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Physical Chemistry Green Technologies & Monitoring,

Semester III Lecture 1

Head of the course:

Wojciech Chrzanowski, DSc, PhD

2

Order of lectures is, perhaps, not the most logical one, but it is partially

dictated by my desire to synchronize the lectures and tutorials.

A quote of the day (good for all the semester):

The camel’s hump is an ugly lump

Which you well may see in the Zoo.

But uglier yet is the lump you get

From having too little to do.

Rudyard Kipling

Phys. Chem. GTM 01

3

Definition of a scientific discipline

Its subject: Physical and chemical transformations of the matter (without

defining its type) and associated (related) flows of energy.

Its method: Mathematical-physical, i.a., creation of theoretical models either

based on or verified by experiment. Formulation of hypotheses,

theories and laws of nature related to its subject. Cartesian-

Newtonian paradigm.

What is physical

chemistry?

Phys. Chem. GTM 01

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4

Matter is everything possessing mass (inertion, Newton).

chemical substance is a pure, isolated form of matter (amount of matter and its unit: mole, chemical species)

Energy is ability to perform work (simpl.).

(types of energy, unit: joule, J)

Fundamental concepts (1)

Equivalence of matter and energy

E=mc2

in practice, relativistic effects may be observed in the micro world only, in macroscopic world they can be neglected.

Phys. Chem. GTM 01

5

Kinetic energy – energy of motion:

Ec=½mv2 Ec=½Jω2

Fundamental concepts (2)

Potential energy – depends on the position of a body:

in the gravitational field in the electric field

of the Earth

Ep=mgh Ep=q1q2/(4pe0r)

Phys. Chem. GTM 01

Chem. Fiz. TCH II/01 6

Theoretical model is a certain assumed or imagined

mechanism of the phenomenon in question, or image plus complex of

properties of an object, usually simplified yet attempting to embrace

all its major (essential) features

Hypothesis is certain assumption on the essence of the

phenomenon under consideration, may be an attempt of guessing the

gist based upon already known concepts and laws.

Theory is a hypothesis verified in further studies

(experimentally), when it becomes confirmed (esp. in different labs)

and is applicable to many cases (objects, phenomena), frequently

related.

Fundamental concepts (3)

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Chem. Fiz. TCH II/01 7

Law of nature (physico-chemical law) is a clearly formulated

part of theory usually expressed mathematically, dealing with a

specific phenomenon , i.e., relations and links between some

observables involved in the phenomenon.

Verbal formula: Boyle’s law:

At constant temperature, volume of a gas changes inverse

proportionally to its pressure. At constant temperature, product of

volume nad pressure of a gas is constant.

Formula (equation):

Fundamental concepts (4)

const. VPPVPV ;P

P

V

V then const.if 2211

1

2

2

1 T

8

Thermodynamics (incl. thermochemistry)

Phase equilibria

Chemical equilibria

Solutions – thermodynamic charakteristics

Elektrochemistry: ionics & electrodics.

Surface phenomena

Chemical kinetics.

Main branches:

Phys. Chem. GTM 01

9

System (definition)

System is a part of universe subject to

observation or being an object of theoretical

considerations, separated from the rest of

universe (surroundings) physically or just in our

imagination.

system + surroundings = universe

Introduction to

thermodynamics

Phys. Chem. GTM 01

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10

The three types of systems:

Open

Closed

Isolated

Introduction to

thermodynamics (2)

Phys. Chem. GTM 01

11

Ways of the energy transfer:

work

heat.

Types of work

Mechanical (change of volume, change of shape), change of the interface area, electrical.

Introduction to

thermodynamics (3)

Phys. Chem. GTM 01

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HEAT

Introduction to

thermodynamics (4)

Phys. Chem. GTM 01

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13

Endothermic process (system limited by a diathermic barrier)

Introduction to

thermodynamics (5)

before after

Phys. Chem. GTM 01

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Endothermic process in an adiabatic system

Introduction to

thermodynamics (6)

before after

Phys. Chem. GTM 01

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Physical properties of systems: Extensive (additive), depending on the size of the

system (number of components, their type and amount of each)

(e.g. mass or volume of a system)

Intensive are not additive.

(e.g. temperature, density, specific and molar quantities, refraction index)

Introduction to

thermodynamics (7)

iiXnx

Phys. Chem. GTM 01

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State of a system: The following quantities permit complete characterization of the state of a given system

P, V, T

Equation of state:

f(P,V,T)=0

For a system containing perfect gas only: pV=nRT

Introduction to

thermodynamics (8)

Phys. Chem. GTM 01

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Temperatura and „zeroeth” law of thermodynamics

Two bodies, that reached the state of thermal equilibrium, have the same temperature and heat

is no more exchanged between them.

If body A is in thermal equilibrium with body B and with body C, therefore bodies B and C also remain

in thermal equilibrium.

Phys. Chem. GTM 01

Introduction to

thermodynamics (9)

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Work of expansion

Introduction to

thermodynamics (10)

dx

Pgas

Pext

dVPSdxPdw extext

FSP

2rS p

Phys. Chem. GTM 01

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Work of expansion (ctd.)

Introduction to

thermodynamics (11)

Three ways of performing the work by the system:

1. Against a constant external pressure (Pext= const).

2. Against a null external pressure (expansion to vacuum, a special

case of the latter), Pext= 0.

VPVVPdVPdww extifext

f

i

ext

f

i

0w

Phys. Chem. GTM 01

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Work of expansion (ctd.)

Introduction to

thermodynamics (12)

Phys. Chem. GTM 01

3. Reversible (quasi-static) isothermal transition: dPPPext

dVV

nRTPdVdVPdw ext

f

i i

f

f

iV

VnRT

V

dVnRTdww ln

i

f

f

i

i

f

P

PnRT

V

VnRT

V

VnRTw lnlnln

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Work of expansion (ctd.)

Introduction to

thermodynamics (13)

Phys. Chem. GTM 01

As the general expression for work of expansion is: PdVdw

f

i

f

i

dVVPdww )(and after integration:

hence, work is represented by the surface area

under the P=f(V) plot on the P-V plane .

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Thermochemistry (1)

• Enthalpy is heat exchanged at constant

pressure.

state property

• H < 0 - exothermic process

• H > 0 - endothermic process

initfinHHH

initfinHHH

Phys. Chem. GTM 01

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Thermochemistry (2)

A standard reaction enthalpy is the reaction

enthalpy when reactants in their standard

states are converted to products in their

standard states. Denoted as:

The standard state of a substance is its pure

form at pressure of 105 Pa.

0H

Phys. Chem. GTM 01

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Thermochemistry (3)

• The standard molar enthalpy of formation

of a compound is the standard reaction

enthalpy per mole of compound for the

synthesis of the compound from its

elements in their most stable forms at 105 Pa

and specified temperature. Denoted as:

00 H ;H formf

Phys. Chem. GTM 01

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Thermochemistry (4)

• Standard enthalpies of formation of

elements are equal to ZERO (at 298K).

When several allotropic forms of an

element exist, the statement applies to the

most stable form of the element.

• Standard molar enthalpy of formation of a

compound is standard molar enthalpy of

this compound.

Phys. Chem. GTM 01

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Thermochemistry (5)

ProductsReactants

initfinrreactionHHHH

fin

0

Pri,f,i H =Hn init

0

Rei,f,i H =Hn

0

Rei,f,i

0

Pri,f,i

0

r Hn-Hn=H

Phys. Chem. GTM 01

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Thermochemistry (6)

• The standard molar enthalpy of combustion is

the change in enthalpy per mole of the substance

(fuel) when it is burned (reacts with oxygen)

completely under standard conditions. Denoted as

• conditions superimposed on products in complete

combustion:

H H2O(l); C CO2(g); N N2(g)

00 H ;H combc

Phys. Chem. GTM 01

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Thermochemistry (7)

Using standard molar enthalpies of combustion

one can calculate the reaction enthalpy as follows:

This is an exceptional formula, where a property

of the products is subtracted from that of the

reactants.

0

Pri,c,i

0

Rei,c,i

0

r Hn-Hn=H

Phys. Chem. GTM 01

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Hess law

A reaction enthalpy is the sum of the enthalpies of

any sequence of reactions (all at the same

temperature and pressure) into which the overall

reaction may be divided.

Hess's law results from a rigorous application of the statement

that enthalpy is a state property. It does not matter what was the

way to obtain the substance or into how many steps the overall

reaction was split.

Phys. Chem. GTM 01

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Hess law (2)

Hess law may be applied to each and every state

quantity (not only to enthalpy).

Another wording:

If any reaction (target reaction) may be represented

as a linear combination of some other reactions

(partial reactions) then any state property of this

reaction is the same linear combination of the

respective state properties of the partial reactions.

Phys. Chem. GTM 01

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Hess law (3)

Thermochemical equations:

1. State of matter (phase: solid, liquid, gaseous) and

any specific form of all reactants and products must

be indicated.

2. The heat released or absorbed, i.e., the H must be

shown.

Phys. Chem. GTM 01

CBAT HHH2H

then2 If

CBAT

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Hess law (4)

Rules of manipulation:

1. When the reaction is rewritten in reversed direction,

the sign of its H is changed.

2. When stoichiometric coefficients in the reaction are

multiplied, the H must be multiplied by the same

factor.

3. When two reactions are added, their enthalpy

changes must be added, too.

Phys. Chem. GTM 01

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Hess law. Example

Target reaction:

Component reactions:

Step 1. Begin with the thermochemical equation having at

least one of the reactants or products on the correct side of

the arrow in the target reaction:

?H O(l);H+(g)2CO(g)O2+(g)HC :T 0

T22221

22

mol]226.75[kJ/=H (g);HC(g)H+2C(s) :A 0

A222

mol]-393.5[kJ/=H (g);CO(g)O+C(s) :B 0

B22

mol]-285.9[kJ/=H O(l);H(g)O+(g)H :C 0

C2221

2

Phys. Chem. GTM 01

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Hess law. Example (2)

Hence, we start with reaction B and multiply both sides (as

well as its standard enthalpy) by a factor of 2:

Step 2. To add a reactant or product, add another reaction,

having the desired substance at the same side of the arrow

as in the overall reaction. To cancel a reactant or product

(which is not present in the target reaction), add another

reaction, having the desired substance at the opposite side of

the arrow than in the reaction obtained so far.

2B=D (g);2CO(g)2O+2C(s) 22

Phys. Chem. GTM 01

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Hess law. Example (3)

In our case, to complete the right side of reaction (T), we

add reaction (C) to reaction (D):

Step 3. If the reaction obtained in step 2 is identical with

reaction T, then the procedure is completed, else - repeat

step 2 (do not use reactions already used in it).

In our case, reaction (E) is not yet equal to reaction (T).

We repeat step 2 to eliminate carbon and hydrogen at the

left side of reaction (E), by adding reversed reaction (A) to

reaction (E) or subtracting (A) from (E).

C+2B=E O(l);H+2CO(g)O2+(g)H+2C(s) 22221

2

Phys. Chem. GTM 01

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Hess law. Example (4)

Our goal is achieved. Reaction (F) is equal to reaction (T).

The linear combination we found is T=2B+C–A. We

calculate the change in enthalpy in reaction (T) in the same

manner:

T=A-C+2B=F O(l);H+2CO(g)O2+(g)HC 22221

22

J/mol]-1299.65[k= ...

...=(-226.75)+(-285.5)+-393.52=H-H+H2=H 0

A

0

C

0

B

0

T

Phys. Chem. GTM 01

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Hess law – algorithm

Phys. Chem. GTM 01

S

E

Select a reaction, possibly containing specific compounds from reaction T

Select another reaction and add it to (subtract from) the one already obtained.

Is the reaction obtained the same as

reaction T?

Yes

No