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4105 Question Use the information provided to calculate the standard enthalpy of formation (kJ·mol–1) of acetylene, C2H2(g): C2H2(g) + 5/2O2(g)  2CO2(g) + H2O(l) ∆H˚ = –1299.5 kJ C(s) + O2(g)  CO2(g) ∆H˚ = –393.5 kJ H2(g) + 1/2O2(g)  H2O(l) ∆H˚ = –285.8 kJ a) –1978.8 b) –1121.4 c) 226.7 d) 453.4 Question Which statement is always true for a spontaneous reaction? a) The entropy change for the system is negative b) The enthalpy change for the system is negative c) The entropy change for the universe is positive d) The free energy change for the system is positive Question Arrange the following reactions in order of increasing ∆S value (All substances are in gaseous state): N2 + O2 = 2NO (1) 2CH4 = C2H2 + 2H2 (2) 2SO2 + O2 = 2SO3 (3) a) 1,2,3 b) 2,1,3 c) 3,1,2 d) 2,3,1 Question Which of the following reactions, in the same conditions, have the largest and the smallest value of ∆S: N2(g) + O2(g) = 2NO(g) (1) KClO4 (s) = KCl (s) + 2O2 (g) (2) C2H2 (g) + 2H2 (g) = C2H6 (g) (3) a) 1, b) 2, c) 2, d) 3, Question Arrange the following substances (1 mole of each) in order of increasing the value of entropy at 25°C and atm: (I) Ne(g), (II) SO2(g), (III) Na(s), (IV) NaCl(s), (V) H2(g) Page a) (I)