Thermodynamics NSU.ppt

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Thermodynamics

Dr. Mohammad Shariare

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What is thermodynamics ?

 _{The study of the flow of heat or any other form of energy}

into or out of a system as it undergoes a physical or chemical transformation, is called Thermodynamics.

 _{Thermodynamics} _{is the physics of} _energy_, _heat_, _work_,

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Laws of thermodynamics

The study of thermodynamics is based on

three

broad

generalizations.

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Thermodynamics

Scope of Thermodynamics:

1. Most of the important laws of the physical chemistry (i.e., Phase Rule,

Distribution Law) can be derived from the laws of thermodynamics.

2. It tells whether a particular physical or chemical change can occur

under a given set of conditions of temperature, pressure and

concentration.

3. It also helps to predict how far a change can proceed untill the

equilibrium.

Limitations of Thermodynamics:

1. Thermodynamics is applicable to macroscopic systems.

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Thermodynamics



_Work:

Work

(

W

) is the energy transferred in applying force over a

distance.

Work can be calculated from the formula:

Simple formula: W = Fs

Where,

F

is the force and

s

is the distance traveled by the

object.

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Thermodynamics

The

SI derived unit

of work is the

Joule

, which is

defined as the work done by a force of one

newton

acting over a distance of one

metre

in the

direction of the force

.

Other units include the

erg

, the foot-pound , and

the foot-poundal.

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Thermodynamics

Energy:

Energy is the capacity to do work.

The SI unit for both energy and work is the joule (J).

There are different types of energy which are described as follows:

• Thermal energy is the energy associated with the random motion of atoms and molecules

• Chemical energy is the energy stored within the bonds of chemical substances

• Nuclear energy is the energy stored within the collection of neutrons and protons in the atom

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Thermodynamics

Kinetic energy:

Kinetic energy (also called living force) is energy possessed by a body by virtue of its motion.

kinetic energy of a body with mass (m), whose centre of mass is moving in a straight line with linear velocity (v), we can use the newtonian approximation:

E = mv2_/2

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Thermodynamics

o _{Potential energy}₍_U_{, or}_Ep)_{is energy by virtue of matter being}

able to move to a lower-energy state, releasing energy in some form.

o _{Chemical energy is a form of potential energy related to the}

breaking and forming of chemical bonds .

Potential energy:

o The internal energy of a system (abbreviated E or U) is the total kinetic energy due to the motion of molecules and

o The total potential energy associated with the rotational, vibrational and electric energy of atoms within molecules.

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Thermodynamics

• _Greek_en_{= in;}_thalpos_{= heat}

• _{The total heat content of a system (at constant pressure) is}

called Enthalpy.

• _{Enthalpy (H)}_{is used to quantify the heat flow into or out}

of a system in a process that occurs at constant pressure.

∆H = H (products) – H (reactants)

∆H = heat given off or absorbed during a reaction at constant pressure

• Unit of Enthalpy is kcal or kJ.

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Thermodynamics

Heat Capacity of a system is the heat absorbed by unit mass in raising the temperature by one degree (K or 0_{C). It is given by c.}

Heat capacity:

The molar heat capacity of a system is defined as the amount of heat required to raise the temperature of one mole of the substance by 1 K. The molar heat capacity may be defined as the ratio of the amount of heat absorbed to the rise in temperature.

C = dq/dT

Units: cal/K/mole, J/K/mol

Molar Heat capacity:

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Thermodynamics

 _{Heat capacities are also compared for one gram amounts of}

substances.

 _The_{specific heat capacity}_{(or “specific heat”) is the}_heat

required to raise the temperature of one gram of a substance by one degree Celsius.

Specific heat capacity:

Q = s x m x ∆T

 the specific heat = s,

 mass in grams = m, and

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Thermodynamics

 _{Calculate the heat absorbed when the temperature of 15.0}

grams of water is raised from 20.0 oC to 50.0 oC. (The specific

heat of water is 4.184 J/g.o_C.)

q = s x m x ∆T

)

C

0 .

20

0 .

50 (

)

g

0 .

15 (

)

184 .

4 (

q

_gJ_C o

o







_

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Thermodynamics

Isothermal Process:

 In this process a reaction is carried out in a system which kept under constant temperature, the reaction is said to be conducted isothermally.

Adiabatic Process:

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Thermodynamics

Joule-Thomson Effect:

The phenomena of producing lowering of temperature when a gas is made to expand adiabatically from a region of high pressure into a region of low pressure, is known as Joule-Thomson Effect or Joule-Kelvin Effect.

Spontaneous process:

A process which proceeds of its own accord, without any outside assistance, is termed a spontaneous or natural process.

In general, the tendency of a process to occur naturally is called the spontaneity.

Spontaneous

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Thermodynamics

• Entropy

is a thermodynamic state quantity. It is a measure

of the randomness or disorder of the molecules of the

system.

• _{Symbol: S}

• _{Change in entropy: Δ S}

Δ S = S

_final

- S

_initial

• _{A process accompanied by an increase in entropy tends to}

be spontaneous.

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First law of Thermodynamics

First Law is known as the Law of Conservation of Energy. This law can be expressed as:

• Energy may be transformed from one form to another, but the total

energy of any body or system of bodies is a quantity that can be neither increased nor diminished (thermodynamic)

• Whenever energy of a particular type disappears equivalent amount of another type must be produced.

The first law of thermodynamics can be expressed mathematically as follows:

int

E

Q W

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Second law of Thermodynamics

• Whenever a spontaneous process takes place, it

is accompanied by an increase in the total

energy of the universe.

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Third law of Thermodynamics

• At absolute zero, the entropy of a perfectly

crystalline substance is also zero, because the

crystal arrangement shows the greatest

orderliness at this temperatuer.

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Thermodynamics

Thermodynamic Systems:

A thermodynamic

system

is that part of the universe that is

under consideration.

A real or imaginary

boundary

separates the system from the

rest of the universe, which is referred to as the

environment

.

System + Surroundings = Universe

Thermodynamic state:

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Thermodynamics

Isolated systems: not exchanging heat, matter or work with their environment.

Closed systems: exchanging energy (heat and work) but not matter with their environment.

Open systems: exchanging energy (heat and work) and matter with their environment. A boundary allowing matter exchange is called permeable. The ocean would be an example of an open system.

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Thermodynamics

SURROUNDINGS

SYSTEM

open

closed

isolated

Exchange: mass &

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Thermodynamics

 _{Reversibility}_{is the ability to run a process back and forth infinitely} without losses.

 _{Reversible Process:}_{The process that takes place infinitesimally} slowly and the direction of change at any point can be reversed by an infinitesimal change in the state of the system.

 _{Example: Perfect pendulum}

 _{Irreversible Process:}_{When a process goes from the initial to the} final state in a single step and cannot be reversed, it is called an

irreversible process.

 _{Example: when we are driving the car uphill, it consumes a lot of}

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Thermodynamics

Reversible process Irreversible process

It take infinite time to occur It takes place in finite time

It is imaginary It is real

It is in equilibrium in all stages of operation

It is in equilibrium at initial and final stages only

Changes can be reversed Changes can not be reversed. It is extremely slow It proceeds at measurable speed

Work done by reversible process is greater than the work in

irreversible process

Work done by irreversible process is smaller than the work in reversible

process

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Thermochemistry

is the study of the quantity of

heat absorbed or evolved by chemical reactions.

• An equation which indicates the amount of heat change (evolved or absorbed) in the reaction or process is called a Thermochemical Equation.

• _{The equation must be balanced}

• Values of H must be given.

• The physical states of all reactants and products must be specified in thermochemical equations.

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Thermochemistry

• Heat of reaction

or

Enthalpy of reaction

may be defined

as the amount of heat absorbed or evolved in a reaction

when the number of moles of reactants (as represented by

the balanced chemical equation) change completely into

products.

P

₄

(

s

) + 5O

₂

(

g

) P

₄

O

₁₀

(

s

) ∆

H

= -3013 kJ

• _{Standard Heat Change or Standard Enthalpy}

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Thermochemistry



_{The standard enthalpy of formation}

_{of a substance,}

denoted

∆H

_fo

_{, is the enthalpy change for the formation of}

one mole of a substance in its standard state from its

component elements.



H

₂

O (g)

∆ H

_fo

= 57.84 Kcal/mole

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Thermochemistry

The

enthalpy of solution (



H

_soln

) is the heat generated or

absorbed when a certain amount of solute dissolves in a certain

amount of solvent.

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Thermochemistry

H

₂

O

(l)

H

₂

O

(g)



H

= 44.0 kJ

H

₂

O

(s)

H

₂

O

(l)



H

= 6.01 kJ

The Heat or enthalpy of fusion is the change in enthalpy resulting from heating one mole of a substance to change its state from a solid to a liquid. The temperature at which this occurs is the melting point.