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 CBSE Guess > Papers > Important Questions > Class XII > 2007 > Chemistry > Thermodynamics Thermodynamics    1 MARK QUESTION Define bond dissociation energy Why is internal energy of system is statefunction. How may the state of a thermodynamic system be defined. In what ways the internal energy of a system be changed. What is the effect of temperature on entropy Explain the state of a reaction when d G =0? State a chemical reaction when d H and d E are equal? State the second law of thermodynamics What is average bon dissociation energy for a molecule. What is the thermodynamic efficiency of Fuel Cell. 2 MARK QUESTION Define the following terms: [a] State variables of asystem [b] Internal energy of system Derive themathematical expression ofthefirst law of thermodynamics for a gaseous system undergoingexpanion at constant pressure. State Hess law How is it useul in calculating enthalpy change of a reaction? State the third law ofthermodynamics. Define an isolated system. Calculate theG for the forward reaction at450 K in the following equilibrium 2NOCl (g) --> 2NO(g) + Cl2 (g) d H = 77.2 kj/mol d S = 122 J/K?mol at 450 K 3 MARK QUESTION Define entahlpy. Show that the change in enthalpy at constant pressure , for a reaction envolving gases is given by the expression d H = d E +d n RT Calculate the free energy change and entropy change per mole when liquid water boils against 1 atmospheric pressure [ for water d H = 2.0723 kj/gm] Enthalpy and entropy change of a reaction are 40.63 Kj/mole and 108.8 J/k/mole respectively. Predict the feasibility of the reaction at 300K d H & d S for vapourisation of water at 1 atm pressure are 40.63 Kj/mole and 108.8 J/K/mole respectively. Calculate the temperature at which the free energy change for this reaction will be zero. Predict stating reason the sign of free energy change below this temperature. State the second law of thermodynamics. The enthalpy change for the formation of ammonia from nitrogen and hydrogen is -92.4 kj/mole Calculate the standard internal energy change at 298 K . 5 MARK QUESTION Mention the various thermodynamic conditions for spontaneous occurence of process.\ Illustrate with an example what is meant by standard free energy change of formation of compound State the relation between standard free energy change and equilibrium constant of a chemical reaction. The equilibrium constant at 25 C for the process Co 2+ aq + 6NH3 --> [Co(NH3)6]3+ (aq) is 2.0x10-7 . Calculate the value of d G at 25 C In which direction is the reaction spontaneous when reactants and products are under standard conditions.