Download 06. Theoretic bases of bioenergetics

LECTURE 6
THEME: Theoretic
bases of bioenergetics.
ass. prof. Yeugenia B. Dmukhalska
PLAN
 Introduction of thermodynamics. Main
concepts.
 Internal energy; work; heat.
 First law of the thermodynamics.
 Enthalpy. The Hess’s law. Standard
enthalpy changes.
 Second law of the thermodynamics.
Entropy. Gibbs’ energy.
Definition
• The branch of science, which deals with the
study of different forms of energy and the
quantitative relationships between them is
known as thermodynamics.
System and Surroundings
• The part of the universe chosen for
thermodynamic consideration (to study the effect
of temperature, pressure etc.) is called а system.
• The remaining portion of the universe, excluding
the system, is called surroundings.
• А system usually consists of а definite amount of
one or more substances and is separated from the
surroundings by а real or imaginary boundary
through which matter and energy can flow from
the system to the surroundings or vice versa.
Types of systems
• A system is said to be an OPEN SYSTEM if it
can exchange both matter and energy with the
surroundings.
• If а system can exchange only energy with the
surroundings but not matter, it is called а
CLOSED SYSTEM.
• If а system can neither exchange matter nor
energy with the surroundings, it is called an
ISOLATED SYSTEM.
State of а system and state
variables.
• The state of а system means the condition of the
system, which is described in terms of certain
observable (measurable) properties such as
temperature (Т), pressure (P), volume (V) etc. of
the system.
• If any of these properties of the system changes,
the system is said to be in different state i.е. the
state of the system changes. That is why these
properties of а system are called state variables.
Properties of systems.
• Extensive properties. These are those
properties which depend upon the quantity
of the matter contained in the system. The
common examples of these properties are
mass, volume and heat capacity. And some
other properties internal energy, enthalpy,
entropy, Gibbs free energy etc.
• Intensive properties. These are those properties
which depend only upon the nature of the
substance and are independent of the amount of
the substance present in the system. The
common examples of these properties are
temperature, pressure, refractive index, viscosity,
density, surface tension, specific heat, freezing
point, boiling point, etc.
• It is because pressure and temperature are
intensive properties, independent of the quantity
of the matter present in the system that they are
frequently used as variables to describe the state
of а system.
Thermodynamic processes.
• Isothermal process. When а process is carried out in such а manner
that the temperature remains constant throughout the process, it is
called an isothermal process.
• Adiabatic process. When a process is carried out in such а manner
that no heat can flow from the system to the surroundings or vice
versa i.e the system is completely insulated from the surroundings, it
is called an adiabatic process.
• Isochoric process. It is а process during which the volume of the
system is kept constant.
• Isobaric process. It is а process during which the pressure of the
system is kept constant.
• А reversible process is а process which is carried out infinitesimally
slowly so that all changes occurring in the direct process can be
exactly reversed and the system remains almost in a state of
equilibrium with the surroundings at every stage of the process.
• On the other hand, а process which does not meet the above
requirements is called an irreversible process.
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INTERNAL ENERGY
It is the sum of different types of energies associated
with atoms and molecules such as electronic energy
(Еe), nuclear energy (Еn), chemical bond energy (Еc),
potential energy (Ер) and kinetic energy (Еk) which is
further the sum of translational energy (Еt), vibrational
energy (Еv) and rotational energy (Еr).
Е = Еe + Еn + Ес + Ер + Еk
or U = Ue + Un + Uс + Uр + Uk
The energy thus stored within а substance (or а system)
is called its internal energy and is usually denoted by
the symbol “Е” or “U”.
• The first law of thermodynamics is simply
the law of conservation of energy which states
that.
• Energy can neither be created nor
destroyed although it may be converted
from one form to another
• The total energy of the universe (i.e. the
system and the surroundings) remains
constant, although it may undergo
transformation from one form to the other.
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Е2 = E1 + q + W or (U2 = U1 + q + A)
or Е2 – E1 = q + W or (U2 – U1 = q + A)
or Е = q + W (or U = q + A)
If W = p V (or A = p V ) so
Е = q – P V (or U = q – P V )
or q = Е + P V (or q = U + P V)
E (U)– internal energy;
q – heat;
W (A) – work;
V – volume.
Enthalpy
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If а process is carried out at constant pressure:
W = – PV;
q = E – W; qp = E – PV;
E = E2 – E1; V = V2 – V1;
qp = (Е2 – E1) + Р(V2 – V1) or
qp = (Е2 + РV2) – (E1 + РV1)
Н=Е + PV; Н2 = Е2 + PV2; H1 = E1 + PV1
qp = Н2 – H1 or qp = Н
Н = Н2 – H1 is the enthalpy change of the system.
Н = E + PV
Hess's law
• The total amount of heat evolved or
absorbed in a reaction depends only upon
the nature of the initial reactants and that of
the final products and does not depend upon
the path by which this change is brought
about. In other words, the total amount of
heat evolved or absorbed in a reaction is
same whether the reaction takes place in
one step or a number of steps.
CALORIMETER
• Enthalpy of reaction is defined as the amount of heat
evolved or absorbed when the number of moles of the
reactants as represented by the balanced equation have
completely reacted. Its value depends upon the conditions of
temperature and pressure.
• Standard enthalpy change (Н0) – the enthalpy change are
reported under standard conditions which are 1 atm pressure
and 298 К.
• The standard enthalpy of formation (Н0f) is defined as
the enthalpy change that takes place when one mole of the
substance under standard conditions is formed from its
constituent elements in their most stable form and in their
standard state.
• The enthalpy of formation of any element in the standard
state is taken as 'zero'. Н0(formation) = 0
• The enthalpy of combustion of a substance is defined as
the amount of heat evolved when 1 mole of the substance is
completely burnt or oxidized.
• Calculation of enthalpies of reactions.
• Н=(Sum of the standard enthalpies of
formation of products) – (Sum of the
standard enthalpies of formation of
reactants)
• Нreaction
=
Н0(Products)
–
Н0(Reactants);
• Bond energy usually means bond dissociation
energy.
• Нreaction =  Н0(Products) –  Н0(Reactants)
• Нreaction =  Н0(Bond Energies of Reactants
reaction) -  Н0(Bond Energies of Products)
Spontaneous and non-spontaneous
processes
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Spontaneous processes:
(i) Tendency for minimum energy
(ii) Tendency for maximum randomness.
non-spontaneous processes:
Tendency for maximum energy
Tendency for minimum randomness.
• Entropy is a measure of randomness or disorder of the
system
• G = H – TS - second law
• THIRD LAW OF THERMODYNAMICS:
• The entropy of all perfectly crystalline solids may be
taken as zero at the absolute zero of temperature.