Забыли?

?

# Презентация

код для вставкиСкачать
LECTURE 6
THEME: Theoretic
bases of bioenergetics.
ass. prof. Yeugenia B. Dmukhalska
PLAN
пѓ� Introduction of thermodynamics. Main
concepts.
пѓ� Internal energy; work; heat.
пѓ� First law of the thermodynamics.
пѓ� Enthalpy. The HessвЂ™s law. Standard
enthalpy changes.
пѓ� Second law of the thermodynamics.
Entropy. GibbsвЂ™ energy.
Definition
вЂў 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
вЂў The part of the universe chosen for
thermodynamic consideration (to study the effect
of temperature, pressure etc.) is called Р° system.
вЂў The remaining portion of the universe, excluding
the system, is called surroundings.
вЂў Рђ system usually consists of Р° definite amount of
one or more substances and is separated from the
surroundings by Р° real or imaginary boundary
through which matter and energy can flow from
the system to the surroundings or vice versa.
Types of systems
вЂў A system is said to be an OPEN SYSTEM if it
can exchange both matter and energy with the
surroundings.
вЂў If Р° system can exchange only energy with the
surroundings but not matter, it is called Р°
CLOSED SYSTEM.
вЂў If Р° system can neither exchange matter nor
energy with the surroundings, it is called an
ISOLATED SYSTEM.
State of Р° system and state
variables.
вЂў The state of Р° system means the condition of the
system, which is described in terms of certain
observable (measurable) properties such as
temperature (Рў), pressure (P), volume (V) etc. of
the system.
вЂў If any of these properties of the system changes,
the system is said to be in different state i.Рµ. the
state of the system changes. That is why these
properties of Р° system are called state variables.
Properties of systems.
вЂў 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.
вЂў 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.
вЂў 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 Р° system.
Thermodynamic processes.
вЂў Isothermal process. When Р° process is carried out in such Р° manner
that the temperature remains constant throughout the process, it is
called an isothermal process.
вЂў Adiabatic process. When a process is carried out in such Р° 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
вЂў Isochoric process. It is Р° process during which the volume of the
system is kept constant.
вЂў Isobaric process. It is Р° process during which the pressure of the
system is kept constant.
вЂў Рђ reversible process is Р° 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.
вЂў On the other hand, Р° process which does not meet the above
requirements is called an irreversible process.
вЂў
вЂў
вЂў
вЂў
INTERNAL ENERGY
It is the sum of different types of energies associated
with atoms and molecules such as electronic energy
(Р•e), nuclear energy (Р•n), chemical bond energy (Р•c),
potential energy (Р•СЂ) and kinetic energy (Р•k) which is
further the sum of translational energy (Р•t), vibrational
energy (Р•v) and rotational energy (Р•r).
Р• = Р•e + Р•n + Р•СЃ + Р•СЂ + Р•k
or U = Ue + Un + UСЃ + UСЂ + Uk
The energy thus stored within Р° substance (or Р° system)
is called its internal energy and is usually denoted by
the symbol вЂњР•вЂќ or вЂњUвЂќ.
вЂў The first law of thermodynamics is simply
the law of conservation of energy which states
that.
вЂў Energy can neither be created nor
destroyed although it may be converted
from one form to another
вЂў 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.
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
Р•2 = E1 + q + W or (U2 = U1 + q + A)
or Р•2 вЂ“ E1 = q + W or (U2 вЂ“ U1 = q + A)
or пЃ„Р• = q + W (or пЃ„U = q + A)
If W = p пЃ„V (or A = p пЃ„V ) so
пЃ„Р• = q вЂ“ P пЃ„V (or пЃ„U = q вЂ“ P пЃ„V )
or q = пЃ„Р• + P пЃ„V (or q = пЃ„U + P пЃ„V)
E (U)вЂ“ internal energy;
q вЂ“ heat;
W (A) вЂ“ work;
V вЂ“ volume.
Enthalpy
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
If Р° process is carried out at constant pressure:
W = вЂ“ PпЃ„V;
q = пЃ„E вЂ“ W; qp = пЃ„E вЂ“ PпЃ„V;
пЃ„E = E2 вЂ“ E1; пЃ„V = V2 вЂ“ V1;
qp = (Р•2 вЂ“ E1) + Р (V2 вЂ“ V1) or
qp = (Р•2 + Р V2) вЂ“ (E1 + Р V1)
Рќ=Р• + PV; Рќ2 = Р•2 + PV2; H1 = E1 + PV1
qp = Рќ2 вЂ“ H1 or qp = пЃ„Рќ
пЃ„Рќ = Рќ2 вЂ“ H1 is the enthalpy change of the system.
пЃ„Рќ = пЃ„E + PпЃ„V
Hess's law
вЂў 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
вЂў 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.
вЂў Standard enthalpy change (пЃ„Рќ0) вЂ“ the enthalpy change are
reported under standard conditions which are 1 atm pressure
and 298 Рљ.
вЂў The standard enthalpy of formation (пЃ„Рќ0f) 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.
вЂў The enthalpy of formation of any element in the standard
state is taken as 'zero'. пЃ„Рќ0(formation) = 0
вЂў 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.
вЂў Calculation of enthalpies of reactions.
вЂў пЃ„Рќ=(Sum of the standard enthalpies of
formation of products) вЂ“ (Sum of the
standard enthalpies of formation of
reactants)
вЂў пЃ„Рќreaction
=
пЃ“пЃ„Рќ0(Products)
вЂ“
пЃ“пЃ„Рќ0(Reactants);
вЂў Bond energy usually means bond dissociation
energy.
вЂў пЃ„Рќreaction = пЃ“ пЃ„Рќ0(Products) вЂ“ пЃ“ пЃ„Рќ0(Reactants)
вЂў пЃ„Рќreaction = пЃ“ пЃ„Рќ0(Bond Energies of Reactants
reaction) - пЃ“ пЃ„Рќ0(Bond Energies of Products)
Spontaneous and non-spontaneous
processes
вЂў
вЂў
вЂў
вЂў
вЂў
вЂў
Spontaneous processes:
(i) Tendency for minimum energy
(ii) Tendency for maximum randomness.
non-spontaneous processes:
Tendency for maximum energy
Tendency for minimum randomness.
вЂў Entropy is a measure of randomness or disorder of the
system
вЂў пЃ„G = пЃ„H вЂ“ TпЃ„S - second law
вЂў THIRD LAW OF THERMODYNAMICS:
вЂў The entropy of all perfectly crystalline solids may be
taken as zero at the absolute zero of temperature.
###### Документ
Категория
Презентации
Просмотров
30
Размер файла
1 620 Кб
Теги
1/--страниц
Пожаловаться на содержимое документа