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.