Consider the reaction, 4 NO2(g) + O2(g) 2 N05(g). From the data in the table bel
ID: 542079 • Letter: C
Question
Consider the reaction, 4 NO2(g) + O2(g) 2 N05(g). From the data in the table below, the standard Gibbs Energy of this reaction at 25 °C (in kJ) is approximately (A) -63.5 kJ 1. (B) -364. kJ (C) +144. kJ (D) Insufficient data is given Compound NO2(g) O2(g) N205(g) 340. J/mol-K +33.2 kJ/mol 205. 356 +11.3 A sample of 0.5 moles of O2(g) originally at 500 kPa and 5 L is expanded reversib and isothermally to a final pressure of 100 kPa. What is S for this process? (A) +6.7 J/K 2. (B) +13.4 J/K (C) -6.7 J/K (D) +4030 J/K The constant volume molar heat capacity of CO2(9) is 28.8 J/mol-K. What is AS when 5 moles of CO2(g) is heated at constant volume from 100 °C to 400 °C? (A) +820 JIK (B) +200 JK (C) +17 J/K (D) +85 J/K A sample of 2 moles of N2(g) at 50 kPa and 20 L is compressed reversibly an adiabatically to a final pressure of 400 kPa. What is AS for this process? A) +34.6 J/K (B)0 J/K (C) -34.6 JK (D) -97.4 JIKExplanation / Answer
Relation between gibbs free energy , heat of reaction and entropy can be written as:
G = H -TS
H = 2 mol x 11.3 kJ/mol -4 mol x 33.2 kJ/mol =-11.02 kJ = -110200 J
for oxygen = 0 as it is in most stable oxidation state and it heat formation is zero
S = 356 J/mol.K x 2 mol -205 J/mol.K x 1 mol - 4 mol x 340 J/mol.K = -853 J/K
putting in equation we get:
25 oC = 298 K
G = H -TS = -110200J - 298 K x (-853 J/K) = 143994 J = +143.994 kJ ~ 144 kJ ans (C)
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