Question 3
The enthalpies of all elements in their standard states are:
 (i) unity
 (ii) zero
 (iii) < 0
 (iv) different for each element

Question 7
In a process, 701 J of heat is absorbed by a system and 394 J ofwork is done by the system. What is the change in internal energy for the process?

Question 12
Enthalpies of formation of CO(g), CO₂(g), N₂O(g) and N₂O₄(g) are –110, – 393, 81 and 9.7 kJ mol–1 respectively. Find the value of Δ_rH for the reaction:
N₂O₄(g) + 3CO(g) → N₂O(g) + 3CO₂(g)

Question 13
Given
N₂(g) + 3H₂(g) → 2NH₃(g) ; Δ_rH⁰ = –92.4 kJ mol^–1
What is the standard enthalpy of formation of NH₃ gas?

Question 14
Calculate the standard enthalpy of formation of CH₃OH(l) from the following data:
CH₃OH (l) + 3/2 O₂(g) → CO₂(g) + 2H₂O(l) ;   Δ_rH⁰  = –726 kJ mol^–1
C(g) + O₂(g) → CO₂(g) ;    Δ_cH⁰ = –393 kJ mol^–1
H₂(g) + 1/2 O₂(g) → H₂O(l) ;    Δ_fH⁰ = –286 kJ mol^–1.

Question 16
For an isolated system, ΔU = 0, what will be ΔS?

Question 17
For the reaction at 298 K,
2A + B → C
ΔH = 400 kJ mol^-1and ΔS = 0.2 kJ K^-1mol^-1
At what temperature will the reaction become spontaneous considering ΔH and ΔS to be constant over the temperature range?

Question 18
For the reaction, 2Cl_(g) → Cl_2(g),what are the signs of ΔH and ΔS ?

Question 20
The equilibrium constant for a reaction is 10. What will be the value of ΔG⁰ ?  R = 8.314 JK^–1 mol^–1, T = 300 K.

Question 21
Comment on the thermodynamic stability of NO(g), given
1/2 N₂(g) + 1/2 O₂(g) → NO(g) ; Δ_rH⁰ = 90 kJ mol^–1
NO(g) + 1/2 O₂(g) → NO₂(g) : Δ_rH⁰= –74 kJ mol^–1