Question

8) For which one of the following reactions is AHⓇxn equal to the heat of formation of the product? A) N2(g) + 3H2(g) + 2NH3 (8) B)(1/2)N2(g) + O2(g) → NO2(g) C) 6C(s) + 6H (g) → C6H6 (1) D) P (8) + 4H (g) + Br(g) - PH4Br (1) E) 12C (g) + 11H2(g) + 110 (g) → C6H22011 (8) (8) - PH4Br (1) A 9) The AE of a system that releases 12.4 J of heat and does 4.2 J of work on the surroundings is A) 16.6 B) 12.4 C) 4.2 D) -16.6 E)-8.2 10)The value of AHº for the reaction below is -790 kJ. The enthalpy change accompanying the reaction of 0.95 g of Sis kJ. 2S (s) + 302(g) → 2503 (g) A) 23 B)-23 C) -12 D) 12 E) -790 11) The value of AHº for the following reaction is - 3351 kJ: kJ. 2Al(s) + 302 (g) 2A1203 (s) 21 V 27 TU The value of AH°f for Al2O3 (s) is_ A)-3351 S4 40=100 B)-1676 C) -32.86 D) -16.43 E) +3351

Answer 1

8) Answer is b). Because in reaction b), one mole NO2 is formed from its elements hence ∆H°rxn = ∆Hf(NO2)

9) Answer is d).

∆E = q+w = -12.4-4.2 = -16.6 J

Because heat release by system is negative and also work done by the system is also negative.

10) Answer is c).

64 g S releases -790 KJ heat

0.95 g S releases -790×0.95/64 = -12 KJ

11) Answer is B).

In this Reaction 2 moles of Al2O3 is formed. Hence,

∆Hf(Al2O3) = ∆H/2 = -3351/2 = -1676 KJ