INTRODUCTION :
It is a well known fact that most of the phyiscal changes and chemical changes are accompained by energy changes. these energy changes may take place in the form of heat, light, work, electical changes, etc. All these forms of energy are convertible into one another and hence are related to each other quantitatively.
“The branch of science which deals with th estudy of different forms of energy and the quantitative relation ship between them is known as thermodynamics.
The name thermodynamics is given by the mechanicals engineers in the beginning whon were intrested in only in the conversion of heat into mechanical work. Thermo means heat and dynamics means motion resulting into mechanical work.
NEED FOR THE LAW AND DIFFERENT STATEMENTS OF THE LAW .
According to the first law of thermodynamics ‘ one form of energy can be converted into another form and the total amount of the energy can be conserved ‘ the 1st law gave us the two important state functions E and H , still have some limitations
Due to this limitations , it becomes very necessory to introduce an another law of thermodynamics to overcome those limitations .
LIMITATIONS OF 1ST LAW OF THERMODYNAMICS:
As discussed earlier the 1st law of thermodynamics tell us about the conservation of the energy during any chemical or physical process. but this law doesn’t tell about the feasiblity of a process, i.e, whether the process under the given conditions is feasible or not.
For example , if we burned a papper of a piece in the presence of oxygen , the reverse can not be happen, from ashes paper can not form.
similarly, a bottle of a perfume is opend in a room, it’s vapour spreads in the whole room but the reverse process, i.e, vapours of perfume can not collect themselves in the bottle.
similarly , a gas can expand into vaccum and the process doesn’t violate first law of thermodynamics but the reverse can not be happened.
you have a question in a mind that why all the process above explained are uni-directional in nature ,i.e, occurs only in one direction from products —–> reactants. and cannot be reversed under the similar set of conditions. answers of such questions could not answered by 1st law of thermodynamics.
The answers of these questions was given by 2nd law of thermodynamics . the law states that ‘all the natural and spontaneous phenomenons/processes are unidirectional and irreversible in nature .
For example , the processes like flow of water from up hill to down hill , flow of haet from hot end to cold end, and diffusion of gas from high pressure to a l ow pressure. etc….. all these processes are unidirectional and thermodynamiocally irreversible in nature.
Here , in the above statement of 2nd law of thermodynamics , a term ‘SPONTANEOUS PROCESS.’ is used.
The term spontaneuos means — themselves, and spontaneous process means that the processes may occur themselves , with out any help of external stimulai.
IMPORTANT POINTS ABOUT SPONTANEOUS ;
(a) The spontaneous processes do not proceed in the reverse direction themselves. For example, water will not go uphill by itself. however the spontaneous processes can be reversed with the help of any external factors
(b) The term ‘spontaneous’ doesn’t give any idea about the rate at which the process occurs.
SECOND LAW OF THERMODYNAMICS.
Now lets consider the conversion of heat into work . According to the 1st law of thermodymaics there is an eqivalence between heat absorbed and the work obtained but the heat absorbed can not be completely converted into work without leaving some changes in the system or surroundings. for example heat produced in a steam engine can not completely converted into mechanical work because a part of heat wasted in overcoming the friction. according to this second law of thermodynamics may be stated as :
it is impossible to convert heat into equivalent amount of work with out leaving some changes on the system or surroumdings .
The second law of thermodynamics can also be stated in a number of other forms which we will discuss at various stages in this article . but there are two more common and important forms of second law of thermodynamics are:
1. heat can not flow from a cold body to a hot body with out use of an extrernal agency and,
2. it is impossible to construct a machine , functioning in cycles, which can convert heat completely into an equuivalent amount of work without producing some changes elsewhere in the system.
thank you dear learners that’s all for today see you in next article
In the next article we will discuss about cyclic processes.
InoOP Chem 