THERMODYNAMICS LAW

It is a branch of science that deals with the energy and its changes or with conservation of energy is called thermodynamics.

UNIT OF HEAT OR ENERGY:-

The units of heat or energy are calories , joule 1 cal = 4.18 J.

THEMOCHEMISTRY:-

Brach of chemistry which deals with the changes of energy in chemical reactions is called thermo chemistry.

THERMO CHEMICAL REACTION:-

Reaction in which changes of energy or heat take place are called thermo chemical reaction.

TYPES OF THERMO CHEMICAL REACTIONS:-

1) EXOTHERMIC  REACTION:-

That reactions in which heat is released when reactant change into product are called exothermic reactions.

Reactan ------> Product + heat

C + O2-------> CO2 + 394kj

In this case reactants are highly energy than the products so when they change into product then heat ia released.

ENDOTHERMIC REACTION:-

Reactions in which heat is absorbes when reactants change into product are called endothermic reactions.

Reactant + heat-----> Product

C + H2O + 131kj ----> CO + H2

In this case reactant are at low energy than the products so when they change into product then heat is absorbed.

Three things which are effected in the chemical reactions.

SYSTEM:-

 Any part of matter or unverse which is under the observation of experiment is called system.

Surrounding:-

 Any part of matter or universe which affect the system or bring change in system is called surroundings.

Or Enviroment of system is called surrounding.

Boundary 

Any imaginary or real part of matter or universe which separate the system and surrounding is called boundary.

EXAMPLE No 1: 

If we take acrtic acid and ethyl alcohol in a test tube to form ester and test tube place in a thermostat then the chemical in a test tube are system and the thermostat is surrounding while test tube is boundary.

EXAMPLE No 2:

If we take water in a beaker and take it inti refrigerator to change it in ice then water is system and the refrigerator is surrounding while beaker is boundary.

PROPERTIES OF SYSTEM

A system has two types of properties.

1)EXTENSIVE PROPERTIES:-

Property of system which depands upon the amount of a system is called extensive properties.Change in the value of extensive properties depands on the change in amount of system.If amount of system is double then it's extensive properties will also double and if it is divided into two parts (halves) then extensive properties will be divided in to two parts(halves) .

EXAMPLE:- Mass , Volume , Lenght , Heat , Gibb's free energy etc
.

2)INTENSIVE PROPERTIES:

Characteristic properties of system which do not depend upon the amount of system are called intensive properties.Intensive properties of system are constant with respect to the amount of system, their value does not change by change in amount of system.

EXAMPLES:- Melting point , Boiling point , Viscosity , Surface tension , vapour pressure , temperature , density etc.

STATE OF SYSTEM:-

Description about properties of system at any moment is called state of the system.

INITIAL STATE OF SYSTEM:- 

State of system before any change or experiment is called its initial state of system.

Initial temperature is represented by T1 and initial volume is represented by V1 and initial energy is represented by E1

FINAL STATE OF SYSTEM:-

State of system after any change or  experiment is called final state.Final temperature is represent by T2 and final volume is represented by V2 and final energy is represented by E2.

CHANGE IN STATE OF SYSTEM:-

Difference between the final state and initial state of a system is called change in state of system. Change in temperature is represented by DT (delta T) change in volume is reprented by DV and change in energy is represented by DE.

DT = T2 - T1, DV = V2 - V1,            DE = E2 - E1

FIRST LAW OF THERMODYNAMICS:-

It is also called law of conservation of energy.This law is give by Helm Holtz in 1847.Neither energy can be created nor it can destroyed it can be change md from one form to another.

EXPLANATION:-

According to first law of thermodynamics in a proces energy can not be created or destroyed but only energy changes between the system and surrounding or it can change from one form to anothet.Thus total energy of system and surroundinh remain constant in a process.In other words total energy of all forms of energy in universe remain constant
.

MATHEMATICAL EXPRESSION OF FIRST LAW OF THERMODYNAMICS:-

Suppose a systen with initial energy E1, it absorb some amount of heat denoted by q from the surroundings and its energy changes to E2.

Thus E2 = E1 + q

But if the system loses some energy by doing some work denoted by w then:

E2 = E1 + q-w or E2-E1 = q-w 

But as DE = E1 - E2 so DE = q-w this is equation of first law of thermodynamics.

SIGN OF THERMODYNAMICS PROCESS:-

Heat: if heat release by the system or heat absorbed by the surrounding then heat will be (-q).

If heat absorbed by the system and releaded by the surrounding then sing of heat will be (+q).

Work:If work done by system on the surroundings = -w

If work done on the system by surrounding = + w