Question

6. Lightning bolts have been found to enable the following atmospheric reaction: N26) + O2(g) → 2 NO(g) 4,Gº = 175.2 kJ mol-1 at 298 K a) (2 marks) The AH of this reaction is 182.6 kJ mol- and the A.Sº is 24.8J molK1. Calculate the temperature at which this reaction changes between being spontaneous to non-spontaneous. Report your answer in K. Show your work b) (3 marks) Using the reaction above, along with the knowledge that A,Gº (NO2 ) = 51.3 k) mol-1 at 298 K, calculate ArG® (inkl mol) for the following reaction at 298 K. Show your work. N02.(0) + NO(g) – N260) +06)

Answer 1

6) (a)

ΔG = Δ,Η – ΤΔ,st

When
ΔG = 0
( Transition from spontaneous to non-spontaneous)

Δ,Η = ΤΔ,s0

ΔΗ " Δ,50
, Where T is the temperature at which the reaction changes from being spontaneous to non-spontaneous

$\small {\Delta_{r}H^{0}}$ = 182.6 KJ mol-1

$\small {\Delta_{r}S^{0}}$ = 24.8 J mol-1 K-1 = 0.0248 KJ mol-1 K-1

T =
182.6 9,0248

= 7362.9 K

(b)

NO, (g) + Norg) → Nergo + Pacg) 4,4° (w0,69))51.3 ki more 7 From thermodynamic data table, AH ( NO, (q)) = 33.18 K J mol? 4 Hº (Norg) ) = 90.25 kJ molt Aptº Coace)) = 0 As t° (meco)) =0 AqHº - E4H produite] - E 44 H Creactants) -[0-(33.18 +90.25)] ; -123143 K I mola!

Aso (woo (g;) = 239.7 I morka 15" (NO cg)) = 210.5 J motsky 45" (Na ces); 19716 I mollky 45° Cocg) 3 205 I moltky

Argº - z Scproducati) - € af Sireactants) -[(191.6+205) - (239.4 +210.5)] = -53.6 J moi "k", -0.0536 KJ mollky T = 298k 16° = AH-TAS = -123.43 - 298 X-0.0536 = -107.45 kJ moles