Thermodynamics

Terms used frequently in thermodynamics System Surroundings Isolated system Closed system Open system State of a system State variables

Extensive properties An extensive property of a system is that which depends upon the amount of the substances present in the system. Examples: Mass, volume, energy Intensive properties An intensive property of a system is that which is independent of the amount of the substances present in the system. Examples: T, P, d, Conc, viscosity, refractive index, surface tension

Pocesses and Their types The operation by which a system changes from one state to another is called a process. Isothermal process Adiabatic process Isobaric process Reversible and Irreversible

Internal Energy The total of all the possible kinds of energy of a system, is called its internal energy. Δ E = E f – E in -State function - Extensive property

First Law of Thermodynamics Statement Energy can neither be created nor destroyed, although it can be transformed from one form to another. - Law of conservation of energy E=mc 2 Modified statement: The total mass and energy of an isolated system remains unchanged though it may change from one form to another. - Perpetual motion machine

Mathematical statement Δ E = q – w, where q = the amount of heat supplied to the system, w= work done by the system Enthalpy The total heat content of a system at constant pressure is equivalent to the internal energy E plus the PV energy. H = E + PV - Relation between ΔH and ΔE - Enthalpy of Vaporisation - Enthalpy of Fusion

Molar heat capacity The amount of heat required to raise the temperature of one mole of the substance (system) by 1 K. - Molar heat capacity at constant volume (Cv) - Molar heat capacity at constant pressure (Cp)

- Relation between Cp and Cv Joule-Thomson Effect The phenomenon of producing lowering of temperature when a gas is made to expand adiabatically from a region of high pressure into a region of low pressure, is known as Joule-Thomson effect or Joule-Kelvin effect.

Joule-Thomson Coefficient The number of degrees temperature change produced per atmosphere drop in pressure under constant enthalpy conditions on passing a gas through the porous plug, is called Joule-Thomson Coefficient. μ = dT/dP, μ = positive cooling μ = negative warming

Thermochemistry - Enthalpy of Reaction - Exothermic and Endothermic Reactions

Variation of heat of reaction with temperature (Kirchoff’s equations) The heat of reaction changes with change in temperature of a gas due to variation in its specific heat. Different types of heat (enthalpy) of reaction Heat of Formation Heat of Combustion Heat of Solution Heat of Neutralization Heat of Fusion Heat of Vaporization Heat of Sublimation Heat of Transition

Hess’s Law If a chemical change can be made to take place in two or more different ways whether in one step or two or more steps, the amount of total heat change is same no matter by which method the change is brought about. - Bond Energy

Second Law of Thermodynmics - Limitation of First Law - Spontaneous process - Entropy

Spontaneous Processes Spontaneous processes are those that can proceed without any outside intervention. The gas in vessel B will spontaneously effuse into vessel A, but once the gas is in both vessels, it will not spontaneously

Entropy - Concept of Entropy Entropy is thermodynamic state quantity that is measure of the randomness or disorder of the molecules of the system. Like total energy, E, and enthalpy, H, entropy is a state function. Therefore,  S = S final  S initial

Second Law of Thermodynamics Whenever a spontaneous process takes place, it is accompanied by an increase in the total energy of the universe. Reversible (ideal):

Numerical Definition of Entropy For a reversible change taking place at a fixed temperature (T), the change in entropy (ΔS) is equal to heat energy absorbed or evolved divided by the temperature (T). ΔS = q / T

Entropy change for An Ideal Gas - T and V as variables - P and T as variables

Free Energy  Concept of Free Energy  Variation of Free energy with temperature and pressure

Gibb’s Helmholtz Equations

The Third Law of Thermodynamics At the absolute zero of temperature, the entropy of every substance may become zero and it does become zero in the case of a perfectly crystalline solid.

Multiple Choice Questions Question 1 Mixing of two or more gases is a a)Spontaneous process b) Non-spontaneous process c) Reversible process d) None of these Key: (a)

Question 2 The Free Energy function (G) is defined as a)G = H + TS b) G = H – TS c) G = TS – H d) None of the above Key: (b)

Question 3 Which out of the following is not a state function a)Free energy b) work function c) Entropy d) work done Key: (d)

Question 4 When water is cooled to ice, its entropy a)Increases b) decreases c) remains the same d) becomes zero Key: (b)

Question 5 In a process Δ H = 100 kJ and Δ S = 100 JK -1 at 400 K. The value of Δ G will be a)Zero b) 100 kJ c) 50 kJ d) 60 kJ Key: (d)

Question 6 Which of the following always has a negative value? a)Heat of formation b) Heat of reaction c) Heat of combustion d) Heat of solution Key: (c)

Question 7 The heat of neutralization of a strong acid and strong base is always a)Zero b) constant c) Positive d) changing Key: (b)