All Questions page - 1341

 When liquid benzene is oxidised at constant pressure at 300 K, the change in enthalpy is -3728 kJ. What is the change in internal energy at the same temperature?

The enthalpy of formation of methane at constant pressure and 300 K is – 78.84 kJ. What will be the enthalpy of formation at constant volume?

Calculate the enthalpy change for the reaction: H₂(g) + Cl₂(g) ————-> 2HCl(g). Given that bond energies ofH-H, Cl- Cl and H-Cl bonds are 433, 244 and 431 kj mol^-1 respectively.

 The bond enthalpy of H2(g) is 436 kj mol^-1and that of N2 (g) is 941.3 kj mol^-1. Calculate the average bond enthalpy of an N-H bond in ammonia. Given: ∆H^– (NH₃) = -46 kj mol^-1

When two moles of C₂H₆(g) are burnt, 3129 kj of heat is liberated. Calculate the heat of formation of C₂H₆(g). ∆_fH for C0₂(g) and H₂0(l) are-393.5 and -286 kj mol^-1 respectively.

 1 g of graphite is burnt in a bomb calorimeter in excess of oxygen at 298 K and 1 atmospheric pressure according to the equation C(graphite) + 0₂ (g) —> C0₂ (g) During the reaction, temperature rises from 298 K to 299 K. If the heat capacity of the bomb calorimeter is 20.7 kJ/K, what is the enthalpy change for the above reaction at 298 K and 1 atm?

Define the following:
(i) First law of thermodynamics.
(ii) Standard enthalpy of formation.

Give reason for the following:
(a)Neither q nor w is a state function but q + w is a state function.
(b)A real crystal has more entropy than an ideal crystal.

(a)What is a spontaneous process? Mention the conditions for a reaction to be spontaneous at constant temperature and pressure.
(b) Discuss the effect of temperature on the spontaneity of an exothermic reaction

 Predict in which of the following, entropy increases/decreases.
(i) A liquid crystallizes into a solid
(ii) Temperature of a crystallize solid is raised from OK to 115 K
(iii) 2NaHCO₃ (s) ———-> Na₂ C0₃ (s) + C0₂ (g) + H₂O (g)
(iv) H₂(g)——>2H(g)

Why standard entropy of an elementary substance is not zero whereas standard enthalpy of formation is taken as zero?
Under what conditions will the reaction occur, if
(i) both ∆H and ∆S are positive
(ii) both ∆H and ∆S are negative

 What is bond energy? Why is it called enthalpy of atomisation?
(b) Calculate the bond energy of C-H bond, given that the heat of formation of CH₄, heat of sublimation of carbon and heat of dissociation of H₂ are – 74.8, + 719.6, 435.4 kj mol^-1 respectively.

 Thermodynamics is applicable to
(a) macroscopic system only (b) microsopic system only
(c) homogeneous system only (d) heterogeneous system only

 An isochoric process takes place at constant
(a) temperature (b) pressure
(c) volume (d) concentration

 For a cyclic process, the change in internal energy of the system is
(A) always +ve (b) equal to zero
(c) always -ve (d) none of the above

Which of the following properties is not a function of state?
(a) concentration (b) internal energy
(c) enthalpy (d) entropy

 Which of the following always has a negative value?
(a) heat of reaction (b) heat of solution
(c) heat of combustion (d) heat of formation

 The bond energy depends upon
(a) size of the atom (b) electronegativity
(c) bond length (d) all of the above