Consider the following reaction at constant pressure.Use the information here to determine the value of ?S surr at 355 K.Predict whether or not this reaction will be spontaneous at this temperature.
$\quad$$\quad$$\quad$2NO(g)+ O 2 (g)? 2NO 2 (g)? r H = -114 kJ

Question

Consider the following reaction at constant pressure.Use the information here to determine the value of ?S surr at 355 K.Predict whether or not this reaction will be spontaneous at this temperature. 
$\quad$$\quad$$\quad$2NO(g)+ O 2 (g)? 2NO 2 (g)? r H = -114 kJ

Quizplus · Accepted Answer

ΔSS1U1B1surrS1U1B0 = -ΔH1U1B1rS1U1B0/T 
T = 355 K 
ΔH1U1B1rS1U1B0 = -114 kJ 
ΔSS1U1B1surrS1U1B0 = (-(-114 kJ))/(355 K) = +321 J K^-1 mol^-1

To determine whether the reaction is spontaneous, we need to compare the Gibbs free energy change (ΔG) to zero. ΔG = ΔH - TΔS. 
At constant pressure, ΔH = ΔU + PΔV. Assuming ideal gas behavior and using standard molar volumes, we can estimate ΔV as 2(-90.39 J K^-1 mol^-1) + (-205.03 J K^-1 mol^-1) - (-14.24 J K^-1 mol^-1) = -191.18 J K^-1 mol^-1. Thus: 
ΔH = -114 kJ/mol - (191.18 J K^-1 mol^-1)(355 K) = -185.3 kJ/mol 
ΔS = (2 mol)(240.03 J K^-1 mol^-1) + (44.01 J K^-1 mol^-1) - 2(2.59 J K^-1 mol^-1) = +959.9 J K^-1 mol^-1 
ΔG = -185.3 kJ/mol - (355 K)(+959.9 J K^-1 mol^-1) = -533.2 kJ/mol

Since ΔG is negative, the reaction is spontaneous. Thus, the best answer is C, ΔSS1U1B1surrS1U1B0 = +321 J K^-1 mol^-1 and the reaction is spontaneous.

Consider the Following Reaction at Constant Pressure \quad \quad \quad 2NO(g)+ O2(g)? 2NO2(g)?rH = -114 KJ A)?Ssurr = +114 KJ

Consider the Following Reaction at Constant Pressure $\quad$ $\quad$ $\quad$ 2NO(g)+ O₂(g)? 2NO₂(g)?_rH = -114 KJ
A)?S_surr = +114 KJ