Therme = Heat Dynamikos = work Thermodynamics = flow of heat THERMODYNAMICS Thermodynamics is a branch of science that deals with the study of inter conversion of heat with other forms of energy during physical and chemical process

HEAT  LIGHT Example? Electric Energy  Heat Example?

Thermodynamic terms System

It is a specified portion of the universe which is under thermodynamic study and which is separated from the rest of the universe with a definite boundary. Eg.?

Surrounding It is the portion of the universe excluding the system and capable of exchanging matter and energy with the system Eg.? Surrounding

Boundary The real or imaginary surface that separates the system from the surrounding is called boundary

1.Open system 2.Closed system 3.Isolated system

A system which can exchange both matter and energy with the surroundings.

A system which can exchange energy but not matter with the surroundings.

A system which cannot exchange both energy and matter with the surroundings.

It is the condition of the system expressed by giving definite values for its properties such as temperature, pressure, volume etc.

Hydrogen gas P 1 V 1 T 1 STATE -1 Hydrogen gas P 2 V 2 T 2 STATE -2

The thermodynamic properties whose values depend only on the initial and final state of the system and are independent of the manner as to how the changes is brought about. Eg. Pressure, temperature, volume, internal energy, enthalpy, entropy Analogy 

Height = h Height h of a mountain is independent of the path followed in reaching the top of the mountain. h is similar to a state function

What ? Example?

Common path functions 1.Work 2.Heat

Work = force x displacement The definition of work indicates that work depends on its path it takes, because the movement of an object is dependent upon the path taken to execute that movement. Eg. Work done by a person for climbing stairs is different from using a lift.

For instance, if a gas expands isothermally, then heat has to be supplied to the system so that the gas maintains its temperature as it expands. But if you do this adiabatically, then the system does work. Same final state (pressure and volume) but different work and heat.

The operation which brings about the change in the state of the system.

1. Isothermal process: A process which is carried out at constant temperature. ∆T = 0 2. Isobaric: A process which is carried out at constant pressure. ∆P = 0 3.Isochoric : A process which is carried out at constant volume. ∆V = 0 4. Adiabatic: A process in which there is no heat exchange occurs between system and surrounding ∆q = 0

Pressure Volume Isochoric Adiabatic Isobaric Isothermal For a given amount of ideal gas P – V relation

It is a process which is carried out infinitely slowly through a series of steps so that system and surroundings always remain almost in equilibrium state. The process is conducted in such a manner that any moment it could be reversed by a infinitesimal change.

Gas V 1 Gas V 2 Remove one particle of sand each time Reversible expansion process involves infinite number of steps. Sand It is a process which is carried out infinitely slowly through a series of steps so that system and surroundings always remain almost in equilibrium state. The process is conducted in such a manner that any moment it could be reversed by a infinitesimal change.

A process which is carried out rapidly so that the system does not get a chance to attain equilibrium.

A process during which the system undergoes a series of changes and return to its initial state. A (P 1, V 1, T 1 ) D (P 4, V 4, T 4 ) B (P 2, V 2, T 2 ) C (P 3, V 3, T 3 )

a.Intensive property Property of a system which does not depend upon the quantity of substance present in the system. Eg. Density, temperature, refractive index, viscosity, pressure,surface tension, specific heat, freezing point, boiling point, melting point, emf, pH, mole fraction, molarity etc. Intensive is independent of quantity

b. Extensive property. Property of a system which depends upon the quantity of substance present in the system. Eg. Mass, volume, energy, enthalpy, internal energy etc.

HEAT Form of energy How can we feel it? From the change in temperature Heat is the amount of energy transferred between the system and the surrounding when they are at different temperatures.

International conventions Symbol of heat = q Heat absorbed by the system = +q Example? Heat liberated by the system = - q Example?

Other method of exchange of energy between system and surrounding WORK 1.Mechanical work 2.Electrical work 3.Pressure volume work

Pressure volume work It is also called expansion work. It is significant in system which consists of gases and involve change in volume against external pressure

Gas V 1 Gas V 2

Gas V 1 Gas V 2 International conventions work done on the system = + w work done by the system = - w

Fire

It is the energy possessed by the system due to its nature, chemical composition and thermodynamic state.

Characteristics: 1.It is the sum of translational E + rotational E + vibration E + Bond E 2.It depends on mass of system 3.It depends on state of system 4.It is indicated by U 5.The absolute value of internal energy cannot be measured. 6.Change in internal energy of a system can be measured 7.∆U = U 2 –U 1

Internal energy of a system may change when: 1.Heat passes into or out of the system 2.Work is done on or by the system 3.Matter enters or leaves the system

Change in internal energy in an adiabatic system

How? 1.By rotating a small paddle inside 2.By heating with a immersion heater STATE 1 (Before the work) Temperature = T 1 Internal energy = U 1 STATE 2 (After the work) Temperature = T 2 Internal energy = U 2

Change in internal energy ∆U = U 2 –U 1 Change in temperature ∆T = T 2 – T 1 Change in internal energy in terms of work ∆U = U 2 –U 1 = W ad

Change in internal energy due to heat transfer

Change in internal energy ∆U = U 2 –U 1 Change in temperature ∆T = T 2 – T 1 Change in internal energy in terms of heat ∆U = U 2 –U 1 = q

Change in internal energy in terms of both adiabatic work and heat transfer ∆U = U 2 –U 1 = q + w Mathematical expression for 1 st law of thermodynamics

When q = 0 and w = 0 ( a state possible in an isolated system) ∆U = 0 Statement of 1 st law of thermodynamics The energy of an isolated system in constant

Energy can neither be created nor be destroyed but can be transformed from one form to another Example?

1.Work done in an isothermal reversible compression of an ideal gas w = n RT log (V f / V i ) w = n RT log (P 1 / P 2 ) n = number of moles of the gas R = universal gas constant = J/K/mol T = absolute temperature = (t o C + 273) K

PROOF

2.Work done during free expansion W= 0 3.Work done during irreversible process. W= -p∆V

Different equations for 1 st law of thermodynamics 1.A process carried out at constant volume ∆U = q v 2.Isothermal process q = -w 3.Isothermal reversible process q = 2.303nRTlog (V f /V i ) 4.Isothermal irreversible process q = P ex (V f -V i ) 5.Adiabatic process ∆U= W ad

ENTHALPY (H) ∆H = ∆U +P∆V 1. Change in enthalpy is the sum of internal energy change and the pressure volume work in a system 2.Change in enthalpy is the heat absorbed by the system at constant pressure. ∆H = q p

ENTHALPY (H) 1.It is an extensive property 2.It is a state function 3.Its unit is Joule

∆H = ∆U +∆n g RT For a gaseous reaction Where ∆ng = (Number of moles of gaseous products – number of moles of gaseous reactants) For Exothermic process ∆ H = -Ve For endothermic process ∆ H = +Ve

Sign of Enthalpy ?