Thermodynamics
· This term consists of Thermo means
Heat/energy) and Dynamics means motion.
· Thermodynamics is the branch of
science which deals with the various forms of energy and their transformation during
all physical and chemical processes.
but
Chemical thermodynamics is the branch of thermodynamics which deals with the
study of energy changes taking place in chemical processes.
Advantages of thermodynamics:
· It gives information about various
thermodynamic laws.
· It helps us to predict whether a given
chemical reaction will take place or not under the given set of conditions.
· It gives information about various
energy changes.
Limitations of thermodynamics:
· The lows of thermodynamics apply to the
properties like temperature, pressure, volume, etc of matter in bulk but
doesn't tell us anything about the individual properties of atoms or molecules.
i.e., Thermodynamics deals with macroscopic system but not with
microscopic system.
· It tells us whether a given chemical
reaction will take place or not under the given set of conditions but doesn't
tell us anything about how and at what rate of the energy transformations are
carried out. i.e., it does not tell about the rate of reaction.
Thermodynamic terms:
System: is defined as a
specified part of the universe or specified portion of the matter which
is under experimental investigation
Surrounding: is defined as the
remaining part of the universe which is not the part of the system.
Universe = System +
Surrounding
Boundary: Anything which separates system and surrounding is called boundary. Boundary can be categorised into three types.
a.
conducting or non-conducting nature of boundary.
b.
Boundary can be rigid or non-rigid.
c.
Boundary can be real or imaginary.
For example: A reaction is carried out in a test
tube. The contents of test-tube constitute the system, test tube serves as
boundary and anything which is outside the test-tube is called surroundings.
Type of systems:
There are three types of systems
a). Open system: a system which can exchange energy as well as matter with the surrounding is called open system. The boundary is neither sealed nor insulated. Total mass will not remain constant. Example-Tea in open glass
b). Closed system:
· a
system which can exchange energy but not matter with its surroundings is called
closed system.
· The
boundary is sealed but not insulated.
· Amount
of the system will remain constant.
· Example-
Hot water in closed vessel, Glowing bulb, tube light.
c). Isolated system:
·
a system which can neither exchange mass nor
energy with the surroundings is called an isolated system.
· boundary
is sealed and insulated. Universe can be considered as an isolated system. Example-Coffee
in thermos-flask.
State of system-
The
state of the system is defined by their measurable properties like temperature,
pressure, volume etc.
If any of these properties change, state of
the system is said to be changed.
State variables-
Properties which define state of any
system are called its state variables or thermodynamic variables or
thermodynamic quantities
State Function:
·
Those state variables which depend only upon
initial and final state of the system but doesn't depend upon the path or
mechanism followed by the system to achieve final state are called state
function.
· State functions are denoted by capital letters. Ex. E, H, S, G, T, P, V etc
Path function:
· Properties
of the system which depend upon the initial and final state of the system as
well as the path or mechanism followed by the system to achieve final state are
called path function.
· Path
functions are denoted by small letters. Example- Work (w), Heat(q).
Type of process-
The state of a
thermodynamic system can be changed by a process. These may be
a). Isothermal process- defined as a process which
takes place at constant temperature.
b). Isobaric process- defined as a process which
takes place at constant pressure.
c). Isochoric process- defined as a process which
takes place at constant volume.
d). Adiabatic process- a process in which the system
does not exchange heat with the surroundings is called adiabatic process. But The
temperature pressure, volume of the system varies.
e). Irreversible process- A process which is not
reversible is called an irreversible is called an irreversible is called an
irreversible process.
In this process driving force is very different than the
opposing force. Ex- all-natural process.
f). reversible process- proceeds infinitely slowly. In
this process driving force is infinitesimally small difference than the
opposing force.
g).Cyclic Process : When a system undergoes a number of different processes and finally returns to its initial state, it is termed as cyclic process. In cyclic process change in all state function will be zero. i.e., ΔE = 0, ΔH = 0, ΔP = 0, ΔT = 0
Thermodynamic properties:
the properties which arise from the bulk behaviour of matter
are called macroscopic properties.it can be sub-divided into two types-
These are as
a). Intensive properties
b). Extensive
properties
|
S.no. |
Intensive
properties |
Extensive
properties |
|
1 |
The
properties of the system which do not depend upon the amount or size of
matter present in system are called intensive properties. |
The
properties of the system which depend upon the amount or size of matter
present in system are called extensive properties. |
|
2 |
Example- Temperature, pressure,
viscosity, surface tension, dielectric constant, molar properties (as mole
fraction, molar volume, molar heat capacity), vapour pressure, Boiling point,
freezing point, PH value, Cell potential etc. |
Example- mass, volume,
surface area, internal energy, enthalpy, entropy, free energy, heat capacity
etc. |
Internal energy:
Internal energy: We know that every substance passes some energy since its origin.
so the internal energy is the sum total of all the energies possessed by the system .
☝It is denoted by U.
☝It is a state function.
☝It is an extensive property.
☝U of the system may be changed when
a) q passes or out of the system
b) work is done on or by the system
c) matter enters or leaves the system
Change in Internal Energy by Doing Work-
