1.       Define a thermodynamically reversible process.
It is a process which carried out infinitesimally slowly so that the changes occurring in the direct process can be easily reversed without disturbing the equilibrium.
2.       Under what conditions, ∆H becomes equal to ∆E or ∆U?
∆H becomes equal to ∆U if the process is carried in a closed vessel or the number of gaseous moles of the product species is equal to the number of gaseous moles of the reactant species.
3.       Give the combined definition of first and second law of the thermodynamics.
The combined definition says that “The energy of the universe is constant but the entropy of the universe is continuously increasing and tends to become maximum.
4.       What do you mean by entropy of sublimation?
 It is the change in entropy when one mole the solid substance changes directly into vapour at a particular temperature. It is given by the relation ∆S=∆Hsub/T
               Where T= Temperature of sublimation.
5.       Name a thermodynamic quantity which is a state function but whose absolute value can be determined.
The thermodynamic quantity is entropy whose absolute value can be determined.
6.       Why does a negative value of ∆H mean an exothermic reaction and positive value an endothermic reaction?
In exothermic reactions, heat energy is evolved. This lowers the enthalpy. Consequently, the                    enthalpy of the products becomes less as compared to enthalpy of reactants. Therefore,
∆H=HP-HR=-VE
In endothermic reactions, heat energy absorbed. Heat absorbed raises the enthalpy of the products. Consequently, the enthalpy of products becomes greater than the of reactants. Hence,
∆H=HP-HR=+VE
7.       Diamond and graphite are two pure forms of carbon but heats of combustion of these two forms are different from each other. Explain.
Heats of combustion for graphite and diamond are different from each other because heat of a reaction also depends upon the physical state of the reactants and productants.
8.       A gas contained in a cylinder fitted with a movable piston is supplied heat. How do the thermodynamics functions U, H, and S are affected?
                                I.            Addition of heat will increase the internal energy. So, ∆U will be positive.
                              II.            ∆H will increase , since ∆H=∆+P∆V. Here both ∆U and ∆V are increasing.
                            III.            As gas does work against the surrounding, w will be negative.
9.       What is the difference between dissociation energy and bond energy?
The dissociation energy may be defined as the energy required dissociating (break) a given bond in a specific compound. On the other hand, bond energy is the average dissociation energy of a specific bond in a number of compounds.
10.   Why does a piece of ice feel cold to your touch?
Since the temperature of ice is lower than our finger, hence heat is transferred from our finger to the piece of ice and we feel cold.
11.   When is bond enthalpy equal to bond dissociation enthalpy?
                In case of diatomic molecules, bond enthalpy will be equal to bond dissociation energy.
12.   Explain why entropy of a perfectly crystalline substance is less than that of its imperfect crystals.
                We know that a perfectly crystalline substance is free from defects. Thus, there will no                      movement of the particles and hence its entropy will be less as compared to the imperfect                    crystalline solid.




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