Short Answer Type
Long Answer TypeThird law of thermodynamics states: 'The entropy of all perfectly crystalline solids may be taken as zero at absolute zero.'
Molecular interpretation: Entropy is a measure of disorder. Thus, at absolute zero a perfectly crystalline solid has a perfect order of its constituent particles i.e. there is no disorder at all. Hence absolute entropy is taken as zero.
Application. It helps in the calculation of the absolute entropies of the substances at room temperature (or at any temperature T). A simplified expression for the absolute entropy of solids at temperature T is given by,
where Cp is the heat capacity of the substance at constant pressure.
Explain the effect of temperature on feasibility for:
(i) endothermic process
(ii) exothermic process in terms of Gibb’s Helmoltz equation.
Short Answer TypeLong Answer Type(a) What are Exergonic and Endergonic reactions?
(b) Given that the standard heat of formation of NH3(g) as represented by the equation
is – 46.191 kJ. The standard entropies of N2(g), H2(g) and NH3(g) are 191.62, 130.12 and 193.3 JK–1 mol–1 respectively. Calculate the standard free energy of formation (∆G0) for NH3. Is the reaction feasible?
(i) Define first and the second law of thermodynamics in the combined form.
(ii)
(a) Write an expression for the entropy change of an ideal gas for isothermal change.
(b) Write an expression for entropy change for an ideal gas for isobaric change.
(iii) Calculate the maximum work obtained when 0.75 ml of an ideal gas expands isothermally and reversibly at 27°C from a volume of 15L to 25L.
(i) What are the limitations of criterion for randomness?
(ii) Calculate the standard free energy of formation of 
The free change for the reaction.
Short Answer TypeLong Answer Type
Switch
gas?
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