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The standard enthalpy of formation of NH3 is– 46.0 kJmol–1. If the enthalpy of formation of H2 from its atoms is – 436 kJ mol–1 and that of N2 is – 712 kJ mol–1,the average bond enthalpy of N – H bond is NH3 is
-964 kJ mol-1
+352 kJ mol-1
+1056 kJ mol-1
-1102 kJ mol-1
B.
+352 kJ mol-1
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Consider the reaction:
Cl2(aq) + H2S(aq) → S (s) + 2H+ (aq) + 2Cl- (aq)
The rate equation for this reaction is
I. Cl2 + H2S → H+ +Cl- + Cl+ +HS-
II. H2S ⇌ H+ + HS- (fast equilibrium)
Cl2 + HS- → 2Cl- + H+ + S (slow)
II only
Both (I) and (II)
Neither (I) nor (II)
(I) only
D.
(I) only
For (A)
rate = K[Cl2] [H2S]
For (B)
rate = K[Cl2] [HS-] … (i)
If 10–4 dm3 of water is introduced into a 1.0 dm3 flask at 300 K, how many moles of water are in the vapour phase when equilibrium is established?(Given: Vapour pressure of H2O at 300 K is 3170 Pa; R = 8.314 J K–1 mol–1)
5.56 x 10-3 mol
1.53 x 10-2 mol
4.46 x 10-2 mol
1.27 x 10-3 mol
D.
1.27 x 10-3 mol
The volume occupied by water molecules in vapour phase is (1-10-4) dm3, that is approximately (1 x 10-3)m3
pvapV = nH2O (mol)
3170 (pa) x 1 x 10-3 (m3) - nH2O(mol) x 8.314 (JK-1 mol-1) x 300K
The energy required to break one mole of Cl— Cl bonds in Cl2 is 242 kJ mol–. The longest wavelength of light capable of breaking a single Cl — Cl bond is
(c= 3 x 108 ms–1and NA = 6.02 x 1023 mol–1)
594 nm
640 nm
700 nm
494
D.
494
Energy, E = NA
The ionization energy of He+ is 19.6 x 10–18 J atom–1. The energy of the first stationary state (n = 1) of Li2+ is
4.41 x 10-16 J atom–1
-4.41 x 10-17 J atom–1
-2.2 x 10-15 J atom–1.
8.82 x 10-17 J atom–1.
B.
-4.41 x 10-17 J atom–1
Ionisation energy of He+
= 19.6 × 10-18 J
E1 (for H) × Z2= IE
E1 × 4 = – 19.6 × 10-18 J
E1 (for Li2+) = E1 for H × 9
-4.41 x 10-17 J atom–1
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