) states of matter and

how they differ from one another in terms of energetic quantities

Thermodynamics is the science of energy conversion involving heat and

other forms of energy (most notably mechanical work)

Thermodynamics studies and interrelates the macroscopic variables, such

as temperature, volume and pressure, which describe physical

thermodynamic systems

Thermodynamics is a branch of physics (physical chemistry) which deals

with the energy and work of a system

Thermodynamics deals only with the large scale response of system

which we can observe and measure in experiments

Small scale gas interactions are described by the kinetic theory of gases


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Scientists related to Thermodynamics
http://upload.wikimedia.org/wikipedia/commons/8/85/Eight_founding_schools.png


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The Concept of State

Most important concept in thermodynamics is STATE

Microscopic State

A complete description of each particle in the system

The state of a system as specified by the actual properties of each individual, elemental

component, in the ultimate detail permitted by the uncertainty principle

Microscopic state of the system can be described if it is possible to know the masses,

velocities, positions, and all modes of motion of all off the constituent particles in a system

Macroscopic State

In the absence of such microscopic details, we can describe the system using macroscopic

state

When all of the properties are fixed, then the macroscopic state of the system is fixed


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The Concept of State

Macroscopic System

A system is microscopic if it is roughly of atomic dimensions or smaller

A system is macroscopic when it is large enough to be visible in the ordinary sense

The exact definition depends on the number of particles (N) in the system

A system is macroscopic if 11

N

A system is microscopic if 11

N


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Matter is described by properties

Microscopic

Speed

Force

Size

Shape

Energy

Macroscopic

Temperature

Pressure

Viscosity

Heat capacity


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Extensive and Intensive Properties

The values of extensive properties, expressed per unit volume or unit mass of the

system, have the characteristics of intensive variables

Volume Extensive property

Temperature & Pressure Intensive property

Specific volume (volume per unit mass) Intensive property

Molar volume (volume per mole) Intensive property


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States of Gases


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Pressure


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Pressure Exerted by Gases

When the pressure inside the system is equal to the pressure

outside, the system is in mechanical equilibrium with its

surroundings


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Heat is NOT a form of temperature, but can be defined in terms of

temperature.

Heat is the form of energy which passes between two bodies due

to a difference in their temperatures.

Heat always goes from the warmer body to the cooler body.

Temperature


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Thermal Equilibrium

When the temperature inside the system is equal to thetemperature outside, the system is in thermal equilibrium with

its surroundings


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Energy


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Boyles Law


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Derivation of Boyles Law

RMS velocity increases with the increase of temperature

Kinetic energy varies as the square of the velocityAccording to the kinetic theory, temperature of a gas is proportional to the mean

kinetic energy per molecule

2

2

1McKE At constant temperature, mean KE/molecule of any gas remains

constant

KEnMcnMcpV3

2

2

1

3

2

3

1 22

For a gas with definite mass, the number of molecules (n) must be a constant

Then, pV is constant at constant temperature

Total KE = Number of molecules X KE/molecule


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Illustration of Boyles Law


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Illustration of Boyles Law


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Charless Law


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Illustration of Charless Law


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Avogadros Principle (Law)

For any two gases, the kinetic gas equation can be written as

21111

21

32 cMnVp

2

22222

1

3

2cMnVp

When p1 = p2 and V1 = V2

If the two gases are also at the same T,

the mean KE is also the same

)1.(..........2

1

2

1 222

2

11 cMncMn

)2.(..........2

1

2

1 22

2

1 cMcM

Eqn (1) / Eqn (2), we get n1 = n2Equal volumes of all gases under the same

conditions of temperature and pressure

contain equal number of molecules


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Derivation of Ideal Gas Equation

Volume of a gas depends on the pressure, temperature and number of moles

(Boyles Law, Charless Law and Avogadros Principle)

pV /1 (at constant T and n) (Boyles Law)

(Charless Law)

(Avogadros Principle)

(at constant p and n)

(at constant T and p)

TV

nV

By combining these three laws,p

nTV

Ideal Gas Equation

Ideal Gas Constant

nRTpV


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Ideal Gas Constant


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Grahams Law of Diffusion

Daltons Law of Partial Pressures

___________________________________________________

Diffusion is the process by which the molecules of different substancesmingle with each other

Effusion is the process by which a gas escapes through a small hole

The rates of both depend on how fast gas molecules move (velocity)

Mixture of Gases


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Grahams Law of Diffusion

Kinetic Gas Equation is2

3

1nMcpV

nM

pVc

32

nM

pVc

3

pc

3 (Density = Total Mass / Volume)

The rate of diffusion of a gas depend on the mean velocity of its molecules

pcRatediff

3 At constant pressure (p)

1diffRate

Grahams law of diffusion states that rate of diffusion of a gas is

inversely proportional to the square root of the density of the

gas at constant pressure


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PA is the pressure gas Awould have if A were

alone in the tank

Illustration of Daltons Law

For the mixture of gases A

and B,

Pmix = PA + PB

PB is the pressure gas B

would have if B were

alone in the tank

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