Thermodynamics and Thermodynamic terms:

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-

Let us bring the change in the internal energy by doing work.

Let the initial state of the system is state A and Temperature TA 

Internal energy = UA

On doing’some mechanical work the new state is called state B and the temp. TB, internal energy of it UB It is found to be

           TB > TA

UB is the internal energy after change.ΔU = UB – UA

Change in Internal Energy by Transfer of Heat

Internal energy of a system can be changed by the transfer of heat from the surroundings to the system without doing work                                      

                                 ΔU = q

Where q is the heat absorbed by the system. It can be measured in terms of temperature difference.

q is +ve when heat is transferred from the surroundings to the system. 

q is -ve when heat is transferred from system to surroundings.

First law of thermodynamics-

When change of state is done both by doing work and transfer of heat.Then internal energy will be                                          ΔU = q + w

First law of thermodynamics

(Law of Conservation of Energy). It states that, energy can neither be created nor be destroyed. The energy of an isolated system is constant.

                                 ΔU = q + w.